Vice-President's Address. 13 



muscle is thin and comparatively feeble, and the posterior 

 interosseus nerve passes from the front of the arm to the 

 back of the forearm lying exposed upon the surface of the 

 muscle. In man the same muscle is of much greater strength 

 and importance, and it has acquired an extended surface of 

 origin by utilising its investing fascia for this purpose, with 

 the result that the posterior-interosseous nerve is no longer 

 found upon the free surface, but is buried in the substance of 

 the muscle in its passage from the front to the back of the 

 limb. Further evidence of a similar kind is found in con- 

 nection with all the muscles of the human thumb. Its long 

 flexors and extensors have attained a completeness and a 

 proportion not seen in any of the apes. 



In the hand, the same may be said of the adductor pollicis 

 muscle, whose magnitude and complexity entirely surpass 

 those of the corresponding muscle among apes. Simul- 

 taneous with this gain as regards the thumb, there has been 

 a corresponding loss as regards the other digits, for while 

 among apes there are also adductor muscles (often called 

 Contrahentes) for the index, ring, and little fingers, which 

 are probably of value in certain movements of the hand 

 associated with its function of acting as a support for the 

 body by resting upon the knuckles, these adductors have 

 entirely disappeared from the human hand, in view of the 

 entire freedom of digital movement resulting from its libera- 

 tion from the function of supporting the weight of the body 

 in the act of walking, and the increasing importance of the 

 thumb. Concurrently with the growth of the adductor 

 pollicis there has been a dwindling of the interosseous primus 

 volaris, which is not unfrequently almost entirely absent. 



In the face and neck the imperfect sheet of muscle which 

 is concerned in the general question of facial expression, pre- 

 sents evidence of a former much more extensive distribution 

 in the possession of a motor nerve-supply to all appearance 

 greatly in excess of its apparent needs. This is more especially 

 visible in connection with the muscles which are intended for 

 the movements of the pinna, and with the platysma myoides 

 in the neck. Similarly, it is difficult to see the association of 

 the stylo-hyoid and the digastric (posterior belly) muscles with 



