35-2 TITE ANATOAIY OF TTTE TTOP.SE 



THE FORE AND HIND EXTREMITIES CON 

 SIDERED AS ORGANS OF LOCOMOTION 



Tin: sicvKUAL iKtNKS wliuh iuc runni'ctod to!,'i'tlicr t(i f<inii the cxtreiuitiea 

 must be regardotl, first, as ui'gaiis of support, and, secondly, as the primary 

 means of locomotion. Each extremity consists of corresponding divisions, 

 the ilium being the analogue of the scapula; the femur of the humerus; 

 tlie tibia and libula of the ulna and radius; the tarsus of the carpus; and, 

 lower down, the bones of the fore and hind extremities being precisely similar 

 in their forms. There is, however, a want of exact correspondence in the 

 form and direction of the joints, which has been nmcli insisted on by homolo- 

 gists, and which Mr. ^laclise has attempted to explain in his very interesting 

 article on "The Skeleton," contained in the Cydojia'dia of Anatomy and 

 Physioloyy edited by Dr. Todd. It appears to me that this does not make 

 matters niore simple, but the reverse, and that the proper point of view is 

 to regard the humerus and femur as homologous, and the tibia, with the 

 patella, as analogous to the ulna and its olecranon process. The interven- 

 tion of the ligament between the patella and tibia does not affect the use 

 of the former as a lever ; and botli joints being perfectly hinge-like in their 

 actions, there is no other important difference. Descending to the next 

 joint, the os calcis stands out as an important lever, and is represented in 

 the carpus by the os pisiforme (called by Percivall os trapezium), each 

 having important muscles inserted in their upper edges. It is true that 

 the one is an agcjit in what is called extension, while the other is engaged 

 in flexing tlie limb; but this is onl}' dependent upon the limit to motion 

 in either direction. Below the carpus and tarsus there is no necessity for 

 continuing the comparison. 



Reg.xrding the ltmbs as means op support, it must be remembered that 

 the fore-Jimbs are neai'er the centre of gravity, and, therefore, sustain more 

 weight than the hind. The fore-quarter is suspended between the bases of 

 the two shoulder-blades, chiefly by the serrati magni, and in such a way as 

 to require no sj^ecial muscular contraction. The four parts of which the 

 limb itself is composed being bent at various angles, are prevented from 

 giving way by the muscular actions of the extensors of the humerus and 

 ulna, the carpus (or knee) having little tendency to yield, and the pastern 

 being supported by the flexor muscles and suspensory ligament. The hinder 

 limbs, though sustaining less weight, are not so favourably circumstanced 

 for this purpose, the angles between their several parts being generally more 

 acute. But if these are attentively regarded, tliere is not so much dili'crence 

 as is generally supposed. Thus, the first joint, the iliofemoral, forms a less 

 acute angle than its analogue, the shoulder joint (see Fig. 1, n, m). Again, 

 though the stifle joint is considerably bent, it is not more so than the elbow 

 joint, which will be clear on comparing the two in the skeleton given at 

 page 348. The chief disadvantage sustained by the hind-limbs as means 

 of support will be found in the hock, as compared with the knee, the latter 

 being nearly straight, while the former is much bent : but as it has a long 

 lever to assist it (the os calcis), and as this is kept in position by the power- 

 ful iiamstriug muscles, each of which serves its pui'poses far more completely 

 tlian the flexor of the carpus inserted in the os pisiforme, it may readily be 



