752 ARTIODACTYLS xxxi. 6- 



of hump. When wild they are mainly mountain-dwellers. The spitting 

 of the llama is a protective device, the whole contents of the stomach 

 being thrown at the attacker! 



The Tylopoda show some features retained from the Eocene condi- 

 tion, some developments parallel to those found in the Ruminantia, 

 and various special features of their own, the latter mainly in charac- 

 ters that suit them for life in sandy desert conditions. In the limbs 



Fig. 499. Skeleton of dromedary. (From Owen, The Anatomy of Vertebrates, 

 Longmans, Green & Co.) 



(Fig. 499) there has been complete loss of the lateral digits and of some 

 carpals and tarsals, but not the fusion of navicular and cuboid that is 

 so characteristic of the Pecora. A specialized feature is the loss of the 

 hoofs. They were present in early camels but are replaced in modern 

 forms by a nail and large pad. The toes thus spread sideways and en- 

 able the animals to walk on soft or sandy ground. The large hump of 

 fat on the back provides water as well as calories when metabolized. 

 The ruminating mechanism is different from that of the Pecora and 

 simpler (Fig. 491). 



The wall of the rumen contains a number of pockets separated by 

 muscular walls. These are usually called water pockets and have been 

 supposed to have a storage function, with sphincters. However their 

 walls are glandular and their function may be digestive. There is no 

 external separation of omasum and abomasum, which form a single 



