386 THE ANATOMY OF VEETEBRATED ANIMALS. 



narrow moutlis, are developed. Tliese, the so-called " water 

 cells," sei-ve to strain off from the contents of the paunch, 

 and to retain in store, a considerable quantity of water. 

 The reticulum is sharply defined from the rumen, and com- 

 municates with it by a comparatively small aperture. The 

 oesophageal groove is bounded by only one ridge, which lies 

 ujDon its left side. The psalterium is reduced to a mere 

 tubular passage, without lamiuas ; and the abomasiim is 

 large, and has the ordinary structure. The pyloric end 

 of the duodenum is considerably dilated, and has been 

 taken for a division of the stomach. The ccecum is short 

 and simple. By a remarkable exception among the Mam- 

 malia, the red blood corpuscles are elliptical. The fcetal 

 villi are scattered evenly over the chorion, so that the 

 placenta is diffuse. 



"While the Trac/ulidce connect the typical Ruminants with 

 the non-ruminant Ai-tiodactyles, the Camelidce, on the 

 other hand, link them with Macrauchenia and the Perisso- 

 dactyles. 



The Camelidce are at present represented by two very 

 distinct groups — the Camels of the old world and the 

 Llamas of the new. They occur in the fossil state as far 

 back as the miocene epoch. 



II. The ToxoDONTiA. — This order has been founded for 

 the reception of the large extinct Mammal ( Toxodon), remains 

 of which have been discovered in the later tertiary deposits 

 of South America. 



Tlie supraoccipital siu-face of the massive skull slopes 

 obliquely upwards and forwards. There are supraorbital 

 jjrolongations. The zygomata are very strong and arched, 

 and the bony palate is very long. 



In the upper jaw there are two small, inner, and two 

 large, outer, incisors. In the lower jaw there are six incisors. 

 In tfce mandible there are canines in the middle of the in- 

 teiwal between the incisors and the grinders. In the upper 

 jaw of the adult, only indications of the former existence of 

 alveoli for canines remain. The grinding teeth are seven 

 on each side above, and six on each side below. They are 



