122 PHYSIOLOGICAL SERIES. 



smaller muscle (supracoracoideus) that arises from the 

 sternum beneath the pectoralis major, passes as a tendon 

 over the point of the shoulder to its dorsal surface in a 

 canal formed by the union of the three bones of the 

 shoulder-girdle, and is finally attached to the humerus 

 proximal to the radial crest. The recovery is also probably 

 to a great extent assisted by the pressure of air due to the 

 momentum of the bird. During the down stroke the wing 

 is usually fully extended, but in the recovery the wrist and 

 elbow are flexed, the patagium at the same time being 

 contracted by the propatagealis and a system of elastic 

 ligaments in connection with it. The wing is also capable 

 of extensive rotation at the shoulder, whereby the angle 

 made by its surface to the horizon can be adapted with 

 great nicety to the most varying conditions. The tendons 

 of the fore-arm and hand are remarkably long and slender, 

 while all the heavier and more important muscles are con- 

 centrated upon the body or near the shoulder. By this 

 means the wing is rendered light and manageable, and at 

 the same time the centre of gravity of the bird is lowered. 

 Note should be taken of the muscles of the hand, which 

 are quite rudimentary, and of the propatagealis muscles. 

 The latter are represented by two muscular slips that rise 

 together from the dorsal end of the clavicle and are inserted 

 by long tendons into the wrist, extensor metacarpi ulnaris, 

 ,and the surface of the patagium ; the tendon of the anterior 

 of the two muscles consists mainly of elastic tissue. Some- 

 what analogous patagial muscles are found in certain flying 

 mammals. 0. C. 64 Y o. 



Presented l>y St. George Mivart, Esq. 

 Shufeldt, Myology of the Raven (London, 1890), p. 66. 



C. 136. Right wing of a Rook (Trypanocoraxfrugilegus), showing 

 the deep muscles. Attention is drawn to the following : 

 The biceps, a single muscle, rising by two tendinous heads 

 from the coracoid and humerus respectively ; it is inserted 

 on the ulna. The deltoid is double and attached to the 

 outer surface of the humerus as far as the external condyle. 

 The entepicondylo-radiales : two powerful proriators of 

 the fore-arm. The supinator (ectepicondylo-radialis) is 



