16 STUDIES IN COMPARATIVE ANATOMY. 



passes beneath extensor pollicis, and has a distinct sheath upon 

 the lower end of the radius ; crosses the carpus, and is inserted 

 principally into the base of the metacarpal of the 3d digit, and 

 partly into the metacarpal of the 2d. 



C. and L.— 274-5 (S^) ; 276-7 (S^) ; 283, figs. 1, 2 (S^) ; 284, 

 fig. 1 (SI). 



Extensor communis digitorum arises by fleshy and tendinous 

 fibres from the lower part of the external condyloid ridge, on the 

 outer side of extensor carpi raclialis, and also from the outer side 

 of the external condyle, the two portions being indistinctly sepa- 

 rated by a septum. The muscle passes down in a special sheath 

 over the end of the radius, and becomes tendinous opposite the 

 wrist-joint. The tendon spreads over the carpus, and is finally 

 inserted into the upper surface of the 2d, 3d, 4th, and 5th digits. 

 The divisions of the tendon of insertion form arches beneath 

 which the vessels appear, as in the pes. 



C. and L.— 274-5 (e) ; 276-7 (e) ; 284, fig. 1 (e). 



Extensor minimi digiti arises by two heads — one muscular, 

 and the stronger of the two, from the outer surface of the ex- 

 ternal condyle ; the other, which is smaller and tendinous, from 

 the front and outer side of the head and shaft of the ulna, and 

 from an intermuscular septum between it and extensor carpi 

 ulnaris. The muscle passes through a distinct sheath on the 

 back of the ulna to the outer side of the manus, crossing the 

 insertion of extensor carpi ulnaris, and is inserted into the base 

 of the 5th digit. A tendinous expansion passes from the fore- 

 part of the tendon to the outer side of the base of the 1st 

 phalanx of the 4th digit, and blends with the deep surface of 

 extensor communis. 



C. and L.--274-5 (e^) ; 276-7 (e^) ; 284, fig. 1 (e^). The addi- 

 tional slip of insertion is shown as passing to the 3d and not to 

 the 4th digit. 



Extensor carpi idnaris, a strong muscle arising by a round 

 tendon from the external condyle of the humerus, behind and a 

 little above extensor minimi digiti. It lies along the outer sur- 

 face of the ulna, passes through a distinct sheath on the outer 

 side of the lower extremity of that bone, and is inserted by a 

 strong round tendon into the metacarpal of the 5th digit. 



C. and L.— 274-5 ; 276-7; 284, fig. 2 (/3i). 



