110 TRE BONES. 



being nearer the centre of gravity than those behind, have to sustain the 

 largest share of the weight. They ought, consequently, to be specially 

 organised as organs of support. Therefore it is that the four principal rays 

 composing each of them — shoulder, arm, fore-arm, and foot — although flexed, 

 or disposed to be flexed, in an inverse sense to one another, oppose to the 

 pressure of the weight of the trunk, which tends incessantly to throw them 

 down, obstacles purely mechanical, and of such energy that we may still 

 understand how the body can be sustained on the anterior limbs, if we 

 suppose all the muscular masses surl'ounding these bony rays removed except 

 one. 



Thus, the weight of the body is at first transmitted to the scapula through 

 the muscles that attach that bone to the trunk. It then passes to the 

 humerus, and from thence to the radius, to be thrown, finally, on the different 

 pieces composing the foot. Now the humerus forming with the scapula an 

 angle which is open behind, and with the bones of the fore-arm another angle 

 open in front, the weight of the body pressing continually on these angles tends 

 "to close them, and thus cause the flexion of the bony i-ays. But this result is 

 prevented by the combined action of two muscular powers — the biceps and 

 the extensors of the fore-arm. With regard to the radius, carpus, and 

 metacarpus, owing to their vertical direction they themselves support the 

 pressure of the weight of the body without requiring any muscular aid. But 

 the digital region, being directed obliquely forward and downward, forms, 

 with the principal metacarpal, a third angle open in front, for the sustenance 

 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 extremity. 



The posterior limbs are less favourably disposed than those in front to 

 assume 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 (See Figs. 1, 2, 3, 4, 

 5). It is therefore necessary that muscular agency should prevent the 

 breaking-down of these rays. Though defective as supporting columns, 

 they are nevertheless admirably designed to serve as agents of locomotion. 

 The slightest erection of these inclined rays propels the mass of the body 

 forward, 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 Antbkior 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 impulsive agents in the locomotory acts. 



Notwithstanding this difference in the functions assigned them, these two 

 columns offer in their conformation such striking resemblances to each other, 

 that some authors have been inclined to consider the posterior as an exact 

 repetition of the anterior limb. The following is a brief analysis of the 

 analogies existing between them. 



At the end of the last century, Winslow and Vicq-d'Azyr, and nearer our 

 own time, Cuvier, Flourens, Paul Gervais, Martins, Gegenbaur, and Lavocat, 

 have occupied themselves with the parallelism existing between the anterior and 

 the posterior members. All these anatomists did not absolutely arrive at the 

 same conclusion ; for several of them, forgetting that the question should be 

 examined in the whole animal series, made Man alone the subject of their 



