xxviii. 2 UNGULATE CHARACTERS 697 



are numerous, so that the girder has large compression struts above 

 and below and it balances largely on the fore-legs and is pushed from 

 behind. The ilium is broad and raised vertically, providing large attach- 

 ments for the glutei, which are the important locomotor muscles, and 

 for the abdominal muscles, which carry the weight of the belly. This 

 arrangement of the column is essentially preserved even in the very 

 large animals, such as elephants, rhinoceroses, and many extinct types, 

 which are said to be 'graviportal'. In these latter, however, the legs 

 are arranged on a different plan, since the great weight can only be 

 carried by very massive struts of large cross-section. The proximal 

 parts are therefore enlarged and several digits are retained to make 

 broad supports for the pillars, as is well seen in the elephant's foot. 



In many ungulates the neck becomes considerably lengthened, 

 probably both in order to reach up or down for food and also to give 

 a good look-out for the head. The ears are long and hearing acute, so 

 that the direction of sounds may be easily detected. Sight is not especi- 

 ally developed, but the pupil is often horizontal in animals that live 

 on the plains, giving a wide visual angle. The sense of smell is well 

 developed and the animals often graze advancing up-wind, using 

 for this purpose the receptors of the moist muzzle. The tongue is large 

 and taste receptors sensitive. 



The brain is large and the life of these herbivores is conducted with 

 the use of much information learned during each lifetime. This 

 enables them to range over large territories and to vary these with the 

 seasons, in search of food and water. They show a remarkable alertness 

 to changes of sound or scent. 



Many herbivores are social animals, and information is shared 

 among a large group. They have elaborate means of communication 

 by scent glands, which are used to mark trails and territory, as well as 

 for exchange of signals between individuals. Their sexual organization 

 is complicated, involving elaborate interchange of visual, auditory, 

 and olfactory signals and often combat between males. The establish- 

 ment of a leader is apparently often needed to allow the advantages of 

 social organization for protection and finding food. Gestation is long 

 and relatively few young are produced (as in other large animals with 

 efficient brains). The new-born is well developed and soon able to run 

 with the herd. 



Perhaps the most significant modifications are in the means of 

 obtaining and digesting the food. The triangular molar pattern gives 

 place to a square one, by development of a hypocone on the posterior 

 interior side of the upper molar. The lower molar also becomes 



