OSTEOLOGY 



1 I'O 



on the outer side into a strong flat process, the upper surface 

 of which is slightly grooved for the reception of the tendon 

 of the extensor metacarpi radialis muscle. 



The carpus of recent birds consists only of two separate 

 bones. But in the embryo there are six separate cartilages. 

 The two bones which persist are looked upon by ZEHNTNER 

 as ulnare + intermedium and radiale + centrale. The three 

 distal carpals, according to PAEKER, fuse with their three 

 metacarpals. In the emu, according to PARKER, there are 

 no carpal elements either in the young or adult, in Casuarius 

 galeatux there is a small ulnare. 



Though no bird has more than three more or less com- 



Fir;. 70. RADIUS AND ULNA or Metopidiits (AFTER FORBES). 



plete digits, there is commonly a trace of a fourth meta- 

 carpal, found by ZEHXTXER in the development of the swift, 

 and by STUDER in the development of the penguin. PARKER 

 was convinced of the existence of a prepollex and of inter- 

 calary digits, but WIEDERSHEIM looks with no favour upon 

 this broadening of the hand. 



The metacarpals are free only in Archceopteryx and 

 Gastornis ; in all other birds they are partially fused. The 

 formula for the phalanges in Arcliceopteryx is I. 2, II. 3, 

 III. 4. In some other birds it is I. 1, II. 2, III. 1, with the 

 exception of the ostrich, 1 Numenius, and the embryo duck,' 2 

 where digit III. has a small additional phalanx. In other- 

 birds the formula is I. 2, II. 3, III. 1, and in the apteryx 

 digit II. shows three phalanges in the course of its develop- 



1 PARKER, ' On the Structure and Development of the Wing in the Common 

 Fowl,' Phil. Trans. 1888, p. 385, where previous literature is quoted. 



2 BAUR, Science, vol. v. p. 355. 



