474 Johnson, A Four-winged Wild Duck. LOct" 



(Fig. 3, N. br. 1. inf.). A single nerve enters the fleshy part of the 

 forearm at its base, on the under side, and distributes to the various 

 muscles. This nerve is formed by the union of two branches from 

 the N. brachialis longus inferior, one of which accompanies the 

 radial branch of the last named through the slit-like passage formed 

 , between the upperarm bones. No branch from the Nervus radialis 

 was found to pass to the muscles of the supernumerary wing. 



The ulnar branch of the N. brachialis longus inferior, instead of 

 crossing the hollow of the elbow as in normal conditions, reaches 

 its destination by passing around over the convex surface of the 

 anchylosed elbow joint of the accessory wing. 



With regard to symmetry, the arrangement of the muscles and 

 nerves seems to indicate that the primary and accessory wings on 

 each side are not related to each other as right and left, that is, as 

 halves of the undivided wing; but that the smaller wing represents 

 an imperfect copy of the larger. 



On the left side two slender but well defined muscles are connected 

 with the upperarm bone of the supernumerary wing. Both arise 

 as offshoots from the biceps muscle of the primary wing; one from 

 the posterior edge of the tendon of origin of the short head, near 

 its attachment to the head of the humerus; the other from the 

 ventral surface of the belly of the muscle at its proximal end. The 

 fleshy part of the latter of these two muscles extends distally beyond 

 the former, reaching nearly to the elbow joint. Here both insert 

 by closely associated tendon slips, in the angle between the distal, 

 bony process of the accessory humeral element and the correspond- 

 ing forearm bone. 



On the anterior face of the forearm bone lies a relatively large, 

 dorso-ventrally flattened muscle (Fig. 4, 1) which arises by two 

 short heads; one from the area of anchylosis between the forearm 

 and the corresponding upperarm bones, on the outer anterior surface; 

 the other from the anterior surface of the last named bone, adjacent 

 to the anchylosis. The innervating branch from the N. brachialis 

 longus inferior enters between the two heads. The muscle inserts 

 for the greater part of its length on the forearm bone, extending 

 distally as far as the last quarter of the shaft. In position, form 

 and insertion, and in a general way in its origin, this muscle corre- 

 sponds to the M. pronator brevis of normal wings. 



