162 PROF. G. B. HOWES AND W. RIDEWOOD ON [Mar, R, 



■with the absence of that definiteness of articulation between them, 

 met with in nearly all other Anura. Pipa stands alone, as before 

 stated (p. 161), with respect to the fusion of the postaxial carpal 

 elements ; the resulting bone {pic) certainly includes the postaxial 

 centrale and the ulnare, but we are unable to say whether our 5th 

 carpale is or is not embodied. We incline to the belief that it is 

 not. Comparison of the young and adult feet (fig. 2, h) shows that 

 this compound undergoes a shortening up during development. Its 

 postaxial lobe (* of fig. 1 ) is of purely physiological significance and 

 late in origin. 



Ventrally to the lunatum there is present a large lenticular bone 

 (indicated by a dotted line in fig. 1). Baur has shown that, in the 

 Urodele hind foot, an element of the tarsus ^ may be thus visible 

 only on one surface, and hence we have studied with care the rela- 

 tionships of this element. It lies wholly out of the plane of the true 

 carpal elements and is surrounded by tendinous tissue, while it is 

 totalfv absent in the young specimen at our disposal. We regard 

 this combination of characters as proof that it is a sesamoid. 



The element marked po. i. is somewhat interesting. In the adult 

 it is lenticular, and in articulation with both the naviculare (w) and 

 the head of the 2nd metacarpal (2'). It might therefore appear, 

 from its relationships, to be the carpal of the second digit. In the 

 young specimen, however, it is exceedingly small (fig. 2) and wholly 

 destitute of connection with the metacarpal ; on comparison with 

 Xenopus (fig. 4), in which the carpal of the 2nd digit is distinct, it 

 is clear that it can only represent the cajpal of the poUex \ carpal 2 

 having, in all probability, become confluent with the naviculare. 

 Examination of the young specimen (fig. 2) renders this doubtful, 

 for the head of the 2nd metacarpal bears an enlargement, such as 

 might conceivably have resulted from a confluence with its carpal. 

 Upon this point we have been unable to obtain decisive evidence. 



Hind Foot. 



The most complete observations hitherto made upon the tarsus of 

 this genus are those of Mayer (28). The hind foot is, like its fellow 

 in front, very anomalous. The astragalus and calcaneus are widely 

 separated and fused at their ends, leaving an elliptical hole in the 

 middle ; the compound thus arising is only twice as long as broad. 

 The outer edges of the two bones — i. e. the preaxial border of the 

 astragalus and the postaxial one of the calcaneus — are ridged in such 

 a manner that each bone is T-shaped in transverse section. 



The 4th and 5th metatarsals articulate directly upon the epiphy- 

 sial end of the calcaneus, while the remaining three are as it were 

 shut out from that of the astragalus by thin lamellae of bone. These 

 lamellse are seen to be continuations of two out of three bones which 

 lie on the ventral side of the tarso-metatarsal joint, and would appear 



1 Centrale 2 oi Necturus (1, p. 20). 



'^ The adult limbs at our disposal were skinned befoi-e they reached us, hence 

 we are unable tu make any definite statements concerning the poUex itself. 



