OSSEOUS SYSTEM OF AVES. 73 



ulnar side, rather concave from the anconal to the pahnar side, 

 and this chiefly at .the ulnar part of the trochlea. On the 

 radial side of this trochlea, supported by a tuberosity, is the small 

 surface for the radius. The interosseous space, OAving to the 

 greater bend of the ulna, is widest in GallincB ; it is narrower and 

 chiefly seen at the proximal half of the antibrachium in most 

 other birds. The ulnar trochlea articulates mth the two free 

 carpal bones, one — the ' scapho-lunar ' — being wedged into the 

 radial part, the other — ^ cuneiforme ' — into the ulnar part, leaving 

 a small intermediate tract for the ' magnum ' which is confluent 

 ^vith the base of the mid-metacarpal. 



In the young Ostrich the metacarpus consists of three bones. 

 The one on the radial side answers to that of the index-finger ; it 

 is very short, and supports a digit of two phalanges, the second 

 phalanx being armed with a long curved and pointed claw. The 

 second metacarpal is the longest and largest, its base being in- 

 creased by the confluence therewith of the * magnum,' which 

 presents a trochlear surface to the two proximal carpals and to 

 the part of the ulnar joint not occupied by them. The third 

 metacarpal, answering to that of the digitus annularis, is bent, its 

 extremity resting against that of the large and straight middle 

 metacarpal, mth which it subsequently becomes anchylosed. 

 The middle digit consists of three phalanges ; the outer one of 

 two phalanges. In aU birds the three metacarpals, here seen to be 

 distinct, coalesce with one another and form a single bone, having 

 an interesting analogy to the metatarsus, wiiich Like^^^se consists 

 in all birds of a coalescence of the three bones supporting the 

 corresponding toes, namely, those answering to the second, third, 

 and fourth in the pentadactyle foot. 



The bones of the hand are developed in length, but contracted 

 in breadth. The wedge-like adjustment of the free carpals is 

 such as to restrict the movements of the hand upon the arm to 

 abduction and adduction, or flexion in the ulno-radial plane, 

 requisite for the outspreading and folding up of the wing. The 

 hand of the bird moves thus in a state of pronation, without the 

 power of rotation or of proper flexion or extension, i.e. in the 

 ancono-palmar direction ; so that the wing strikes firmly and vnXh. 

 the full force of the depressor muscles upon the air. 



The following state of anchylosis commonly exists in the meta- 

 carpus : — The short ' index ' metacarpal coalesces with the base of 

 the * medius ' : the slender ' annularis ' metacarpal anchyloses by 

 its two ends with those of the medius which it equals in length. 

 The ^ index ' supports one phalanx, usually terminating in a point 



