582 MR. J. C. GALTON ON THE MYOLOGY OF 



• brid 



articulation of the foot, splits into two branches, which terminate at the ungual phalanges 

 of the " fifth " and " fourth " digits respectively. The radial tendon also splits into two 

 branches, at a similar articulation to that at which the ulnar divides, which terminate 

 respectively at the ungual phalanges of the index and "middle" digits. 



The radial branch of the muscle, moreover, detaches from its ulnar side, on becoming 

 tendinous, a somewhat slight tendinous slip, which passes to a short transverse band, by 

 which the ulnar and radial tendons communicate before they each split into two branches. 



The somewhat slender tendon of the extensor indicis passes beneath the tendons of the 

 extensor communis as they run under the bridge formed by the annular ligament ; and the 

 radial branch of the extensor annularis, which passes to the middle digit, appears to com- 

 municate with the inferior surface of the ulnar tendon of the extensor communis. 



Cuvier represents this muscle as giving off, upon its emergence from under the terminal 



expansion of the supinator longus, three equal-sized tendons, which pass to the index, 



"middle," and "annularis" digits respectively 1 . 



In Prof. Humphry's specimen 2 there were "four tendons derived from two bundles of 

 muscle," &c. 



Extensor annularis. — Arises from the upper portion of the external condyle of the 

 humerus, immediately below, and in conjunction with, the common extensor. It then 

 runs between this muscle and the extensor minimi digiti as far as the beginning of the 

 carpus, and becomes tendinous at the level of the carpo-metacarpal joint of the digit 

 from which it derives its name, and at this point runs under a delicate ligamentous 



- 



The tendon then passes under the ulnar division of the common extensor tendon, 

 dividing here into two branches, one of which passes to the ulnar side of the base of the 

 proximal phalanx of the third (" middle") digit ; while the other courses along the ulnar 

 side of the fourth (" annularis") digit, and, after sending downwards an offset at the leve 1 

 of the base of the proximal phalanx, which is joined by an interosseus muscle occupying 

 the intermetacarpal space between the fifth and the above digit, is continued onwards to 

 the base of the distal phalanx 



Cuvier represents 3 the tendon of this muscle as dividing into two branches, the radial 



of which passes beneath the ulnar division of the common extensor tendon to the ulnar' 



side of the "middle" digit; while the ulnar branch runs to the "fifth," and not to the 

 "fourth" digit. 



Neither the branch to the "middle" digit nor the communication with the interosseus 

 appears to have existed in Prof. Humphry's specimen 4 . 



I have described a muscle similar to the above as present in Dasypus sexcinctus. 



Extensor digiti mmimi.~A fusiform muscle, which arises from the external face of the 

 outer tuberosity of the humerus, immediately below the orisrin of the extensor annularis 



and above that of the extensor carpi ulnaris, with which muscle it is fused for the first 

 halt of its course. It does not become tendinous till it nearly reaches the extremity of 

 the ulna ; here its tendon passes to the radial side of a tubercle which lies at about the 



1 Anat. Comp. pi. 254. fig. 2. 

 3 Op. cit. ibid. 



2 hoc. cit. p. 307. 

 4 Loc. cit. p. 307. 



