OF DIDELPHYS VIRGINIANA. 



117 



larger, and is inserted, moreover, into the outside of the shaft of the ulna for nearly an inch 

 below the olecranon. Some fibres of the conjoined triceps tendon are continuous with the 

 slip from the latissimus dorsi, and the fascia of the forearm. 



The forearm is very like our own in contour ; pronation and supination are perfect ; and 

 almost all the muscles of anthropotomy are present, with much the same relative size, shape, 

 position and action ; certain of them, however, differ a little in their insertion. No mar- 

 supial, perhaps, has a more perfect "hand" than the opossum. The fingers are very mobile, 

 and the thumb perfectly opposable. The most notable muscular absentees are the extensor 

 secundi internodii pollicis, and the flexor longus poUicis. 



In the supine forearm three muscular regions, containing as many sets of muscles, may 

 be conveniently, if artificially, distinguished. First, the radial, containing the long and 

 short supinators, and long and short radial wrist exten- 

 sors ; second, the anterior brachial, containing the round 

 and square pronators, sublime and profound digital flex- 

 ors, and long palmar ; third, the posterior brachial, con- 

 taining the ulnar wrist extensor, common digital extensor, 

 extensor of little finger, extensor of index and first 

 pollical internode, and extensor of pollical metacarpal. 

 Notwithstanding the number and variety of the extensors, 

 the flexor system, as usual, greatly preponderates in 

 power. 



Supinator longus. — (Fig. 29, g, and fig. 30, a.) 

 Largest of the four muscles of the region, arising high- 

 est up on the condylar ridge, and mainly determining the 

 contour of the parts. A somewhat flattened spindle with 

 thick fleshy origin, narrowing midway or at the lower 

 third, to a rounded tendon that passes over the head of 

 the radius to be inserted into the corresponding side of 

 the wrist. 



Supinator brevis. — There is no large muscle curving 

 over the upper third of the radius from the humeral con- 

 dyle and ridge of the ulna, as in man. The homologue 

 of the short supinator is found in a small, slender fascic- 

 ulus, about an inch long, that arises from the outer 

 condyle, or rather from the contiguous part of the joint- 

 ligament, in intimate relation with the head of the radius, 

 and lies upon, and is attached to, that bone, as far down 

 as the insertion of the pronator radii teres. It has a 

 fascial investment, and is perfectly distinct from the 

 superincumbent muscles. 



Extensor carpi radialis "loiigior." — (Fig. 29, h, and fig. 30, b.) Arises from the ex- 

 ternal condylar ridge next below, and partly overlapping the S. longus, lying in its 

 whole length between this and the muscle next described. It bears the same general 

 characters as the long supinator ; its tendon passes, in company with the tendon of the 



Fig. 29. — ^Muscles of the right foreariu, 

 anterior surface; natural size. 



MEMOIRS BOST. 800. NAT. HIST. VOL. II. 



