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ANATOMY OF PHAL^NOPTILUS, RIDGWAY. 229 



extensor digitorum profundus to the antero-ventral surface of the 

 third metacarpal, runs along the anterior rim of the first phalanx of 

 third digit, and is inserted on the proximal end of the second pha- 

 lanx about one third its length from the proximal end. The ante- 

 rior tendon continues to the wrist where it merges into a tendin- 

 ous band which extends from the ventral edge of the styloid proc- 

 ess of the radius to the anterior border of the os ulnare. From 

 this latter point come off two other tendons, the upper and more 

 delicate being inserted at about the mid-point on the ventral bor- 

 der of the third metacarpal. The thin, flat, posterior tendon runs 

 along the ventral surface of the fourth metacarpal and is attached 

 near its distal end. The insertion is quite different from the de- 

 scription of Gadow (/. c. ). 



15. M. flexor digitorum profundus {F. dig. p., PL V, Fig. 24). 

 This muscle arises fleshily from the proximal half of the ventral sur- 

 face of the ulna. Proximally it is divided into two almost equal 

 portions by the brachialis inferior which inserts on the ulna between 

 them. The surface of origin gradually diminishes and ceases alto- 

 gether when the broad expansion of the ulni metacarpalis ventralis 

 is reached. At the wrist the tendon runs under the tendinous 

 band of the m. flexor digitorum sublimis, passes above the ventral 

 projection on the proximal end of the third metacarpal, and is here 

 held in place by a ligament extending from this projection to the 

 distal ventral edge of the radius. It is inserted on the antero- 

 ventral rim of the proximal end of the second phalanx of the third 

 digit. 



16. M. extensor digitorum communis {Ex. dig. c., PL V, Fig. 

 22). This fusiform muscle arises by a short tendon from the ex- 

 ternal condyle of the humerus between the tendons of origin of the 

 m. extensor metacarpi ulnaris and m. ectepicondylo radialis. The 

 muscle becomes tendinous at about two thirds the length of the 

 radius. Soon after passing the ulna the tendon bifurcates, sending 

 a delicate slip to the pollex digit, inserting about one third the 

 length of that bone from its proximal end. The long fork is twice 

 crossed by the tendon of the m. extensor indicis longus and is finally 

 inserted on the proximal rim of the first phalanx of the third digit. 



17. M. extensor pollicis longus (E.pl. /., PL V, Figs. 19, 22). 

 Covered by the m. extensor indicis longus, the muscle comes from the 

 facing surfaces of ulna and radius, from the proximal third of the 



