1392.] The Contemporary Evolution of Man. 473 



reverting to its former function of flexing the fingers by 

 insertionjin the metacarpals. 



The rise of muscular specialization by degeneration is 

 beautifully shown in the extensor indicis, which, while nor- 

 mally supplying the index only, revert- by sending its former 

 slips to the thumb, middle, and even to the ring finger. 

 Testut 1 believes that the extension power of the middle and 

 ring fingers has declined, as the cases of reversion point to 

 greater mobility ; the extensor minimi digiti is distinct and 

 highly variable (Wood), often sending a slip to the ring hng.-r. 



The entire flexor groupof the hand, excepting the palmarw, 

 is apparently specializing. The demonstration by Windl.- 1 

 and Bland Sutton, that the origin of the flexors and entensors 

 is sniffing downward from their original position, is evidence 

 of an adaptation to the short special contractions required oi 



1 The abductor pollicis* is also progressive and ramble 

 (Wood); the reduplication of its inferior tendon, which is 

 sometimes provided with a distinct muscle, apparently pointe 

 to the birth of a second abductor. The opponens of I 

 is well established and constant. ^ anabilm seems to . haiae- 

 terize both the developing and degenerating muscles, tne 

 latter are apt to be absent; it is rare that an important mus- 

 cle, such as the extensor indicis, is absent, but such cases are 



Til interesting to note that the lost muscles of the body 

 are almost exclusively in the trunk or shoulder a: 

 arches, and not in the limbs. It will be remember! tl 1, 

 human shoulder-joint is excepl 

 quadrupedal state it was a factor m progivs-.o... 



muscular reversions in this quadrupedal n B 

 clavicnlB3(l to 60, Macalister), trachelo- 



intermedins, acromio-basilari- 



(Gegenbaur). Apparently associated with he™ t 



ng g f the body by the fore-limb in the arboreal life are the 



journal of Anatomy a 



