6 ON THE STRUCTURE AND 



through the air. They are generally shorter and more weak 

 than the hind-legs; and in some of the animals, as the Kan- 

 guroos and Jerboas, they are so extremely short, as scarcely 

 to be of any use in walking. In the long-armed Ape, and 

 the Giraffe, their length is, however, considerably greater 

 than that of the hind legs. 



With respect to the posterior extremity of quadrupeds, 

 the two hips, united into the pelvis, serve as a support to the 

 intestines. Into a hollow in each of the hips is articulated 

 the head of the thigh bone. This bone is single ; but the 

 leg, which extends from the joint of the knee to the foot, 

 has two bones, the larger called the tibia, and the smaller, 

 (which is on the exterior side of this,) denominated the 

 fibula. Over the articulation of the thigh bone with the 

 tibia, in some of the animals, there is -a little bone, almost of 

 a circular shape, but somewhat pointed below, placed for 

 the purpose of preventing the tibia from being extended in 

 front beyond a right line. This is called the patella, and is 

 the bone that forms the angle of the knee. The ancle and 

 the foot have a general resemblance in their external ap- 

 pearance, and in their uses, to the wrist and hand . The toes 

 of all the feet are armed, at their extremities, either with 

 nails or claws, or are enveloped in hoofs. A few of the 

 animals, as the Seals and Otters, which live much in the 

 water, have their toes connected together by strong mem- 

 branes, to serve the place of fins or oars in swimming. 



In addition to the preceding four extremities, most quadru- 

 peds have a tail, or fifth extremity. The Apes, some of the 

 Bats, the Guinea-pig, and some others, are, however, en- 

 tirely destitute of this member. It seems given to them chief- 

 ly to serve the purpose of a whip, to drive away some of 

 those swarms of insects with which, in hot climates particu- 

 larly, they are often teased; and also as a covering, to 

 guard the posterior parts of their body from injury. In a 



few 



