114 GENERAL ORNITHOLOGY. 



compound bone ; for, besides including one or more carpal bones in itself, as already shown, it 

 consists of three metacarpal bones fused in one, corresponding to the three fingers or digits 

 which nearly all birds possess. In feet, it is three metacarpals in one, plus certain carpals ; its 

 full name would therefore be carpo- metacarpus. Much the greater part of this composite bone 

 corresponds to a bird's middle linger ; a small, short part, only at the base and on the radial 

 side, corresponds to the outer finger, as seen in the figure above the bone marked d2 ; while 

 that part corresponding to the inner finger is slender, nearly as long as the rest of the bone, 

 and often fused therewith only at its two ends, leaving between itself and the main metacarpal 

 an open space, as seen opposite the letters nic in the figure. The metacarpus thus compounded 

 articulates at the wrist with both the free carpals ; it bears the digits, almost invariably three in 

 number, with which the wing is finished off; they are marked d2, d3, rf4 in the figure. They 

 are the radial, median, and ulnar digits. The median digit, d 3, extending from £" to D in the 

 figure, is much the largest of the three, and forms the main continuation of the hand; it ordi- 

 narily consists of two jointed phalanges, or bones placed one after the other, but may have a 

 third ^/taZana; ; the first or proximal phalanx is much larger than the other one or two. The 

 inner or ulnar digit, d 4, is borne upon the distal end of the metacarpal bone, alongside the first 

 phalanx of the middle digit j it ordinarily consists of a single small phalanx, but sometimes 

 there is another (the Archccopteryx had four); it enjoys little if any freedom of motion, and 

 occasionally fuses with the first phalanx of the middle finger. The outer or radial digit, d 2, 

 is borne upon the projection near the base of the metacarpus, alongside which it lies, away 

 from the other two fingers ; it ordinarily consists of two phalanges, of which the terminal one 

 is small, and often wanting ; it enjoys considerable motion, being quite freely articulated with 

 the metacarpus, except in Penguins. No bird has, and none is known to have had, more than 

 these three digits; and in the Cassowary, Emeu, and Kiwi there is only one, the inner and 

 outer being lost or reduced to mere traces. Such is the compactness and consolidation of a 

 bird's hand that all the fingers act almost like a single stout tapering digit, only the outer one 

 being capable of much individual action ; though in the Archseopteryx the three metacarpals 

 were free bones like the digits, and the whole hand more like that of a lizard. A bird's three 

 digits are supposed by some to correspond to the thumb and fore and middle fingers of our 

 hands; in this view, the radial digit is ca.\\ed pollex, which means thumb; and the next one, 

 index or forefinger. But I agree with others who consider that birds have lost the first and fifth 

 digits of the ancestral five-fingered, consequently the three they retain correspond to our fore, 

 middle, and ring fingers, or our 2d, 3d, and 4th digits, and so I have marked them d2, dS, dA, 

 in the figure. 



The resemblance of a bird's digits to those of a lizard or mammal is increased by the claws 

 (Lat. ungues) which some birds possess. The Archceopteryx liad claws upon all three of its 

 finger-tips. In recent birds, claws are found on the ends of the radial and middle fingers, es- 

 pecially the former; and in some embryos, as of the Ostrich, there is said to be a rudimentary 

 claw on the ulnar digit. The adult Ostriches of the genera Struthio and Bhea have claws on 

 the radial and middle digits, and so do some Anatidce, and various Birds of Prey, the Cassowary, 

 Emeu, and Kiwi have a claw on the middle digit ; one on the radial digit is well shown by the 

 Turkey-buzzard and other Cathartidce, various Anserine and Gallinaceous birds, some Birds of 

 Prey ; and such a claw has occasionally been found on an oscine bird. The occurrence of claws 

 is more or less irregular, and probably more frequent than is yet known. 



The Mechanism of these Bones is admirable. The shoulder-joint is free, much like our 

 own, permitting the humerus to swing all about; though the principal motions are to and from 

 the side of the body (adduction and abduction), and up and down in a vertical plane. The 

 elbow -joint is a very strict hinge, permitting motion in one plane, nearly that of the wing itself. 

 The finger-bones have little individual motion, as we have already seen. The construction of 



