SKELETOlSr 



859 



said (pages 439, 440) y (2) tli^ forearm, consisting; of the Radius, 

 before mentioned (page 762) and Ulna ; and (3) the Carpus 

 (page 77, 78), Metacarpus (page 547) and Digits, which last 

 three form the hand. According to Prof. Gegenbaur, the original 

 arrangement of the wrist-bones consisted of (a) three proximal ele- 

 ments — the carpale ulnare, c. intermedium, and c. radiale ; (b) one 

 median element ; and (c) five distal carjjals, each of which carried a 

 metacarpal with a digit. In Birds these elements are much reduced 

 b}' fusion and suppression, so that theie are now only two free 

 carpals — one, generally termed the " radial," but resulting from the 

 fusion of the c. radiale with the 

 c. intermedium, and articulating with 

 the distal end of both radius and 

 ulna ; and the other, the so-called 

 " ulnar," which is really the centrcde 

 and idnare combined, and articu- 

 lates with a small portion of the 



Common Fowl, Embryo and Adult. 

 c.cl. diiital carpals 1-3; H. Humerus; M. 



ulna only. The distal carpals are ^j j/^ 

 now reduced to three, the fourth 

 and fifth being lost. They fuse in 

 the embryo with the proximal end 

 of the three first metacarpals, and 

 all trace of their originally separate 

 existence disappears when the hand 

 is completely ossified. 



The greatest reduction of the 



carpal bones prevails in the KatitX. Metacarpals 1-4; R. Radius ; r. radial carpal; 



Setting aside the Dinornithes, of ^- uina ;«. ulnar carpal, 

 which only remnants of a humerus are known, Casuarius galeafus has 

 only one separate carpal, which is probably the c. ulnare, while in 

 Apteryx oiveni and in Dromaius even this is suppressed. 



The Metacarpus is composed of three bones, the first, second 

 and third metacarpals, while trace of a fourth has been observed 

 in embryos. The first of these is the shortest, and bears the 

 POLLEX (page 737). In most Birds it fuses throughout its length 

 with the intier margin of the second, which, as well as the third, 

 is much longer. The ends of these fuse, the proximal first and 

 the distal later, leaving as a rule a space between the shafts. The 

 second is by far the strongest, generally straight, and bears the 

 INDEX (page 459), while the third is outwardly bowed and much 

 more slender, being in a degenerate condition.^ In embryos it 

 sometimes still shews two phalanges, but these are soon reduced 

 to one, which, resting closely against the proximal phalanx of the 

 second digit, occasionally fuses with it. Curiously enough this 



^ Of all Birds Arclixopteryx alone is known to have had 3 free metacarpals, 

 and 3 free digits, with 2, 3 and 4 phalanges respectively. 



