THE LIMBS 



177 



reptiles, unless it be some aquatic mosasaurs, but two small bones re- 

 maining, probably the radiale and fourth carpale. 



The most remarkable modifications of the carpus are those of the 

 volant Pterosauria (Fig. 142). The earliest stages we do not know, 

 though certain progressive modifications are observable from the 

 earher to the later. In Pteranodon and its allies of the Upper Cre- 

 taceous, the carpus is reduced to three bones: a proximal one, articu- 

 lating with both radius and ulna, and perhaps to be homologized 



Fig. 143. Squamata, Rhiptoglossa. Limbs, etc., of Chameleon, much enlarged. A, right 

 hand, dorsal; B, right hind foot, dorsal, with tibia, fibula, and tarsus; C, right scapulo- 

 coracoid; D, left innominate. 



with all the bones of the proximal row except the pisiform; a distal 

 one, composed either of the greatly enlarged fourth carpale, or a 

 fusion of two or three, probably the former; a third carpale, on the 

 radial side, articulating chiefly with the [distal] carpale, may be 

 either the first carpale, the centrale, or possibly neither. In the 

 earher Rhamphorhynckus (Fig. 142 b), there are two distal carpals, 

 the first articulating with the first three metacarpals, the second with 

 the fourth or wing metacarpal. This is also the structure in Ptero- 

 dactylus (Fig. 142 a), except that in some forms there are five bones, 

 two in the proximal, two in the distal row, and the usual lateral one 

 supporting the pteroid. This great consolidation of the carpus in. 



