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Rh reptiles, unless it be some aquatic mosasaurs, but two small bones remaining, probably the radiale and fourth carpale.



. 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 scapulocoracoid; D, left innominate.

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 earlier to the later. In Pteranodon and its allies of the Upper Cretaceous, the carpus is reduced to three bones: a proximal one, articulating with both radius and ulna, and perhaps to be homologized 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 earlier Rhamphorhynchus (Fig. 142 ), 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 Pterodactylus (Fig. 142 ), 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