144 THE OSTEOLOGY AND MYOLOGY 



liomologue of the pronator teres can be found in the leg ; and the same may be said of the 

 supinator brevis. These two muscles, antagonistic in their action, appear as highly special- 

 ized developments, in the face of particular conditions necessary to the function of the 

 hand, and so far as known, are not developed in the posterior extremity, although they 

 would be looked for, if anywhere, in such a pedimanous animal as the opossum. The 

 homologue of the pronator quadratus, however, is present in the interosseus muscle of 

 the leg ; one having substantially the same position, relation and function. 



The supinator longus has been variously interpreted. Its insertion, in the human subject, 

 into the styloid process of the radius, makes it virtually a humero-cubital muscle ; and 

 Prof. Wilder regards it as an accessory short flexor of the forearm like the other supinator 

 and the pronator, and finds its homologue in the femoral head of the biceps cruris. With 

 him, I look upon its supinating action as purely secondary, recognizing only flexion and ex- 

 tension as the fundamental motions of the limbs ; but I conceive the muscle to belong to 

 the carpal set, and see in it a long, direct, radial extensor of the wrist (what would be a 

 ''flexor" in ordinary anatomical language), and consequently as only an indirect "short" 

 flexor of the forearm. For this, as w^ell as for reasons already given, I cannot see the 

 femoral head of the biceps in this homologue. In the opossum it goes to the wrist, not 

 to the end of the radius. Bringing the supinator longus into this connection, it results 

 that we have upon the radial side of the forearm four carpal muscles ; two extensors— 

 supinator longus and "flexor" carpi radialis; and two flexors— "extensor" carpi radialis 

 longior and brevier -, the homologues of which four are to be sought for in fibular, or out- 

 side muscles acting on the tarsus. 



Noticing the origins and insertions of the long supinator and radial "flexor" (extensor), 

 we find that the former arises from the outer, and the latter from the inner side or condyle 

 of the humerus, and that both are inserted at or near the outside bone of the proximal 

 carpal row— the scaphoid. In the leg there are two large extensor muscles, whereof one 

 arises from the outer, and the other from the inner, condyle of the femur ; and both pro- 

 ceed to be inserted by separate tendons into an outer bone of the proximal tarsal series 



the calcaneum. These two extensor muscles, the gastrocnemii, in the opossum instruct- 

 ively distinct from each other in origin, course and insertion, have precisely the same 

 relations in the leg that the supinator longus and "flexor " carpi radialis hold in the fore- 

 arm. If our osteological premises are correct — and there seems no good reason for doubt- 

 ing this — the gastrocnemius externus is the homologue of the supinator longus, and the 

 gastrocnemius internus is the homologue of the "flexor" (extensor) carpi radialis. 



Looking now to the other two of the four radio-carpal muscles, we find that the " ex- 

 tensor" (flexor) carpi radialis longior and brevier arise together or contiguously from the 

 outer condyle, Ke along the radial side of the fore arm, and are inserted by distinct tendons 

 into two contiguous parallel metacarpal bones — the second and third, counting from radial 

 to ulnar side. Similarly, there are in the leg two fibular tarsal muscles, arising, if not from 

 the outer femoral condyle itself, at least from the corresponding side of the leg, lying along 

 the fibula, passing behind the external malleolus (= head of the radius) to gain the back 

 and outer side of the tarsus, and finally proceed to a metatarsal insertion ; they are the 

 two larger peronei. The insertion of these muscles, however, does not, further than in 

 being metatarsal, correspond to that of the wrist muscles just mentioned, for instead of 

 going to contiguous second and third metatarsals, counting from without inward, one stops 



