OSSEOUS SYSTEM. 79 



mostly directly forward, and forms the metacarpal bone of the middle 

 finger; the smaller bone directed backward supports on its apex 

 the little finger, while at the base and from the radial side of the 

 middle metacarpal, a strong process is met with, which supports the 

 thumb, and forms the rudiment also of its carpal bone. The thumb 

 itself mostly consists of an elongated phalanx of considerable size, 

 which supports the spurious alule or winglet; not urifrequently, 

 however, as in the Ostrich, the Duck, and Swift, it supports a ter- 

 minal phalanx provided with a horny covering. The thumb is 

 wanting in the Penguin. The middle finger is the longest, and con- 

 sists for the most part of two, more rarely, as in many Palmi- 

 pedes, the Ostrich, and Emeu, of three joints ; in the last-named 

 bird a strong nail is met with upon the distal phalanx ; the first 

 phalanx is a tolerably broad bone. The little finger has in all cases 

 probably only one phalanx. In this manner the hand of the Bird, 

 without overstraining the homologies of its constituent parts, may 

 be readily compared with that of the Mammalia. In some Birds; 

 which are possessed of great powers, of flight, e. g. Cypselus and the 

 Humming-bird, the portion which forms the hand is the largest in the 

 whole skeleton of the arm. In the Penguin, also, the case is very 

 similar, only the bones here are all situated in a rudimentary wing 

 which has been converted into a paddle, and are therefore completely 

 flattened, reminding us of the like condition of the anterior extremi- 

 ties in the Dolphin. In the Apteryx the hand is still more simple 

 than in cases where it exhibits only a single three-jointed digit, for 

 there a solitary phalanx, provided with a claw, is supported by tne 

 small metacarpal bone, and forms what is called the spur of the wing. 

 The horny spur in Palamedea, Parra, Charadrius spinosus, and other 

 birds, is firmly implanted upon a long process of the rudimentary 

 metacarpal bone of the thumb. 



As regards the movement of the anterior extremities in the bird, 

 the arm is found placed in the position of pronation, and the hand 

 is not capable of true flexion and extension, but merely of abduction 

 and adduction, so that the rowing movement of the wings through 

 the air in flight may be performed in the most efficient manner. 

 The curves also of the articulating surface of the distal end of the 

 humerus, upon which the radius and ulna move, are so differently 

 arranged, that the two bones of the fore-arm, if flexed and extended 

 upon each other in the longitudinal direction, would be inevitably 

 dislocated. The radius acts in flexion by being pushed forward 

 upon the corresponding small bone of the carpus, by which move- 



