THE SALIVARY GLANDS 



1229 



Serous glands are those that secrete a thin, watery fluid, and the cells of the acini stain darkly. 

 The acini are grape-like and the cells are somewhat pyramidal in form, smaller than mucous 

 cells, and possess richly granular protoplasm. These glands are the parotid and many small 

 unnamed glands in the tongue and lips. 



Mixed glands are those in which some of the alveoli are tubular (mucous) and others grape- 

 like (serous), representing both of the above varieties in one capsule. Here belong the sub- 

 lingual and submaxillary glands. 



The arteries enter the capsule and divide into branches that enter the interlobular tissues; 

 from these vessels branches enter the lobules and form capillary plexuses around the alveoli in 

 close proximity to the basement membrane. The veins return the blood in vessels parallel to 

 the arteries. 



The nerves enter with the vessels and ultimately form plexuses in the interlobular and intra- 

 lobular tissue, the latter sending filaments that end in relation to the epithelial cells and blood- 

 vessels. In the submaxillary gland small ganglia are found in connection with the interlobular 

 nerve plexus. 



Development of the Salivary Glands. The salivary glands arise as diverticula from the 

 epithelial lining of the mouth, and their rudiments appear in the following order viz., the 

 parotid during the fourth week, the submaxillary in the sixth week, and the sublingual during 

 the ninth week (Hammar). 



;/ Crescent of Gianuszi. 



Salivary duct. 



FIG. 947. A highly magnified section of the submaxillary gland of the dog, stained with carmine. (Kolliker.) 



Surface Form. The orifice of the mouth is bounded by the lips, two thick, fleshy folds 

 covered externally by integument and internally by mucous membrane, and consisting of muscles, 

 vessels, nerves, areolar tissue, and numerous small glands. The size of the orifice of the mouth 

 varies considerably in different individuals, but seems to bear a close relation to the size and 

 prominence of the teeth. Its corners correspond pretty accurately to the outer border of the 

 canine teeth. In the Ethiopian tribes the front teeth are large and inclined forward, the mouth 

 is large; and this, combined with the thick and everted lips which appear to be associated with 

 prominent teeth, gives to the negro's face much of the peculiarity by which it is characterized. 

 The smaller teeth and the slighter prominence of the alveolar arch of the more highly civilized 

 races render the orifice of the mouth much smaller, and thus a small mouth is an indication 

 of intelligence, and is regarded as an evidence of the higher civilization of the individual. 



Upon looking into the mouth, the first thing we may note is the tongue, the upper surface of 

 which will be seen occupying the floor of the cavity. This surface is convex, and is marked 

 along the middle line by a raphe which divides it into two symmetrical portions. The anterior 

 two-thirds is rough and studded with papillae; the posterior third, smooth and tuberculated, 

 contains numerous lymphoid structures which project from the surface. Upon raising the 

 tongue the mucous membrane which invests the upper surface may be traced covering the sides 

 of the under surface, and then reflected over the floor of the mouth on to the inner surface of 

 the mandible, a part of which it covers. As it passes over the borders of the tongue it changes 

 its character, becoming thin and smooth and losing the papillae which are to be seen on the 

 upper surface. In the middle line the mucous membrane on the under surface of the tip of the 

 tongue forms a distinct fold, the frenum linguae, by which this organ is connected to the sym- 

 physis of the mandible. Occasionally it is found that this frenum is rather shorter than natural, 

 and, acting as a bridle, prevents the complete protrusion of the tongue. When this condition 

 exists and an attempt is made to protrude the organ, the tip will be seen to remain buried in the 

 floor of the mouth, and the dorsum of the tongue is rendered very convex, and more or less 

 extruded from the mouth; at the same time a deep furrow will be noticed to appear in the middle 

 line of the anterior part of the dorsum. Sometimes, a little external to the frenum, the ranine 



