ANTERIOR EXTREMITY OF VERTEBRATA. 



481 



lu tlie Amphibia the two upper portions are greatly developedj 

 but, except that the radius and ulna are fused in the Anura, they 

 present no such striking differences as those which are seen in the 

 carpus. 



.Some of the primitive carpalia disappear in the distal row; with 

 this is generally correlated a shortening of the fingers, which are 

 commonly limited to four ; or, again, two or three carpalia may be 

 fused together (Frogs, etc.). Concrescence may likewise be seen 

 to affect the proximal series of carpalia. 



In the Reptilia, the various portions of the skeleton of the arm 

 are least altered in the Chelonii, which have not only nine carpal 

 bones, but all five fingers. In the Saurii two of the three carpalia 

 of the first row are fused together ; those of the second row are also 

 greatly modified, and are reduced in number when any of the fingers 

 disappear. The carpus is still more altered in the Crocodilini. The 

 radiale has become much larger than the ulnare, and the second row 

 of carpalia is merely represented by a few elements, which are 

 always partly cartilaginous. The two ulnar fingers are conse- 



Fig. 266. Skeleton of the arm of Ciconia alba. /(.Humerus. « Ulna, r Eadins. 

 c c' Carpus, m Metacarpus, p p' p" Phalauges of the first three fingers. 



quently shortened in comparison with the three radial ones. In the 

 limbs of the snake-like Saurii there are all stages of reduction. 

 The Ophidii are distinguished by the complete absence of these 

 parts. 



In birds, where the whole of the fore-limb is converted into an 

 orsfan of fliofht, the reduction of the manus is still more marked. 

 Two bones only (Fig. 266, cc') are well developed in the carpus, 

 while a piece of cartilage, which corresponds to the second row in 

 the carpus, soon fuses with the base of the metacarpus. Three 

 fingers are always more or less developed in the manus ; in the 

 Saururee these were permanently separate, but in the Ratitaa and 

 Carinatae the metacarpals (m) of the second and third, and generally 

 also that of the first, are fused into one piece of bone. On the 

 third finger there is a rudiment of a fourth one. 



As compared with the Saurii, the number of phalanges is 

 reduced in Birds. In the Saurii, starting from the first finger of 

 the radial side, which has two phalanges, we find one more in each 

 finger as far as the fourth, which has five ; but the fifth finger has 

 not so many. In the Crocodilini this increase stops at the third; 

 in most Birds the second finger has only two phalanges (p'), the 



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