712 



ELEPHANTS 



xxix. 4 



seven separate 'plates', which develop as separate cones of dentine 

 and enamel, each with its own pulp cavity, the cones being finally 

 joined together by cement. The teeth are placed just above the 

 ascending ramus of the mandible, so that the large jaw-muscles work 

 at maximum advantage. For their attachment the skull becomes 

 extremely short and high, with the development of large air spaces 



Fig. 475. Skeleton of an Indian elephant. (From Owen, The Anatomy of Vertebrates, 



Longmans, Green & Co.) 



between its tables. This shape also allows a large occipial region for 

 the muscles that hold up the head. 



With this head structure the elephants have been able to grow to a 

 size that must approach the limit possible for a fully terrestrial 

 animal. The backbone (Fig. 475) is based on a 'single girder' plan, 

 with as many as twenty ribs, and high thoracic neural spines, forming 

 together a huge beam that carries the weight of the abdomen and 

 balances it on the fore-legs against the weight of the head, the hind- 

 legs acting as propellents. The ilium is nearly vertical and expanded 

 transversely for the attachment of the large gluteal, iliacus, abdominal 

 and sacrospinalis muscles. The acetabulum faces downwards. 



As in other heavy animals the legs are enormous pillars, with long 



