CARPUS OF HTMENOCHIBITS BOETTGEEI. 461 



the fact that the ulna is separated from the fifth metacarpal by 

 a single bone, and not two bones as in all other Anurous 

 Amphibians, 



While investigating the byobranchial skeleton of Hymeno- 

 cJiirus, an account of which appears in the pages immediately 

 preceding, it occurred to me that it would be of considerable 

 interest to determine, while the material was still in my hands, 

 whether the carpus of this new genus could throw any light upon 

 the question of the affinities of this form with the two previously 

 known Aglossal Toads. 



An examination of the carpus of HymenocJiirus disclosed the 

 fact that in this genus, as in Pipa, a single bone intervenes 

 between the ulna and the fifth metacarpal. In view of the great 

 variation to which the carpus of the Anura is subject, it is perhaps 

 unwise to attach much importance to this fact ; but it is certainly 

 remarkable that the HymenocJiirus of Africa should thus depart 

 from the generalized type of carpus found in Xenopus (African), 

 and should approach the hitherto unique variety exemplified by 

 the American Pipa. 



The carpus of HymenocMrus (fig. 5, PI. 31) consists of five 

 elements, not including the radial sesamoid {s). This last occurs 

 also in both Fipa and Xenopus. In a joint paper on the Anuran 

 Carpus and Tarsus by Prof. Gr. B. Howes and myself, the ventral 

 surface of the carpus of Xenopus and Pipa is unfortunately 

 figured as the dorsal surface, and the radial sesamoid is stated 

 as occurring ventrally to the lunatum * — mistakes which were 

 pointed out by Jungersen t in 1891. The sesamoid in question 

 is dorsal in position in all three genera, and is lenticular in shape. 

 In HymenocMrus it occupies a more proximal position than in 

 Pipa and Xenopus, and lies over the epiphysis of the radius, — 

 a fact somewhat destructive to the theory put forward by Emery J 

 that this element, in Pipa, is an " intermedium carpi." Since the 

 dorsal radial sesamoid has been shown by Zwick § to occur also 

 in the Frog and Toad, it cannot be regarded as distinctive of the 

 Aglossa. 



The largest bone of the carpus is that which extends from the 

 ulna to the fifth metacarpal {pk). It represents the pyramidale 



* Proc. Zool. Soc. Lond. 1888, pi. vii. figs. 1, 2 & 4, aud p. 162. 



t Ann. Mag. Nat. Hist. [6] viii. pp. 193-206. 



X Ricei'che Lab. Anat. Norm. Roma, iv. 1894, p. 10. 



f Zeitschr. fiir wiss. Zool. Ixiii. 1898, p. 102. 



