A comparative study of the histological structure of oral glands on certain mammals

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Content A COMPAEIATIVE STUDY OF THE HISTOLOGICAL STRUCTURE OF ORAL GLANDS IN CERTAIN MAMMALS A Thesis Presented to the Faculty of the Department of Zoology University of Southern California In Partial Fulfillment of the Requirements for the Degree Master of Arts by GretChen Sihley August 1946 UMI Number: EP67163 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Disswlâtion Publishing UMI EP67163 Published by ProQuest LLC (2014). Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code uest ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ^7 This thesis, written by GEBTCHEN SIBUg A under the guidance of h^M ... Faculty Committee, and approved by a ll its members, has been presented to and accepted by the Council on Graduate Study and Research in partial fulfill ment of the requirem ents fo r the degree of MASTER OF ARTS Dean ________ Secretary 3'ANPARY 1947 Faculty Committee Chgjujnan _ ^ ^ ACKNOWLEDGEMENTS The author wishes to express her appreciation to Dr. Bruce M* Harrison for his fine criticism, help and interest which were a source of inspiration and encourage ment throughout this work. The constant helpfulness of Mr. James L. Aiken is also gratefully acknowledged. TABLE OF CONTENTS PAGE I. INTRODUCTION II. REVIEW OF LITERATURE.......... 1 Distribution of Oral Glands Among Animals . • 1 Embryonic Development ....... .. .. 2 Variation in the Structure of the Acini . . . 5 Classification and Description of Oral Glands 8 III. MATERIALS AND METHODS USED.......... 21 Materials . . . . . . . . . . . . . . . . . . 21 Methods . . . . . . . . . . . . . . . . . 21 IV. OBSERVATIONS......................................29 The Opossum . . . . . . . . . . . . . . . . . 29 The Rabbit.......................................33 The Guinea P i g ................. 36 The Hat . . . . . . . . . . . . . . . . . . . 38 The Pig . . . . . . . . . . . . . . . . . . . 40 The Cat . . . . . . . . . . . . . . . . . . . 41 The Accessory Oral Glands of the Tongue • • • 43 V. DISCUSSION........................................56 VI. SUMMARY.......................................... 61 BIBLIOGRAPHY" I. INTRODUCTION There has been a vast amount of research on certain phases of the oral glands, and the literature is quite comprehensive. However, certain differences in the paired glands of various animals have not been made clear, nor their possible significance in relation to the habits or development of the animals. The accessory oral glands have been outlined in most textbooks, but no consideration has been given to their position, frequency, characteristics, or significance. The purpose in this study has been to compare the position, size, and structure of the large paired glands in certain mammals, and to find specific information regarding the accessory oral glands in the tongue of mammals. II. REVIEW OE LITERATURE Much well established research has been done on salivary glands, which has proven a valuable foundation for further study. Terminology is likely to be confusing in dealing with this subject, since authors differ in their use of the terms oral glands and salivary glands. Usually salivary glands are thought to be only those glands which secrete digestive juices containing enzymes into the mouth, and an oral gland is one whose duct empties into the mouth; it may or may not be a salivary gland. Distribution of Oral Glands Among Animals True salivary glands are not found outside the group of mammals. In the lower forms of animal life mucous glands are more common. The lowest group in which oral glands may be found is the phylum Platyhelminthes. Molluscs have multicellular oral glands which seem to have no relation to those of the vertebrates. There are no salivary glands among the lower chordates Fish have only a few unicellular mucous glands, and amphibia have a more complicated system of multioellular oral glands. In amphibia there are a few glands on the tongue and a 2 larger intermaxillary in the lower jaw vdiioh sends its duct up between the intermaxillary bones. JMeal and Rand, 1936, state that mucous glands are found in the posterior region of the narial passages. Reptiles as a group have lingual, sublingual, and palatine; and also poison glands. The last named have a distinct place among the oral glands. Reptiles are the first animals which have the serous cells characteristic of the true salivary glands; however, it has not been proven that enzymes are secreted by these cells in the reptiles. Thus the true, enzyme-secreting salivary glands are found only among the mammalia. Embryonic Development The embryonic development of the oral glands of all mammals is similar. The glands are ectodermal in origin, for a bud of epithelium grows in from the lining of the mouth and begins to form numerous branches. These diver ti culae are solid at first and at the termination of each branch a round acinus or group of cells is formed. Later the differentiation of the epithelium becomes more complete as the ducts hollow out, beginning at the proximal end; while the acini also become better developed and capable of 3 secreting. In the meantime, the mesenchyme forms a dense capsule about each gland and invaginates at various places to divide the gland, by trabeculae, into lobules. Lowenkron, 1932, claims that the epithelial anlagen of the gland influence the formation of the embryonic connective tissue and the mantle which enfolds the gland. As the glandular cells divide they become rounded and form acini, the nuclei enlarge, and the whole cell will then stain more deeply. Fibrils of connective tissue form bundles parallel to the surface of the glands and separate the lobes from each other. When the end buds of the glands appear, blood vessels begin to grow into the connective tissue. The oral glands in the human, according to Arey, 1942, begin to develop by the end of the sixth week, that is, in the 10 mm. embryo. The parotid gland begins to emerge as a small wedge outside the upper gum, and then the tube forms and pushes back towards the ear. Acinal cells are found on the tubes at the end of five months, but complete differentiation is not found until a short while after birth. The submaxi11ary gland begins to develop at the same time as the parotid, beginning also as a small wedge between the tongue and the lower gum, and the growth extends backward 4 and vent rad underneath the lower jaw. The sublingual gland does not appear till the eighth week, when it develops as several buds growing downward between the tongue and lower jaw. The sublingual gland is composed of one large gland and about ten smaller ones lined up along the main duct. Each small duct develops separately. The growth of this gland is slower than that of the parotid or submaxillary. Arey, 1942, points out that the accessory oral glands begin to form at about three months. These glands include the molar, labial, buccal, palatine and lingual; and Hyman, 1942, also includes the infraorbital gleind which is situated along the ventral surface of the outer part of the eyebeill of the oat. Piper, 1938, has made quite an extensive study of the development of the paired glands in the 10 to 140 mm. pig. The ducts of all three glands are found in the 20 mm. pig, though the sublingual duct is nothing more than an epithe lial thickening at that stage. The submaxillary and the sublingual glands bud from the oral mucosa in the lingual sulcus and the parotid from the upper part of the buccal sulcus. In the 40 mm. pig embryo, the glands have begun to form and lumina are found in the main ducts. Variations in the Structure of the Acini There are a number of different types of cells and structures involved in the construction of oral glands. Serous cells are associated with true salivary glands; mu cous cells secrete mucous; the ducts have their own characteristic cells, and the connective tissue adds an other group of cell types. Each of these will be considered separately. 1. Serous Acini. The true glandular cells are found in groups or acini of five to eight cells. The serous acini are those which secrete digestive enzymes and are decidedly different from the mucous acini. The serous cells are small for glandular cells; they are pyramidal in shape with the apex of each cell pointing inward to form a lumen. This lumen is small since the excretion of the cells is very watery and a large lumen is not necessary. In the cell stained with Mallory* s triple connective-tissue stain or hemotoxylin and eosin, the cytoplasm shows heavy granules of zymogen which are changed to ptyalin during secretion. The cytoplasm contains sufficient basophilic material to stain darkly ; Duff and Corbett, 1945, have made an exten sive study of these cytoplasmic inclusions, many of which have no known function in the cell. The nucleus is rounded in shape and is situated towards the middle of the cell. As secretion increases, the nucleus tends to be pushed more towards the base of the cell and the cytoplasm will stain more deeply. Jordan, 1940, states that the cells of the ser ous acini rest upon a basement membrane which supports several darkly stained basket cells which are flattened and contain long, thin projections which surround the serous cells. It is thought that these cells are contractile and help to push the secretion from the serous cells, though no definite understanding of their use has been established. Another outstanding characteristic of the serous acini, according to Jordan, 1940, is the presence of canalic- uli or small canals found between the walls of the serous cells and frequently extending into these cells. They ap pear to empty into the acinal lumen; thus are assumed to be associated with the passage of digestive enzymes and juices to the salivary ducts. Serous acini are found in several of the oral glands; however, the parotid and von Ebner* s glands in the tongue are the only ones which are composed entirely of serous acini, according to Bremer, 1944. Piper, 1938, gives the pig as an exception to this. 7 2* Mucous Acini. Hartridge and Haynes, 1930, state that the mucous acini are formed of cells which are larger than the serous cells. There is less hasophilic material, and the cells stain much more lightly with the ordinary staining technique. There are commonly one or two less cells in these acini, and the lumen, while small, is always notice able and definite because of the viscid quality of the mu cous secretion. The nuclei are usually flattened, and are found near the base of the cells; and the cytoplasm appears to have a network of basophilic material throughout, but this is very faint. Bailey, 1940, states that mitochondria are also to be found within these mucous cells as well as Golgi apparatus and other cytoplasmic inclusions, the function of which is unknown. 3. Demilunes. Demilunes of Heidenhain or crescents of Gianuzzi are structures which are found on the mucous acini of both the submaxillary and sublingual glands and mucous acini of the tongue; they vary in frequency with the animal. The demilunes are caps composed of two to four serous cells found at and covering the extreme end of some of the mucous acini, or at a point which is farthest away from the intercalary duct. The function of these cells is unknown though many suggestions have been made. 8 Heidenhain, from Jordan, 1940, thought they were to replace worn-out mucous cells; however, they have never been seen dividing so that theory is discredited# Heboid and Htohr, 1879, thought that they represented an inactive stage of mucous secretion; while Solger and Krause, Jordan, 1940, have given them as true secreting cells which work inde pendently from the mucous cells# The latter is more plau sible because the cells of the demilunes contain the canaliculi characteristic of the serous acini. Classifi oat ion and Description of the Oral Glands 1. The Major Glands. The major oral glands are the parotid, submaxillary, and the sublingual which are large paired glands lying on either side of the jaw. a. Parotid. The parotid, largest of the oral glands in men, sheep, dogs, cats and rabbits, is found in front of the external ear and extends over the upper por tions of the rami of the mandible. Hill, 1937, states that in relation to the muscles in the human, it runs forward across the masseter, around the anterior border and through the buccinator, and forward to open onto the inner surface of the cheek opposite the crown of the second upper molar tooth. 9 The gland is composed entirely of serous acini and has more basket cells than any other oral gland. The con nective tissue is similar to that of the other glands, but contains much more adipose tissue, especially in older people, according to Bailey, 1940. Opening into the mouth at the second molar tooth is Stenson’s duct or the main duct of the parotid gland, the longest and greatest in diameter of all oral gland ducts. Small accessory glands are found along the main duct, and each has a duct vdiich empties into the main duct. Bremer, 1944, speaks of just one accessory parotid gland which appears as a lobe separ ated from the lobes in the main gland. Grafflin, 1942, made an interesting study of the Indian Elephant in which he found salivary structure quite similar to that of the human. In the parotid gland he discovered that fat was deposited in large amounts, and that small masses of yellow pigment were found along the striated secretory ducts in large numbers, probably for wear-and-1ear purposes. b. Submaxillary. Jordan, 1940, states that the submaxillary gland is a large gland situated anterior to the parotid and under the jaw. The main duct is Wharton’s duct which opens into the mouth on either side of the 10 frenulum of the tongue, sometimes emptying with the sub lingual duct. Both serous and mucous acini are found in the submaxillary; however, serous acini are shorter and less tubular than those of the parotid and their cells are taller, so the entire acinus is larger than that of the parotid. Cajal, 1933, maintains that the submaxillary of the cat or dog contains elongated glandular alveoli which empty into narrow straight tubules leading to the duct of Wharton. There are many demilunes found on the mucous acini; as a matter of fact Ziegler, 1937, in his study of the ox, goat, and sheep, found that the mucous acini were not pure mucous, but mixed with serous cells to form the demilunes; thus actually making the demilunes a part of the acini. The intercalary ducts of the serous acini and the demilunes are shorter while the intralobular ducts are longer. In most animals the connective tissue is more coarse than that of the parotid, and small lamellar corpuscles of simple construction are sometimes found in the interlobar tissue. Nervous tissue is more frequently found in the form of numerous sympathetic ganglia according to Jordan, 1940. c. Sublingual. The sublingual gland, smallest of the major glands, is composed mostly of mucous acini with many demilunes in all animals except in the guinea pig. 11 which has no demilunes. Jordan, 1940, says that there are no actual serous acini, hut all the serous cells are found in the demilunes. There is only one type of cell in the sublingual gland of the cat and dog, according to Weissenfluh, 1937, and the other cell types are due to morphological changes during activity. There are between five and twenty non-capsulated, accessory sublingual glands which lie along the duct of Bartholin, the main duct or ductus sublingualis major, and empty into it. Scheuerer, 1934, divides the gland into two parts in the dog. The main part is referred to as the monostomatic section composed of seromucous acini, while the polysomatic part is that which is purely mucous and empties by a number of ducts into the duct of Bartholin. Ziegler, 1937, disagrees with this and claims that there is only one kind of cell in the main part of the gleind. The sublingual gland itself lies under the tongue and empties at the side of the frenulum of the tongue. There are few intercalated ducts because of the size of the gland and the simple construction of the parts; according to Bailey, 1940, some authors claim that they are entirely lacking. In the albino rat, Thompson, 1934, has identified a mucous gland imbedded in the cephalic part of the submaxillary gland as the sublingual or retrolingual. 12 In another article, Ziegler, 1928, refers to the submaxillary and sublingual glands as the glossomandibular gland, glosso referring to the sublingual and mandibular to the submaxillary. 2. Accessory Glands. The accessory glands are num erous small glands which line the inside of the mouth and cover the tongue. They are named according to location as follows: retrolingual, von Ebner's posterior lingual, palatine, molar, buccal, labial and the anterior lingual (glands of Nuhn), and Hyman, 1942, also includes the infra orbital gland in the cat. The former is the grouping given by Hartridge and Haynes, 1930, who also say that the largest of these glands do not have more than fifty to one hundred acini. 3. Ducts. The ducts of the large oral glands follow a general pattern in most animals. The acini open into small intercalary ducts; these branch together to form the secretory ducts which in turn open into the excretory ducts which empty into the oral cavity. Hartridge and Haynes, 1930, show that the intercalary ducts are lined with cuboidal epithelium which gradually changes into columnar epithelium at the junction with the secretory ducts; the columnar epi thelium is found throughout the secretory and excretory ducts, 13 and gradually changes into the stratified squamous epithe lium of the mouth by the cells becoming superimposed upon each other. Von Ebner*s glands in the posterior region of the tongue are lined v/ith simple or stratified epithe lium and the cells are sometimes ciliated. The tubules have a delicate membrana propria, or basement membrane, surrounding the low columnar cells which lack distinct cell walls. The lumen is quite narrow because of the watery consistency of the excretion. In the parotid, the cuboidal cells have fine acidophil granules indicating a possible secretory function; Bremer, 1944, has located a few goblet cells in this region. The intercalary ducts are small, the secretory larger, and the excretory the largest. This differs in the parotid gland, which has larger secretory ducts than excretory. The mitochondria at the base of the columnar cells in the walls of the secretory ducts seem to be lined up in such a way as to give a striated appearance, while the distal zone is faintly granular; the nuclei divide the striated and granular section, according to Jordan, 1940. All the ducts are covered on the outside with a basement membrane of fibro-elastic tissue. In Stanson’s duct there are usually a few longitudinal smooth muscle 14 fibers# The ducts divide numerous times aboresoently, leaving the larger branches in the connective tissue (interlobular) and the smaller branches within the lobules (intralobular) and the intercalary ducts leading from the acini. The ducts vary in the different glands: the inter calated are longest in the parotid and absent in the sub lingual; the secretory are abundant in the parotid and rare in the sublingual; excretory ducts are found in all the glands, the ducts of Stenson and Wharton being usually larger and longer than that of Bartholin. 4. Connective Tissue. It is noted in Jordan, 1940, that the oral glands are enclosed in connective tissue which has its derivation in mesenchymal tissue. The larger glands are covered with a fibro-elastic capsule which is connected to nearby areolar tissue. From this capsule, coarse tra beculae separate and divide the glands into lobules. In turn these lobules are divided by septa from interlobular connective tissue. Interlobar excretory ducts, blood vessels, nerves, lymph vessels, and lymph glands are found in this connective tissue. Jordan, 1940, differentiates between the interlobar excretory ducts found in the con nective tissue and the interlobular secretory ducts found 15 between the lobules# The cellular structure of the con nective tissue has been described by ülara, 1934, as con sisting of reticular cells, histiocytes, lymphocytes, and undifferentiated and mesenchymal cells. Me observed in the parotid gland that there might be a potentiality towards differentiation of some of these cells into fat, blood- forming tissue, and lymph tissue. 5. Blood Vessels. The chief supply of blood to the oral glands comes from the carotid artery. Arteries follow along the path of the main ducts from the connective tissue septa into the lobules and branch as the ducts branch; thus sending smaller and smaller vessels into the glands. An abundance of small capillaries is found surrounding and entering the acini close to the basement membrane. The veins enter the interlobular tissue, and usually follow the arteries. Dabelow, 1935, in studying the development of the glands, discovered that the superficial blood vessels in- vaginate with the glands; however, as the glands grow into the deeper-lying tissue, they also acquire the blood vessels of that tissue. In the case of the sublingual and the submaxillairy, the capsule is formed early and the blood supply tends to be more centralized. In the parotid, the 16 capsule forms more slowly; consequently more of the blood supply comes from surrounding tissue and the supply is somewhat decentralized. The importance of the blood supply in glandular acti vity was demonstrated by Blinova, 1942, who reduced the supply by pressure on the arteries and produced a dimi nished secretion and an increase in the relative amount of dry substance. 6. Lymph Vessels. Little may be found in literature in regard to the lymph supply of the oral glands, for there is little lymph in this region. Most of the lymphatics are found in the areolar tissue arcfund the blood vessels and ducts, and branch in the interlobular connective tissue in which they terminate. The connection is with the lymph nodes of the cervical region. Kurdumow, 1935, has followed the path of the lymph vessels and found that in the parotid the efferent vessels divide into five main tubes. In the submaxillary, the divi sion is three. In the sublingual it is two. From all the glands the lymph passes back to the truncus jugularis. The close association of the lymphatics with the salivary glands is brought out in Bairati’s work, 1934, on the embryological development of this region. The lymph 17 glands form first in the human and contain, in their medul lary portion, the epithelial rudiments of the salivary glands* It is probable that the two types of glands are developed and differentiated at the same time* 7* Nerve Supply* Much has been written about the nerve supply of the oral glands, and some of the findings have differed* Only those more important aspects upon which most authors agree will be considerdd here. Cowdry, 1944, has found no evidence of hormonal regulation of these glands, but maintains that all the control is through the nervous system. Both the sympathetic and parasympathetic nervous systems are involved; the former sending medullated fibers directly to the gland, and the latter sending non-medul- lated fibers from local ganglia, according to Hartridge and Haynes, 1930. Bremer, 1944, Jordan, 1940, and Okamura, 1931, give the following description of the nerve supply. The para sympathetic fibers, which innervate the blood vessels, come from the superior cervical ganglion and accompany the blood vessesl into the parotid, submaxillary, and sublingual glands. The sympathetic fibers arise from the tympanic branch of the glossopharyngeal nerve, pass through the otic ganglion 18 and through an anastomosis with the auriouio-temporal branch of the mandibular nerve, accompany fibers from this branch to the parotid gland, and send some fibers to the oral glands of the tongue, according to Simonetta, 1932. The trigeminal and facial nerves send branches which pass through the sub maxillary ganglion and into the submaxillary and sublingual glands. Within the glands the nerves travel along the ducts and form microscopic ganglia and plexuses, the fibers pass through the basement membrane and surround the cells, finally resting on cellular indentations, and culminating in knob like and retiform endings. Maximow and Bloom, 1942, give several forms of stimuli for these glands. There are psychic or olfactory stimuli, and mechanical, thermal, or chemical stimuli on the nerve endings in the oral mucous membrane. Elsberg, 1943, and Reichert, 1934, have done some experimenting on the pathway of the reflex arc to find that the trigeminal or facial nerves were involved in the afferent side of the arc. The parasympathetic nerves produce a copious, watery flow of saliva ; while the sympathetic division produces a scanty, thick juice. Babkin’s study, 1932, shows that the secretory, trophic, and vasodilator impulses to the glands go through the parasympathetic nerves; and the secretory, motor, and 19 vasooonstriotor impulses come from the sympathetic system. The amount of nerve supply varies according to the animal, as Sasyhin has found, 1936. In man and the rabbit the parotid has a richer nerve supply; while in the ox, dog, and oat the submaxillary and sublingual glands have the richer supply. Secretion 1. Method of Secretion and Cellular Changes Involved. In the study of the anatomical structure of the glands, the physiological activity cannot be overlooked since there are several things to be noted in studying the structure of the cells in various stages of secretion and rest. It may be noticed that secretion is just beginning when granules are found in the cytoplasm. It is thought that these granules come from the mitochondria or perhaps from the chromatin of the nucleus or from the Golgi bodies. Ludford (Bremer, 1944) gives the following explanation, ”At the mitochondrial- cytoplasmic surface syntheses by enzymes occur. The result ing products continually diffuse into the cytoplasm, prevent ing an accumulation at the surface of the mitochondria, which would inhibit further syntheses. At the surface of the Golgi apparatus the elaborated products are concentrated 20 into droplets preliminary to their elimation." The nuclei tend to be pushed towards the base of the cells and become flattened, stain more darkly, and become concentrated. The Golgi apparatus also tends to move towards the apex of the cell. 2. Composition and Use of Saliva. According to Zoethout and Tuttle, 1940, saliva is composed primarily of water; the percentage varies between ninety-seven and ninety- nine and a half. Mucin with its high viscosity acts as a lubricant for swallowing food. Several salts are found, such as disodium phosphate, calcium bicarbonate, calcium phosphate, some potassium salts and chlorides. Salivary corpuscles and epithelial cells from the mouth are also present; enzymes : ptyalin and diastase, are present to change the starches in the diet to sugars* Several gases are found in small amounts, and carbon dioxide in larger amounts, while bacteria and molds are added in the mouth. III. MATERIALS AM) METHODS USED Materials The following animals were studied: oat (Eelis libyca domestioa), guinea pig (Gavia porcellua), opossum, (Didelphis Virginians), pig (Sus scrofa). White rabbit (Oryctolagus ounicuius), albino rat (albino of Rattus norvégiens). The rats were obtained from the supply of the University of Southern Ualifornia, the cats came from the Los Angeles City Pound, the opossums were found in the hills south of the city of Alhambra, the pig came from a slaughter house and the rabbits and guinea pigs were raised at home. In some cases it was not possible to know the exact age of the animals. One adult cat and a kitten were used. The guinea pigs were nine, six and five months old. One opossum was a young, mature female and the other was half grown. The pig was about a year old. The white rabbits were around three and four months old. Ho records were available for the rats. 22 Methods 1. Killing of Animals Cats: carbon monoxide White rats, guinea pigs, opossums: chloroform Rabbits and pig: struck on the head and beheaded 2. Preparation of Dissected Tissue for Staining. All tissues were put through the same process vdiich follows « In some cases the time varied to the extent of a half hour or so, but that probably made no appreciable difference in the results obtained. (1) Wash in a warm physiological saline solution as soon as they are dissected. (2) Place in Bouin’s Picro-Pormol fixing solution until ready for use. Preparation: Picric acid, saturated aqueous solution • 75 parts Formaldehyde . . . . . . . . . . . . . 2 5 parts Acetic acid, glacial . . . . . . . . . . 5 parts (5) 70^ isopropyl alcohol solution with a few drops of lithium carbonate, saturated solution . . . 1 hour (4) 809^ isopropyl alcohol 1 hour £3 (5) 95^ isopropyl alcohol 1 hour (6) Absolute alcohol, isopropyl • ............1-J- hours (7) Absolute alcohol, isopropyl ........ li hours (8) Absolute alcohol, isopropyl; and xylene, equal parts mixed..................................1-| hours (9) Xylene 3 hours (10) Xylene 5 hours (11) Saturated solution of* xylene and paraffin, 54°0. ....... 8 hours (12) Put tissue in a melted solution of 93% paraffin and 7% bayberry wax and keep in oven at 54^0. for infil trating for six hours, changing tissue to a new solution at the end of each two-hour period. (13) Imbed in same type of solution, allow to cool and harden, and mount on wooden block for sectioning on the microtome. (14) Cut tissues from 6 to 25 micra, according to future study needs. (15) Float tissues onto.slides prepared for adherence with Mayer’s Albumin Fixative prepared as follows: Beat white of egg Allow to stand and skim off suspended matter Filter through a suction filter 24 Add remainder to an equal volume of glycerine Add salicylate of soda to the extent of 1 gram for each 50 cc* of fixative, or a crystal of thymol for the prevention of putrefaction 3. Staining. Four different staining techniques were used and portions of the tissue from all the animals were stained by all of the first three methods in order to show different structures and give a clearer understanding of their characteristics. The fourth method of staining was used only for one rabbit’s tongue which was to be comple tely sectioned to find the location of all the oral glands in it. (1) Heidenhain*s Iron Hematoxylin Preparation of solutions: Solution 1 Ferric alum . . . . . . . . . . . . 0«5 grams Distilled water ............ 100 cc. Solution 2 Hematoxylin . . . . . . . . . . 0.5 grams Distilled water . . . . . . . . . . 100 cc. 98% alcohol 10 cc. Dissolve hematoxylin in alcohol and add water. Allow the mixture to ripen for about two months in the light. 25 Staining technique: Xylene ............................. 1-5 minutes Xylene 1-5 minutes Absolute alcohol . . . . . . . . . . 1-5 minutes Absolute alcohol . 1-5 minutes alcohol 1-5 minutes 70% alcohol 1-5 minutes Distilled water 5 minutes 2.5 aqueous solution of ferric alum . . . 20 minutes Tap w a t e r ............................. 20 minutes Hematoxylin 15 minutes Distilled water . .................... rinse 2.5 aqueous solution of ferric alum . . . 10 minutes Tap water 5 minutes Eosin, 95% alcohol.....................20 minutes 70% alcohol 1-5 minutes 95% alcohol.......... ....................1-5 minutes Absolute alcohol . . ......... •.•••• 1-5 minutes Absolute alcohol . . . . . . . . . . . . 1-5 minutes Xylene 1-5 minutes Xylene . . . . . . . . . . . . ......... . 1-5 minutes Mount cover slide with Canada beisam or gum damar and allow to harden before using. 26 (2) Delafield’s Hematoxylin Preparation of solutions: Solution 1 Saturated solution of ammonium alum # 100 co* Hematoxylin crystals . . . . . . . . 1 gram Absolute alcohol . . . . . . . . . . 10 co. Dissolve the hematoxylin crystals in the absolute alcohol. Add this solution to the ammonium alum solution drop by drop with constant stirring. Allow to ripen for several weeks in the light. Filter and add 25 co. of methyl alcohol and 25 cc. of glycerin. Solution 2 Eosin . . . . . . . . . . . . . . . . 0.5 grams Alcohol, 95% . . . . . . . . . . . . 100 cc. Staining technique Remove paraffin and run down to distilled water as in first process Hematoxylin . . . . . . . . . . . . . . . . 2 0 minutes Tap water . . . . . . . . . . . . . . . . . . rinse 70% alcohol with a drop or two of hydrochloric acid . . dip once or twice to destain to a reddish color Tap water ..... rinse well to remove acid 27 Eosin .............................25 minutes Dehydrate as before Clear in xylene as before Mount in balsam as before (3) Mallory*s Triple Connective Tissue Stain Preparation of solutions: Solution 1 Acid Fuchsin .... .. .. .. 0.2 gram Distilled w a t e r 100 cc. Solution 2 Analine Blue, Grubler* s water soluble . 0.2 gram Orange G, Grubler* s . . 2.0 grams Phosphomolybdic acid, 1% aqueous sol. . 100 cc. Staining technique Remove paraffin and run down to distilled water as before Stain in solution 1 ................ 5 minutes Stain in solution 2 . ...................10 minutes Destain in water or 70% alcohol (alcohol usually works better with most tissue because the water destains too much of solution 2) Absolute alcohol . . . . . . . . . . . . . 1-3 minutes Absolute alcohol . . . . . . . . . . . 1-3 minutes 38 Xylene ............... 1-3 minutes Xylene # . ......................... 1-3 minutes Mount in balsam (4) An entire rabbit*s tongue was sectioned and mounted on larger slides* Mallory’s triple connective tissue stain was used, but a slightly different process was employed because of the thickness of the tissue and the necessity for saving as many of the sections as possible. Xylene ................... . 1-3 minutes Xylene ................... 1 minute Celloidin, in ethyl alcohol . . # 4-5 minutes Hold slide out of solution for a few seconds to set celloidin Distilled water 5 minutes Solution 1 5 minutes Solution 2 . 10 minutes Destain in 70% alcohol ...... ÿ hour or longer because of celloidin which holds the stain Dehydrate Clear in xylene euid mount in balsam IV. OBSERVATIONS Information gained from studying the slides made from the salivary glands of the various animals will he presented in relation to each animal, and a comparison made in the discussion later. The larger paired salivary glands, the submaxillary and the parotid, will be considered first; the accessory glands of the tongue will be presented at the close. The Opossum The parotid gland of the opossum is found directly below the ear at the ascending ramus of the mandible, while the submaxillary is slightly median and somewhat cephalad to it, as shown in Figure 1. Neither of the glands is rela tively as large as those found in the other animals studied, and their general construction is more compact and rounded as compared to the flattened, diffuse glands of the rabbit and Guinea pig. Viev/ed under the microscope, the salivary glands of the opossum reveal unique differences from the other animals. The lobes of the glands are triangular in shape, though the lobules tend to be rounded. In both the submaxillary and parotid, there is more basophilic material in the cytoplasm 30 PAIRED ORAL QLAADS in THE opossum LATERAL vieUJ ÜT sKin Figure 1# 31 and the nuclei are larger; see figure 2* The acini of the submaxillary average 0*033 mm* in diameter and reveal when sectioned about four or five cells each; which are characterized by large, rounded, centrally located nuclei* The acinal cells are all nucous, but there are numerous demilunes at the rate of about one to each three acini. The demilunes are composed of two or three very thin and darkly stained cells, which are serous but contain flattened nuclei. There are no fat cells in any part of the gland or in the surrounding connective tissue* The ducts are numerous, between thirty and thirty-five to the field of the medium power objective of the microscope used, which gives 440 magnification; and follow the usual pattern of cuboidal cells which line the intercalary ducts and columnar cells in the secretory* The acini of the parotid gland are all serous and average 0*032 mm. in diameter when sectioned, almost as large as those of the submaxillary; however, there are usually six cells observed in section of each acinus, whereas the submaxillary has but five, making the parotid cells much smaller. Here too, we find unusually large nuclei and poorly defined cell membranes. There are about forty to forty-five ducts in the field of the X 44 objective and X 10 Figure 2. Cross section through the submaxillary gland of the opossum showing the mucous acini, ducts, and demilunes. IX 792) S - Mucous cell L - Lumen in center of acinus A - Acinus N - JNucleus in mucous cell DE - Demilune of Heidenhain D - Duct 32 Figure 2 5 5 eyepiece, and most of these are intercalary as in the submaxillary. The Rabbit The parotid gland of the rabbit is a large, diffuse gland v/hich is ventrad of the ear and immediately caudad of the ascending ramus of the mandible, as shown in figure 5. The duct runs cephalad over the masseter muscle and into the mouth near the diastema of the mandible. It is composed of large, rounded lobes broken up into smaller lobules characteristic of most salivary glands. The acini, averaging 0.045 mm. in cross section, are the largest of any glands studied. They are composed of serous cells, usually seven in number, formed around a large lumen, seen in figure 4. There are no demilunes, no fat, and few ducts. The ducts are ill-defined, mostly inter calary, and found at frequencies of about two or three to the X 44 objective field and X 10 eyepiece. The submaxillary gland of the rabbit is ventrad and cephalad to the parotid with a duct leaving the dorsal side of the gland, passing between the digastric and masseter muscles, and entering the mouth near the medial line at the base of the tongue. The glands of the rabbit are difficult LflTERRL VIELL) 54 PAIRED ORAL QLAADS in THE flLBino RABBIT PAROTID Figure 3. Figure 4* Cross section through the parotid gland of a rabbit showing the serous acini of which it is composed» (X 792) 0 - Connective tissue surrounding lobules A - Acinus of serous cells S - Serous cell L - Lumen in the center of the acinus N - Nucleus in the serous cell 35 Figure 4 36 to dissect out, for they are diffuse and run together in an interlacing manner. The sectioned acini measure about 0.033 mm. in largest diameter and are of two types; one is the serous and the other is the mucous, the latter numbering about four to each of the serous. The mucous acini contain four cells each around a well-defined lumen, while five cells are found in most of the serous acini. Demilunes of Heidenhain are found at the rate of about one to eight or ten of the acini; they are composed of two or three ill-defined, thick cells with centrally located nuclei. The connective tissue of the gland is characterized by a limited number of fat cells. Ducts are found at twenty-five to thirty in a X44 objective field and X 10 eyepiece, and contain stratified cuboidal epithelium between the cuboidal and columnar types of the intercalary and secretory ducts respectively. The Guinea Fig In this animal, the parotid is the smaller of the two large glands. It is found laterad and dorsad to the masseter muscle and cephalad to the ascending ramus of the lower jaw, as shown in figure 5. The acini are composed of five and six serous cells, poorly defined, but compact and LA TE P .A L VtEUÜ 37 PAIRED ORAL GLADD5 in THE GUIflER PIG EAR CUT SKin PAROTID SUftm AXILLRRY mAADIDLE Figure 5. 38 averaging 0#026 nnn. in diameter. The interlobular connective tissue contains about five or six fat cells to the lobe. Seven to nine ducts lined with ill-defined cuboidal epithe lium are found in the JL 44 objective field and X 10 eyepiece. The submaxillary gland is a much larger diffuse gland lying ventrad and caudad of the parotid. Mucous acini are found at the rate of twelve to fifteen for each serous type and both measure 0*025 mm. in an average section. The mucous acini contain six cells, and the serous five, vdiile the numerous demilunes are made up of three to four cells each. Fat is more generously distributed in the connective tissue in this gland than any other studied, and is found in the connective tissue around the acini. The X 44 objective field reveals four or five ducts which show stratified cuboidal epithelium in the transition between simple cuboideüL and simple columnar. The Rat The parotid gland of the white rat is ventrad and caudad of the ear, and is the smaller of the two large glands; this is shown in figure 6. The acini contain only serous cells, average 0.029 mm. in diameter, and contain £in average of six cells in cross section. Fat is confined to the connective tissue between the lobules at the frequency 39 PAIRED ORAL GLAAD5 in THE RLbinO RAT VEOTR.RL v»eu3 - LO W E R . JBUJ PAROTID ^----- P0fc>i“ Tior> 1 O F E A R . 5UBmBX»LL««.Y Figure 6. 40 of one fat cell to twenty serous. Ducts lined with cuboidal epithelium and containing a very small lumen are found at the rate of twelve to sixteen in the X 44 objective field and X 10 eyepiece. The larger submaxillary gland, found mediad and caudad to the parotid, is made up of large acini, averaging 0.037 mm. in diameter in cross section. There are three serous acini to every mucous acinus, with a demilune for an average of ten to twelve mucous acini. The mucous acini contain six to seven cells, the serous contain five, while three or four well-defined cells make up the demilunes. The intercalary ducts number three and four to each X 44 objective field and X 10 eyepiece. Very few secretory ducts occur. The Pig The submaxillary gland of the pig, found ventrad and cephalad of the ear, is composed of one serous acinus to each eight mucous acini, both types measuring an average of 0.032 mm. in diameter in section. Approximately five cells make up the serous acini, seven cells for the mucous, and four or five for the numerous demilunes. Only an ocassional fat cell is found in the connective tissue. Ducts are more 41 numerous in this gland than any other, for they are found at the rate of ninety to one hundred and ten to the X 44 objective field and X 10 eyepiece# These ducts are lined with well-defined cuboidal and columnar epithelium. The Cat The parotid gland is the largest of the paired sall- varies in the cat, and is found directly ventrad to the ear, covering the ascending ramus of the mandible, as seen in Figure 7. The serous acini average 0.030 mm# in diameter in section and contain an average of five cells. There is a tendency towards stratification of the cuboidal cells in the transition to columnar in the ducts, which number fifty to sixty to the X 44 objective field and the X 10 eyepiece# Almost on the median line and ventrad to the parotid gland is found the submaxillary . The acini average 0.037 mm. in diameter, contain six cells to the mucous acinus and five cells to the serous acinus. There are ten mucous acini to each serous acinus and numerous demilunes, each composed of four or five cells. Forty to fifty ducts are found in each field of the X 44 objective and X 10 eyepiece. They are characterized by well-defined cells and large lumen# 48 VEHTRAL VlEiJÜ PAIRED ORAL GLAADS in THE CAT - LOWER. JRUJ -C U T SKIO — m O LA R GLROO 6V6mAXlLLARY P A R O T ID iTigure 7. 43 The Aooesaory Oral Glands of the Tongue Little information has been published in regard to the accessory oral glands of the tongue# In order to deter mine what types of glands were in the tongue, where they were, and how numerous; the entire tongue of a young rabbit was sectioned. The tongue was sectioned in two ways to better ascertain the position of the glands. It was first divided along the median line, the right half sectioned transversely and the left half sectioned saggitally. Three types of glands were found: serous glands, known as von Ebner’s glands, mucous glands with acini, and tubular mucous glands without acini. The glands of JMuhn, usually found in the anterior portion of the tongue, according to literature, were not found in the rabbit. Going back to the embryological development, we find that the muscle tissue has pushed up from the mesenchyme of the arches in the floor of the mouth to take its place in the tongue, while the ectodermal epithelium is pushed upward from the mandibular arches to form the main part of the tongue; and the epithelium of the posterior region is ento- dermal in origin, being pushed forward from the second, third, and fourth branchial arches. The two forms of epi thelium meet along the line of the terminal sulcus, or the 44 V-shaped groove in the posterior caudal region. At the point of the V, at the median line, the foramen caecum may be identified in section by a triangular core of connective tissue, shown in figure 8, which is conical in shape with the base of the cone at the surface epithelium of the tongue and the apex connecting with the median septum. The invagination of the surface epithelium forms the anlagen of the glands of the embryo; later lumina form and the ducts branch into acini. The von Ebner’s glands arise from the gradual deepening of the trenches about the circum- vallate papillae, according to Arey, 1942. After the trenches form, the ducts of the glands continue to grow inward, acini form, and the lumina of the ducts open. Thus, the ducts of von Ebner’s glands all open into the trenches of the cir- cumvallftte papillae as is shown in figure 9. Both the tunica propria and the stratified squamous epithelium in- vaginate to form the trenches, but cuboidal epithelium is found in the ducts which push through both the tunica propria and the connective tissue, and run between the muscle fibers to reach the small lobes of the glands. The acini of von Ebner*s glands are strictly serous in character, being formed entirely of serous cells which stain in the usual manner with all three techniques used. Figure 8. Cross section through the posterior region of a rabbit's tongue showing the connective tissue core which composes the foramen caecum. (X 110) 0 - Core of connective tissue in the shape of a cone with the apex ventral in the muscle tissue and the base dorsal, resting on the basement membrane of the epithelium E - Epithelium on surface of tongue M - Muscle tissue F - Fat cells 45 m Figure 8 Figure 9# Cross section of the posterior region of a rabbit's tongue showing the circumvallate papillae, their deep trenches lined with taste buds, and the ducts of the serous glands emptying into the trenches. (X 110) P - Papilla TB - Taste buds T - Trench about circumvallate papilla D - Duct of serous cells emptying into trench 46 Figure 9 47 except for the fact that the cytoplasm seems to contain more than the usual amount of basophilic material. This was found when certain sections were stained at the same time as the parotid tissue from the rabbit and the rat, and the serous cells of the tongue took a deeper stain. The acini average 0.02 mm. in diameter and each is formed of four or five serous cells, as seen in section. Obviously the muscle fibers have been formed and placed before the glands have formed, because the glands are shaped by the position of the bundles of muscle fibers. This gives the lobes either a triangular or a sharply elliptical shape. Often the strands of the muscle cut directly through the lobes of the glands; see figure 10. Because the lobes of the glands are small, there are few ducts, usually only one or two, to each lobe. The length of the entire tongue which was sectioned, was 46 mm. ; the serous glands, between thirty and forty in number, are found at 51 mm. and running to 39 mm. from the tip. They are centrally located dorsad and ventrad and found in two groups, each of which is placed in the outer third of the tongue for the most part, leaving the middle third over the medial line practically free of von Ebner*s glands. This is illustrated in figures 11 and 12, which Figure 10. Cross section through the posterior region of a rabbit's tongue, showing the serous and tubular mucous glands in their relative position to each other and to the muscle and fat tissue of that region. IX 188) T - Tubular mucous gland S - Serous glands, Ivon Ebner's) in triangular lobes F - Fat cells M - Muscle tissue L - Lumen in the tubular mucous gland Figure 11. I l ci o gg 5 0 —I o Œ c § i i ! eg uJ c Lü (X X . Q j » - E (X o c 3 O X *n w 3 . O 'J M . T O tO o CC X H- X VD oC 49 t/)_ c S Œ V 3 0 |î £3 il «o - i g Ü il £ 48 Figure 10 Figure IS, Ü Od o O-i £S cQO (Ce O CE d o il -j Œ S o o o c °o XlxJ UJ üJ od X H- CE x g 2 o H" fe e U J X VJ iO # I 5 tu E a 5 £ t I S 50 I i 63 «o i i l 10 o 3 s ou in<n 1 1 e 51 Show the glands from the medial and dorsal surfaces. Two different types of mucous gleoids are found in the tongue. At the hase of the tongue, beginning at ZS mm. from the tip and extending to 37 mm., there are two glands formed of about a dozen lobes each. They run along the ventrad side, at the same time pushing dorsad to the same plane as the first serous glands which they meet, and then extending from the base around the lateral side of the tongue. Figures 11 and 12 also show the position of these glands. The glands are formed of mucous cells arranged in the form of acini at the terminals of the ducts. The acini measure 0.026 mm. in diameter and are capped with an occasional demilune composed of two or three serous cells. The ducts are found at the frequency of three or four to the lobe and are lined with cuboidal epithelium. With Mallory* s triple-connective tissue stain, the result in the mucous acinal cells is a reddish purple color, revealing more basophilic material than in the other mucous glands of the tongue, and larger, more centrally located nuclei, as illustrated in figure 13. The second type of mucous gland is much more prevalent in the tongue, as is shown in figures 11 and 12. The general structure seems to be that of a compound tubular gland. Figure 13. Gross section through the acinal mucous gland at the base of the rabbit’s tongue, showing the structure of the acini. (X 376) A - Mucous acinus L - Lumen in the center of the acinus G - Gonnective tissue surrounding the lobules 52 Figure 13 53 The cells are mucous, but are flattened to almost give the appearance of columnar cells as they line the tubes; see figure 10. The groups of cells as they are out in cross section measure 0.054 mm. in diameter, and the individual cells are a third again larger than the cells of the mucous acinal group. Apparently the chemical composition also differs, because with the Mallory’s stain, only a light blue color results. The nuclei stain with the same inten sity as those of the mucous acinal cells, but are somewhat smaller and more frequently located at the base of the cells. Small groups of serous cells, three or four in number in cross section, form various-shaped demilunes over the ends of the tubes. However, these too do not stain the same as the serous cells of the von Ebner's glands. The cells are larger, have less distinct cell walls and stain more lightly with more of a reddish color than the blue of the von Ebner* s glands. Ducts are not found in the lobules of the glands, for the tubes probably take over their work; however, ducts form just inside the lobules and pass through the muscle, connective tissue, and epithelium of the tongue to empty between the papillae at the surface of the epithelium, as is shown in figure 14. The ducts are lined with cuboidal epithelium which gradually unites with the stratified Figure 14# Cross section through the posterior region of a rabbit's tongue showing the duct passing from the tubular mucous cells and through the epithelium to empty on the surface of the tongue# (X 188) E - Epithelium F - Fat cells D - Duct 54 Figure 14 55 squamous epithelium of the surface of the tongue# These tubular glands begin at 36 mm. from the tip of the tongue and continue to the end, becoming more and more numerous until there is nothing but epithelium and glandular tissue at the root of the tongue for the last 6 mm# This is probably because the muscular tissue originally came from the floor of the mouth and the root of the tongue is in the pharynx which contributed mucous tissue rather than muscle tissue to the construction of the tongue in the embryological development # 56 V. DISCUSSION There seems to be no particular connection between the characteristics of the oral glands of the various animals and their food or phylogenetic relationship. Since the oral glands of invertebrates and certain lower forms of verte brates are merely mucous glands, research might be expected to reveal an increasing development of the glands in higher forms with a greater percentage of serous cells in the more complicated body systems; but this has not been borne out in this study. There seems to be no relationship between the type of food the animal eats, the method of taking in the food and passing it to the throat, or the phylogenetic position of the animal, and the structure of its glands. The characteristics of the oral glands differ in each animal to such an extent that few general statements will apply to all or the great majority. Many of these character istics are not discussed in literature# The embryonic origin of the oral glands is from the ectoderm in most oases; however, those in the posterior region of the tongue, caudad to the terminal sulcus, are of entodermal origin. Neal and Rand, 1936, state that the glands of the tongue "are formed by the local prolification of the 57 stratum germinativum of the mucous lining of the mouth," as an exception to the ectodermal origin; but since the stratum germinativum is ectodermal epithelium, there seems to be no exception in their general statement. It is generally agreed that there are three paired oral glands considerably larger than any others found in the oral cavity. The position, shape, and size of the glands differs markedly in various animals, though most writers make no reference to this. Bremer, 1944, states that the parotid is the largest of the glands, and while this is true in some cases, in others it is not. In research for this paper it was found that the guinea pig and albino rat both have parotid glands "which are smaller than the sub- maxillary. In most animals the cells of this gland are all serous; that is, those -which stain more darkly with such stains as Mallory's triple-connective tissue stain, group themselves about a very small lumen, and have large, centrally located nuclei, reveal numerous intercalary ducts, and release enzymes in their excretion. The submaxillary gland is usually analler in higher mammals than the parotid, and is located cephalad and median to it. Two types of acini are found: mucous and serous, with demilunes of serous cells often occurring at the extra- 58 mities of the mucous acini. The mucous acini have larger cells and lumina, lighter staining qualities, and nuclei which are often found flattened at the bases of the cells because of the mucous in the cells. These cells secrete a copious amount of viscid fluid without enzymes. The sublingual is the smallest of the paired glands and is found cephalad to the submaxillary gland. Often it is just a series of small glands emptying into a common duct. The acini are mixed as in the case of the submaxillary; in the sublingual there are more mucous and fewer serous, but more demilunes. In many animals this gland is absent. In some animals, such as the opossum and rat, the paired glands are small and compact, resembling lymph glands in gross appearance; while in other animals, such as the rabbit, the oral glands are flattened, diffuse, and dif ficult to dissect from their surrounding tissue. Hartridge and Haynes, 1930 and Bailey, 1940, state that the nuclei of the mucous cells are flattened and tend to rest at the bases of the cells during secretion. However, it was observed that even in time of secretion, large per centages of the nuclei maintained their large, well-rounded condition. It is also interesting to note in the opossum the flattened condition of the nuclei in the serous cells 59 composing the demilunes, since such nuclei are usually round. No mention is made in the literature of the strati fication sometimes found in the ducts of the oral glands. The usual plan presented is cuboidal epithelium lining the intercalary ducts, and columnar lining the excretory ducts, gradually changing to the squamous mucous epithelium of the mouth. However, it is noted in the parotid of the cat euid the submaxillary of the rabbit and guinea pig, that a strati fied cuboidal epithelium exists in the transition between the cuboidal and columnar epithelium. Little is written about the accessory glands of the mouth. They are named according to where they are found: buccal, retrolingual, von Ebner's posterior lingual, palatine, molar, labial, anterior lingual, and infraorbital. Most authors agree that they are all mucous with the exception of von Ebner's glands of the tongue which are serous. Hartridge and Haynes, 1950, state that none of these glands have more than 50 to 100 acini, but do not mention in which animal; however, it is found that the mucous acinal type at the base of the tongue contain closer to a thousand acini. These glands are not mentioned in any of the available literature, and the mucous glands which are mentioned and 60 grouped with the oral glands are those at the base of the tongue which have little resemblance to oral glands, since they are tubular rather than acinal in structure. This shows an interesting association to the development of the tongue; since the anlage of the tongue develops from the mesenchyme of the arches in the floor of the mouth, the oral glands in this section more closely resemble those of the rest of the oral cavity, both serous and mucous. The tubular mucous glands are found in the extreme posterior portion of the tongue where they resemble the mucous glands of the throat, probably because the root of the tongue originated from the mucous membrane of the throat, pushed forward dur ing embryonic development from the branchial arches. VI. SUI/MARY A comparative study of the parotid and submaxillary glands of six small mammals reveals the following outstanding differences: the parotid gland in the opossum is quite different from that of the rabbit, guinea pig, rat, pig and cat. The gland in the opossum is smaller, more compact, formed of triangular lobes, acinal cells containing more basophilic material than in other animals, and larger nuclei. The ducts are far more numerous except in the case of the cat which has more ducts than the opossum. The ducts in the parotid of the cat and the submaxillary in the rabbit*and the guinea pig both show a stratified cuboidal condition between the cuboidal and columnar linings of the ducts. In the rabbit, opossum, and cat the parotid is larger than the submaxillary, but in the other three animals the parotid is smaller than the submaxillary. Usually the glands are rather compact, but the rabbit has a singularly diffuse organization and also differs in the size of the acini, which are twenty-five percent larger than those of any of the animals studied. Usually the submaxillary is cephalad of the parotid; however, in the rat it is caudad and in the cat it is on the same level, but mediad. There is a large variation in the 62 type of acini found in these animals, most of them have both serous and mucous acini, except the opossum which has only mucous. Numerous serous are found in the rabbit and rat, and fewer in the other animals. Ducts are much more numerous in the submaxillary than in the parotid, except for the guinea pig and rat which have fewer. The pig is outstanding in the number of ducts, having at least twice as many as any other animal. Demilunes in the submaxillary are unique in the opossum, where they are composed of many narrow, compact cells which have flattened nuclei and an abundance of baso philic material. The glands of the tongue were not studied comparatively between animals, but as a unit in the rabbit. Three types of glands were found in the caudal region: acinal mucous, tubular mucous, and serous. The acinal mucous are compact, and found at the base of the tongue running along the floor of the mouth. These compare in likeness to the mucous glands of the oral cavity. The tubular mucous glands occur at the back of the tongue, and resemble the glands of the throat to which they are more closely related. The serous glands are also found in the posterior portion of the tongue, along the line of the terminal sulcus, except at the foramen caecum which remains as a core of connective tissue below the 63 epithelium. These are characteristically oral glands, staining more deeply than the paired glands and containing smaller cells and lobes. BIBLIOGRAPHY Arey, Leslie Brainerd, 1942, Developmental Anatomy. A Text book and Laboratory Manual of Embryology. Eourth Edition, Philadelphia and London, W. B. Saunders Co. 612 pp. Babkin, B. P., 1932, "The Innervation of the Salivary Glands," Trans. Royal Society of Canada, Sect. 5, 25:205-11. Bairati, Angelo, 1931, "Concrescenza fra gangli linfatici e canalicoli salivari nel filo umano," Boll. Soc. Ital. Biol. Sperim., 6(1): 27-29, Bensley, R. P., 1908, "Observations of the Salivary Glands of Mammals," Anat. Rec. (2) 105. 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Creator Sibley, Gretchen (author)

Core Title A comparative study of the histological structure of oral glands on certain mammals

Contributor Digitized by ProQuest (provenance)

Degree Master of Arts

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Biological Sciences,OAI-PMH Harvest

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Language English

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c39-274485

Unique identifier UC11315787

Identifier EP67163.pdf (filename),usctheses-c39-274485 (legacy record id)

Legacy Identifier EP67163.pdf

Dmrecord 274485

Document Type Thesis

Format application/pdf (imt)

Rights Sibley, Gretchen

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

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University of Southern California Dissertations and Theses