o/" Cyclothurus didactyliis. 251 



of the axillary costa of the scapula, just posterior to the glenoid 

 cavity, and joins that portion of the muscle which rises from 

 the humerus. This latter portion is bifid at origin, the mus- 

 culo-spiral nerve passing between the two heads, one of which 

 arises from the posterior surface of the shaft of the humerus, 

 as high up as the neck of the bone, while the other takes 

 origin immediately behind the insertion of the deltoid, and is 

 joined by the " long " head. 



From that portion of the humerus which answers to the 

 olecranon-fossa of human-anatomy language arise some fibres 

 (anconeus) which join the main body of the muscle. These 

 are limited above by the musculo-spiral nerve, from which 

 they receive a special branch. The insertion of the tricejjs 

 was as usual. 



There was a well-developed epitrochleo-anconeus, passing 

 from the internal condyle to the olecranon, and having the 

 usual relation to the ulnar nerve. 



The supinator longus was well developed. It arose from a 

 ligament stretched between the deltoid tubercle and the " su- 

 pinator ridge" of the humerus. Before reaching its insertion 

 it separates into two strata, the lower of which terminates at 

 the distal extremity of the radius, while the upper is lost in 

 fascia covering the inner and dorsal aspects of the wrist, and 

 also joins obliquely the anterior annular ligament of the carpus. 

 The lower layer seems to be in its turn differentiable into two 

 strata. To the muscle is distributed branches from the poste- 

 rior interosseous nerve, just anterior to the emergence of the 

 musculo-spiral nerve from beneath the ligamentous bridge 

 mentioned above. 



The upper stratum of the supinator longus is thus described 

 in the explanation of Cuvier's plates : — " Muscle propre (G. 

 Cuvier) c'est un 2^ long supinateur " (pi. 257. fig. 1, & pi. 258). 



The supinator brevis was also well developed. It arose 

 from the external condyloid ridge of the humerus, covered by 

 the origins of the common extensor and of the extensor ossis 

 metacarpi pollicis, and was inserted along the whole of the 

 outer edge of the radius, coextensively with the radial origin 

 of the flexor profundus. The muscle was pierced at its origin 

 by the posterior interosseous nerve. 



The extensor carpi radialis arises from the humerus, imme- 

 diately below the supinator longus. It is a large, but single 

 muscle. It becomes tendinous at the distal third of the fore- 

 arm ; and the tendon passes under a ligamentous pulley at the 

 wrist-joint, to be finally inserted into the radial side of the 

 third metacarpal bone, being previously crossed by the " dorsal 

 interosseous " .muscle (Cuv.), which passes to the terminal 

 phalanx of the index. 



