424 LAND MAMMALS IN THE WESTERN HEMISPHERE 



normal mammalian fashion, but come in successively from 

 behind and the series moves forward, so that the foremost tooth 

 is pushed out, when it is so worn down as to be of no further 

 service. As these teeth are very large and the jaws are rela- 

 tively short, only one tooth on each side, above and below, is in 

 use at the same time, though part of a second may also be in- 

 volved. The movement of the successive teeth is not directly 

 forward, but oblique, an upper tooth coming forward and down- 

 ward and a lower tooth forward and upward. In consequence 

 of this arrangement the teeth are abraded obliquely, the anterior 

 part first coming into use, and, by the time a tooth is fully in 

 place, the front portion is worn down to less than half the 

 height of the hinder part. All of these peculiarities in the 

 dental system imply a very high degree of specialization and a 

 notable difference from other mammals. 



The skull is equally specialized, as is indeed required by 

 the character of the teeth and the development of the long 

 and heavy proboscis. The premaxillae are converted into 

 sheaths for the great tusks ; the nasals are extremely abbreviated 

 and the anterior nasal opening is shifted to the top, directly 

 above the posterior opening, so that the nasal canal passes 

 vertically downward through the skull. All of the bones 

 forming the cranium are enormously thickened and at the same 

 time lightened by the formation of an extensive system of 

 communicating sinuses, and thus the brain-chamber is, as it 

 were, hidden away in the middle of the huge mass of the skull. 

 This explains the difficulty of killing an elephant by shooting 

 it in the head ; the shot must be so directed as to reach the 

 brain, which requires knowledge and skill. 



The neck is short, the body long and extremely massive, 

 the tail of moderate length. The shoulder-blade is very large 

 and has a prominent metacromion given off from the spine ; 

 the hip-bones are immensely expanded in correlation with the 

 breadth of the thorax and abdomen. The limbs are long, 

 massive and columnar, their upper segments, especially the 



