398 Harris Hawthorne Wilder, 



mass terminates at the base of the metacarpals in a "Sehnenwulst", froro 

 which four flat tendons run to the four fingers, "außerdem aber kurze 

 Faserzüge sich seitlich auf die Basis der Metakarpalien, auch der mar- 

 ginalen, heften". These "Faserzüge", which prolong the tendons laterally, 

 convert the latter into the "Dorsalaponeurose" of Osawa, although ErSLEK 

 says nothing of the participation of other muscles in its formation. 



B.IBBING, 1906, perhaps the most recent writer on the subject, des- 

 cribes in the Axolotl (Siredon) an interesting condition in the "langer 

 Streckmuskel" of the arm, which may serve as a link between the con- 

 dition in Necturus, where the muscle stops at the bases of the metacarpals, 

 and that of Cryptobranchus, where the partly differentiated tendons of the 

 dorsal aponeurosis form its extension to the terminal digits, for here the 

 muscle, which involves only digits III — V, "inseriert mittels kurzer Sehnen- 

 zipfel an den Bases der Metacarpalia III — V U nd hat auch schwache 

 Verbindungen mit den kurzen Extensoren der 3 ulnaren Finger [die 

 kräftigste dieser Verbindungen ist die mit den kurzen Extensoren (dem 

 kurzen Extensor?) des 5. Fingers]". This condition, which incorporates 

 the short extensors and their tendons with the humerometacarpalis , may 

 be easily derived from that in Necturus, through a closer attachment be- 

 tween the terminal lips of the latter and the origins of the former, a con- 

 dition almost realised in the corresponding muscle of the Necturus foot, 

 where the connection between the two muscles is very close. 



The next logical step would seem to be the complete suppression of 

 the extensores breves as independent muscles, and the employment of their 

 tendons by the Compound muscle while the lateral tendons to the bases 

 of the metacarpals are still retained. This stage corresponds exactly to 

 ElSLElt's description of the condition in Salamandra , where the muscle 

 splits in the carpal region into three bundles "die je eine lange Sehne für 

 die Endphalangen der drei ulnaren Finger bilden, daneben aber noch 

 jederseits (an Dig. V. nur radial) Sehnenzipfel zu den zugehörigen Meta- 

 carpalbasen schicken". 



Although the idea of a gradual differentiation in this muscle within 

 the group of urodeles seems to be expressed in the writings of recent 

 investigators, such does not seem to have been the thought of the earlier 

 writers, who seem to have taken it for granted that a typical extensor 

 would be found in all cases. Thus Hoffmann, 1878, although he had 

 before him the work of Humphrey, describes this muscle, under the 

 name of M. humero-digiti II — V, as dividing "in vier Sehnen für die vier 

 Finger, an deren Endphalanx sie sich inserieren". As examples of this 

 condition he gives Menobranchus, Cryptobranchus, Siredon and Salamandra. 



The corresponding muscle of the foot, M. femoro-metatarsalis, is like 

 the humero-metatarsalis and its gradual evolution through the Order of 

 Urodela seem also to be the same. 



M. extensor radialis (er). This is the very large mass of 

 muscles which lies on the radial side of the forearm, partly covered 

 by the humero-metacarpalis. After the removal of the latter it is 

 seen to almost entirely cover the dorsal surface of the radius and 



