THE HUMAN I'UAlMi:. 475 



Man presents the only instance among the mam- 

 malia of a conformation by which the erect posture 

 can be permanently maintained, and in which the 

 office of supporting the trunk of the body is con- 

 signed exclusively to the lower extremities. To 

 this intention the form and arrangement of all the 

 parts of the osseous fabric, and the position and 

 adjustments of the organs of sense have a well 

 marked reference. 



In most quadrupeds, as we have seen, the thorax 

 is deep in the direction from the sternum to the 

 spine, but is compressed laterally, for the evident 

 purpose of bringing the fore limbs nearer to each 

 other, that they might more effectually support the 

 anterior part of the trunk. In Man, on the con- 

 trary, the thorax is flattened anteriorly, and extends 

 more in width than in depth ; thus throwing out 

 the shoulders, and allowing an extensive range of 

 motion to the arms. 



The lower limbs are qualified to be the efficient 

 instruments of progression by their greater length 

 and muscularity, compared with the generality of 

 quadrupeds. The only exceptions to this rule occur 

 in those mammalia which are constructed expressly 

 for leaping, such as the Kanguroo and Jerboa, 

 where, however, the hind legs are employed almost 

 solely for that mode of progression. The Quad- 

 rumana, which come nearer to the human form 

 than any of the other tribes, have the lower limbs 

 comparatively weak. In almost all other quadru- 

 peds the disproportion is still greater, the thigh 

 being short, and almost concealed by the muscles 

 of the trunk, and the remainder of the limb being- 

 slender, and not surrounded by any considerable 

 mass of muscles. 



