408 ORGANS OP DIGESTION. 



the aliment is more masticated and softened in the mouth. 

 Its muscular tunic presents an exterior longitudinal, and an 

 inner transverse layer of muscular fibres ; the smooth mu- 

 cous coat is seldom papillated or plicated, and is lined with 

 a distinct epidermis which continues obvious over the three 

 first cavities of the stomach of ruminantia. It sometimes 

 passes much beyond the diaphragm into the cavity of the 

 abdomen, and is surrounded by the outer layer of longitudi- 

 nal cardiac fasciculi at its entrance into the stomach, where 

 its mucous coat occasionally presents longitudinal or spiral 

 folds. The cesophageal aperture of the diaphragm serves as 

 a cardiac sphincter. 



As the whole alimentary apparatus is most simple in the 

 carnivorous mammalia, from the nutritious quality and the 

 complex chemical constitution of their food, so their sto- 

 mach consists generally of a simple globular sac, without 

 internal subdivision or a ccecal portion, and the same form 

 is seen in many insectivorous quadrupeds of different orders, 

 as in monotrema, cheiroptera, insectivora, marsupialia. 

 But where the food is of a coarser or more mixed character, 

 the stomach becomes elongated transversely, and a cardiac 

 fundus or coecal portion is developed on its left extremity, 

 as we find in many of the less carnivorous tribes, and in 

 most of the quadrumana and man. In many of the roden- 

 tia, the thin membranous cardiac portion forms a considera- 

 ble coecum, and is partially separated by a constriction from 

 the more muscular pyloric half of the cavity. The great 

 development of the gastric glands around the cardiac orifice 

 of the stomach in the beaver and the wombat, is required 

 by the coarse vegetable food on which they subsist, and 

 points out an analogy between this part and the glandular 

 infundibulum at the cardiac orifice of the gizzard in birds. 

 In several phytophagous mammalia, belonging to different 

 orders, as among the pachyderma, masupialia, edentata, 

 and even quadrumana, internal folds or external coeca di- 

 vide the cavity of the stomach to a greater or less extent, 

 and from the epidermic lining extending over the cardiac 

 sacs thus formed, we observe a gradual transition to the 

 complex stomachs of the cetacea and ruminantia, where the 

 several compartments have different structures and functions. 

 Although the uses and necessities of these different forms of 



