888 THE ORGANS OF DIGESTION. 



Here and there in the alveoli are seen peculiar half-moon-shaped bodies lying 

 between the cells arid the membrana propria of the alveolus. They are termed 

 the crescents of Gianuzzi or the demilunes of Heidenhain (Fig. 484), and are 

 composed of polyhedral granular cells, which Heidenhain regards as young epi- 

 thelial cells destined to supply the place of those salivary cells which have under- 

 gone disintegration. This view, however, is not accepted by Klein. 



Serous Alveoli. In the serous alveoli the cells almost completely fill the cavity, 

 so that there is hardly any lumen perceptible. Instead of presenting the clear, 

 transparent appearance of the cells of the mucous alveoli, they present a granular 

 appearance, due to distinct granules of an albuminous nature imbedded in a closely 

 reticulated protoplasm. The ducts which originate out of the alveoli are lined at 

 their commencement by epithelium which differs little from the pavement type. 

 As the ducts enlarge, the epithelial cells change to the columnar type, and the part 

 of the cell next the basement-membrane is finely striated. The lobules of the 

 salivary glands are richly supplied with blood-vessels -which form a dense network 

 in the interalveolar spaces. Fine plexuses of nerves are also found in the inter- 

 lobular tissue. The nerve-fibrils pierce the basement-membrane of the alveoli, 

 and end in branched varicose filaments between the secreting cells. There is no 

 doubt that ganglia are to be found in some salivary glands in connection with the 

 nerve-plexuses in the interlobular tissue ; they are to be found in the submaxillary, 

 but not in the parotid. 



In the submaxillary and sublingual glands the lobes are larger and more 

 loosely united than in the parotid. 



Mucous Glands. Besides the salivary glands proper, numerous other glands 

 are found in the mouth. They appear to secrete mucus only, which serves to keep 

 the mouth moist during the intervals of the salivary secretion, and which is mixed 

 with that secretion in swallowing. Many of these glands are found at the posterior 

 part of the dorsum of the tongue, behind the circumvallate papillae, and also along 

 its margins as far forward as the apex. 1 Others lie around and in the tonsil 

 between its crypts, and a large number are present in the soft palate. These 

 glands are of tha ordinary compound racemose type. 



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 Mongolian tribes, where the front teeth are large and inclined for- 

 ward, 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 die 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, 

 covered by numerous glands 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 

 lower jaw, 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 papillse 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 froenum linguae, by which this organ is connected to the sym- 

 physis of the jaw. Occasionally it is found that this fraenum 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 



J It has been shown by Ebner that many of these glands open into the trenches around the cir- 

 cumvallate papillae, and that their secretion is more watery than that of ordinary mucous glands. 

 He supposes that they assist in the more rapid distribution of the substance to be tasted over the 

 region where the special apparatus of the sense of taste is situated. 



