316 



MAMMALIA. 



R 



rangular crown has four chief prominences, which are separated 

 by deep valleys, which are not filled with cement, but are sometimes 

 furnished with small accessory protuberances. The prcemolars are 

 small, and have usually only one or two protuberances. The meta- 

 tarsal and metacarpal bones are always ankylosed, to form a cannon 

 bone (fig. 670d). 



The Ruminantia are characterised physiologically and anatomically 

 by rumination and by the structure of the stomach and dentition which 

 is correlated with this peculiarity. The food always consists mainly 

 of vegetable substances, which contain only a small portion of albu- 

 minous matter, and must, 

 therefore, be eaten in great 

 quantities. In this relation, 

 the division of labour be- 

 tween the acquisition and 

 reception of food on the one 

 hand, and its mastication on 

 the other, is an advantageous 

 arrangement, which is fore- 

 shadowed by the structure 

 of the stomach of other Mam- 

 malia. The animal plucks 

 and swallows its food while 

 moving freely from place to 

 place, and chews and masti- 

 cates it when at rest. 





Fio. 691-Stomach of a Calf. *, Pauntih or 



rumen ; E, Reticulum ; O, Manyplies or psalter- act of rumination depends 

 iuni; A, Abomasum or rennet stomach: Oe, End , . , -, 



of oesophagus: OE, (Esophogeal groove; D, be- ll P 0n the Complicated StrtlC- 



ginning of intestine. ture of the stomach, which 



is divided into four, more rarely into three, peculiarly connected 

 divisions (fig. 694). The superficially masticated, coarse food passes 

 through the lateral opening of the cesophageal groove, the lips of 

 which are separate from one another, into the first and largest division 

 of the stomach the paunch, or rumen (fig. 694.2?%). Thence it passes 

 into the small reticulum (R), a small rounded appendage of the rumen, 

 which receives its name from the net-like folds of its inner surface. 

 After the food is softened by the secretion which is poured into this 

 division of the stomach, it ascends by a process resembling vomiting 

 through the oesophagus into the mouth, and there undergoes a second, 

 more thorough mastication ; it is then returned in a semi-liquid form 

 through the cesophageal groove, which is now closed by the coming 



