382 THE ANATOMY OF VEETEBEATED ANIMALS. 



the stomacli. This opens, and then the cai'diac end of the 

 oesophagus, becoming passively dilated, receives as mnch of 

 the fodder as it will contain. The cardiac apei-ture now 

 becoming closed, the bolus, thus shut off, is propelled, by 

 the reversed peristaltic action of the muscular walls of the 

 oesophagus, into the mouth, where it undergoes the thorough 

 mastication which has been described. 



The sodden fodder is prevented from passing out of the 

 psalterial apertui-e of the reticulum, in part by the naiTOw- 

 ness of that apei-ture, and in part by the fine grating 

 formed by the edges of the psalterial laminae. But when 

 the semifluid matter, returned after mastication, once more 

 reaches the cardia. it is compelled to pass towards the psal- 

 terial end of the reticulum (even apart from the guidance 

 afforded by the lips of the oesophageal groove) on account 

 of the direction of the oesophagus and the bounding of 

 the cardiac apertiu-e, on the side of the mmen, by a raised 

 ridge. The chewed matter thiis flowing over the sui-face 

 of the more solid contents of the reticulum 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 juice and to undergo the digestion of the protein 

 compounds, which have remained unaffected by the previous 

 mastication and insalivation. 



The Ruminantia are diidded into three groups : a. the 

 Tragulidce, h. the Cotylophara, and c. the Camelidce. 



a. The Tragulidoe 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 different 

 from MoscMis. They are at present restricted to southern 

 Asia and Africa; and they are particiilarly interesting, 

 as affording, in many respects, a connecting link between 

 the typical Ruminants and the other Artiodacfyla, especially 

 the Anoplotheridce. Thus, the second and fifth digits are 

 complete in both fore and hind feet, and the metacarpals 



