THE LIMBS IN GENERAL AND THEIR PARALLELISM. 



155 



forearm. With regard to the radius, 

 carpus, and metacarpus, owing to their 

 vertical direction, thej themselves sup- 

 port the pressure of the weight of the 

 body without requiring any muscular 

 aid. But the digital region, being di- 

 rected obliquely forward and downward, 

 forms, with the principal metacarpal, a 

 third angle open in front, for the main- 

 tenance of which nature has given solid, 

 inert, or contractile mechanical bands. 



The anterior limbs are also agents 

 of transport, for they can elevate the 

 trunk by the spring of their bony rays, 

 and fix themselves on the ground by 

 their free extremities. 



The posterior limbs are less favour- 

 ably disposed than those in front to as- 

 sume the function of columns of support ; 

 as their rays are, for the most part, in a 

 state of permanent flexion, and joined in 

 an angular manner to one another, as 

 may be seen by glancing at the skeleton 

 (Figs. 107, 108, 1, 2, 4, 5, 6). It is, 

 therefore, necessary that muscular agency 

 should prevent the breaking-down of 

 these columns. Though defective as 

 supports, they are nevertheless admirably 

 designed to serve as agents of locomotion. 

 The slightest erection of these inclined 

 bones propels the mass of the body for- 

 ward, and this impulsion is almost wholly 

 transmitted to the trunk, in consequence 

 of the very intimate union of the pelvis 

 with the vertebral column. 



B. Parallel between the An- 

 terior AND Posterior Limbs. — After 

 what has just been said, it will be seen 

 that the anterior limbs are more par- 

 ticularly destined for the support of the 

 body, while the posterior ones more 

 especially play the part of propelling 

 agents in the locomotory acts. 



Notwithstanding this difference in 

 the functions assigned them, these two 

 limits offer in their conformation such 

 striking resemblances to each other, that 

 some authors have been inclined to con- 

 sider the posterior as an exact repetition 

 of the anterior limb. The following is 



Fig. 107. 



ANTERIOR LIMB OF THE HORSE (AHTEBO- 

 KXTERNAL VIEW). 



0, Scapula ; n, liumerus ; A, radius ; C, carpus ; 

 M, metacarpus ; p, phalanges ; 8, sesamoid 

 bone. 1, Coracoid process ; 2, head of the 

 humerus; 3, external trochanter ; 4, deltoid 

 ridge ; 5, inferior articular surface of the 

 humerus; 6. olecranon; 7, ulna; 9, pisi- 

 form (trapezium), or supercarpal bone. 



