DEGEXERATIOX IX I.IMIiS OF LIZARDS. 



271 



In the fore-Unib (Fig. 2) only two digits are present. With- 

 out intermediate stages for comparison, it is impossible to be 

 certain which of the normal five digits these represent. From 

 their general relationships, however, they appear to be the second 

 and third of the series, and as such they are tentatively regarded. 

 The number of phalanges is reduced either to one or two on the 

 second digit, and to three on the third digit. In the carpus the 

 radiale and ulnare are distinct bones and the distal row is reduced 

 to three. These may possibly represent the carpalia of digits 2, 

 3 and 4, though it is more likely from comparison with correspond- 

 ing stages in the hind-limb that the outer, post-axial represents 

 the reduced fourth metacarpal. 



^H 



j7Wi 



Fig. 2. — Fore-limbs of Cliatnafxaura avguina. 

 Jtinn. humerus, /. radius, v. ulna, II and III, digits, IV metacarpus of 



fourth digit. 



The hind-limb presents more variability in the degree of 

 I'eduction (Fig. 3). The third digit may have two or three 

 phalanges, while the second maj- have one or two; or, in the 

 latter, they may be altogether wanting, and only a vestige of the 

 metatarsus appear, as shown in Fig. 3d. The fourth digit is 

 wholly wanting, as in the fore-limb, but may be represented by a 

 vestigial metatarsus. In the tarsus a single proximal bone occurs, 

 Mhich probably represents the fused tibiale and fibulare, and in 

 the distal row either one or two separate elements are present. 

 Where two occur, as in Fig 3a, they are the tarsalia of the third 

 and fourth digits, and where only one it may represent the fusion 

 of these two, as in Fig. 3b, or it may be median and represent 



