INTRODUCTION. 



And here it may be observed, that the human thorax, or chest, is of 

 much greater breadth than depth, while that of quadrupeds is laterally 

 compressed ; hence, their fore limbs more closely approximate, and, con- 

 sequently, afford a much more efficient support to the anterior part of the 

 trunk than they would, if as widely separated as in Man : on the other 

 hand, the great transverse dimension of the human thorax necessarily 

 demands a corresponding distance between the shoulders, by which the 

 arms enjoy greater freedom of motion than in quadrupedal Mammalia ; 

 while, at the same time, the anterior preponderance of the trunk is 

 diminished, so as to harmonize with the structure of other parts of the 

 frame, by which Man is adapted for a vertical attitude. In this posi- 

 tion the weight of the abdominal viscera falls chiefly upon the pelvis ; 

 but, in quadrupedal Mammalia, the case is very different ; and, there- 

 fore, in order to sustain the viscera, the body being in a horizontal 

 position, the sternum, compared with that of Man, is much elongated, and 

 the ribs are, for the same purpose, not only often more numerous than in 

 the human skeleton, but more nearly approach the pelvis ; so that, toge- 

 ther, they contribute to the support of the abdominal viscera, and this, 

 more particularly in the Ruminantia and Pachydermata, as is well exem- 

 plified in the skeleton of the Elephant (fig. 58). 



The third division of the vertebral column begins with the vertebra 

 succeeding the one to which the last false rib is articulated, and ends at 



