Vol. XXXIII 



1915 



Johnson, A Four-winged Wild Duck. 473 



forearm forms an angle of about forty degrees with the plane of 

 motion of the primary forearm upon the upperarm, and evidently 

 could offer no hindrance to the movements of the large wing in 

 flight. 



Distally, the forearm bone articulates with two small bony ele- 

 ments which from their position would seem to represent respec- 

 tively the radial (Rad. carp.) and ulnar (Ul. carp.) carpal bones of 

 the normal wing. 



The carpal region of the right side possesses no separate radial 

 element, but such a bone is possibly represented by a knob-like 

 process on the metacarpal element, which forms the articulation 

 with the radius. 



The metacarpal skeleton consists of a single elongate, cylindric 

 bone, somewhat enlarged at its proximal end. It is approximately 

 two-thirds the length of the forearm bone. Articulating with the 

 metacarpal bone and terminating the series is a single relatively 

 short phalanx. 



On the right side (Fig. 3) there is likewise but a single phalangeal 

 element; it is slightly longer than the left and bent medially at 

 right angles to the metacarpal element with which it is immovably 

 anchylosed. 



It will be seen in the figures that a different degree of flexion exists 

 at the two carpal joints. While the joint surfaces here permit of 

 motion, it is clear from the restrictions of the fascia about these 

 joints, as well as from the inadequate muscle supply later described, 

 that movement must necessarily have been very limited. 



Muscles and nerves. Like the skeleton, the muscles of the two 

 accessory wings present similar conditions from the elbow distally, 

 but in the upperarm the left side alone possesses muscles and these 

 are only two in number and of rudimentary character. Distad of 

 the carpal region there are no muscles, but a tendon from one of 

 the forearm muscles finds its insertion beyond this region. 



The rudimentary muscles of the left upperarm are innervated 

 by branches from the nerves to the biceps muscle of the primary 

 wing. The nerve connections to the accessory forearm muscles 

 of this side could not be positively made out on account of previous 

 mutilation. The muscles of the corresponding right forearm 

 receive their innervation from the Nervus brachialis longus inferior 



