326 THE ANATOMY OF VERTEBRATED ANIMALS. * 



oesophagus and the bounding of the cardiac aperture, on the 

 side of the rumen, by a raised ridge. The chewed matter thus 

 flowing over the surface of the more solid contents of the re- 

 ticulum reaches the psalterium ; and, in consequence of the fine 

 state of division of its solids, readily traverses the interspaces 

 of the lamellae of that organ, and passes into the fourth 

 stomach, there to be submitted to the action of the gastric 

 juico and to undergo the digestion of the protein compounds, 

 which have remained unaffected by the previous mastication 

 and insalivation. 



The Ruininantia are divided into three groups : a. the 

 TragulidcB, b. the Cotylophora, and c. the Gamelidce. 



a. The TraguUdoB are a remarkable family, formerly united 

 with the genus Moschus, and still commonly known under the 

 name of Musk Deer, though they are devoid of the musk-sac 

 and, in other respects, are totally diiferent from Moschus. 

 They are at present restricted to Southern Asia and Africa ; 

 and they are particularly interesting, as affording, in many 

 respects, a connecting link between the typical Ruminants and 

 the other Artiodactyla, especially the Anoplotheridue. Thus, 

 the second and fifth digits are complete in both fore- and hind- 

 feet, and the metacarpals and metatarsals of the third and 

 fourth digits unite very late, or, as in one genus, Hyoemoschus, 

 not at all. The canines are well developed in both jaws, and 

 the premolar teeth are sharp and cutting. 



The oesophagus opens at the junction of the rumen with 

 the reticulum, the communication between the two being very 

 wide (Fig. 102 B). The epithelium of the rumen is papillate, 

 and there are two oesophageal folds, as in ordinary Ruminants, 

 but the psalterium is represented only by a very short and 

 narrow tube, the lining membrane of which is devoid of folds. 



The surface of the hemispheres of the brain has fewer 

 convolutions than in any other Ruminants, though this may 

 very possibly be connected with the small size of the animal ; 

 as it is a general rule that, within the same group, the brain is 

 less convoluted in small than in large animals. 



The blood-corpuscles, small in all Ruminantia, are remark- 

 ably minute in the Tragulidce, not exceeding ±^^(,1, of an inch 

 in diameter. They have oirculai contours. 



The placenta is very nearly diffuse, the foetal villi being 

 scattered over the chorion in bands, not collected into cotyle- 

 dons. 



As further remarkable peculiarities of this group may be 

 mentioned the anchylosis of the malleolar bone with the tibia, 



