236 COMPARATIVE ANATOMY. 



Herbivorous Mammals, as a rule, possess a larger and more 

 complicated stomach than do Carnivorous Mammals (comp. Fig. 

 192, A to G), 1 and it may become divided into two or more chambers. 

 Thus in Ruminants (Fig. 192, E) there are four chambers, which 

 are called respectively, rumen (paunch), reticulum, psal- 

 terium, 2 and abomasum. The two first simply serve as storage 

 cavities, the food returning from them into the mouth, once more 

 to undergo mastication. It then passes into the psalterium, and 

 finally into the abomasum, the latter alone being provided with 

 rennet (gastric) glands, and serving as the true digestive stomach. 

 (The dotted arrow in Fig. 192, E, shows the course which the food 

 takes.) 



The small intestine is usually long, and varies more as to length 

 and diameter in domesticated than in wild forms. Commonly, as 

 in the human subject, the relative length of the small intestine 

 is less in the foetus than in the adult. 



The large intestine, which is made up of a varying number of 

 coils, usually reaches a great length in Mammals, and its diameter 

 is much greater than that of the small intestine : these two por- 

 tions are thus sharply marked off from one another, and the 

 distinction between them is rendered still more marked by the 

 sacculations of the anterior part of the large intestine. Only the 

 posterior portion of the latter, or rectum, which passes into 

 the pelvic cavity, corresponds to the large intestine of lower 

 Vertebrates ; the remaining and far larger part, must be looked 

 upon as a neomorph, and is called the colon. In this, further 

 subdivisions may often be distinguished, e.g. in Man. 



The caecum, which is almost always present, undergoes the 

 most various modifications both as to form and size, according 

 to the kind of nutriment. Thus in Carnivora, Odontoceti, 

 Insectivora, and Cheiroptera, it is very small or even entirely 

 wanting, while in Herbivora, it may exceed the whole body in 

 length. An inverse development in size is usually noticeable 

 between it and the rest of the large intestine. In many cases 

 (many Monkeys, Rodents, and Man) an arrest of a portion of 

 the caecum takes place in the course of individual development 

 (Fig. 172, Pv\ giving rise to a processus vermiformis. In 

 Lepus, the enormous caecum is provided with a spiral valve, and 

 in Hyrax, besides a large sacculated caecum at the junction of the 

 small and large intestines, there is a pair of large simple conical 

 caeca further back. 



Monotremes only amongst Mammals possess a proper cloaca, 



1 In Cetacea and Bradypus (Fig. 192, I) however, the stomach is divided into 

 several chambers, and in some Eodents and the Horse a distinct cardiac and a pyloric 

 division can be recognised : some Marsupials (e.g. Halmaturus) also possess a com- 

 plicated stomach. In Ungulates numerous forms between a simple and an exceedingly 

 complex stomach are to be met with. 



8 The psalterium is the latest to be differentiated, both phylo- and ontogenetically. 



