146 PROF. G. B. hOWes ANb w. RiDEWOob ON [Mar. G, 



whether this enlargement may or may not represent a coalesced 5th 

 tarsal (as, indeed, Gegenbaur was inclined to believe, pp. 64-65). 

 We have failed to detect any trace of segmentation of the cartilage at 

 this point. In the Hylidce, however, a second ligament is present, 

 which passes (fig. 1 9) from the postaxial wall of the capsule of the 

 tarso-metatarsal joint, upwards and inwards, for attachment to the 

 epiphysial cartilage of the astragalus and calcaneus. This ligament 

 carries at its outer end a wedge-shaped cartilage, and that we at first 

 took to represent the fifth tarsal. Upon reconsideration, however, 

 we are disposed to regard it as an ordinary intra-articular cartilage of 

 none but physiological significance (for further details see p. 168). 

 Reflection upon these facts has led us to the belief that while the 

 ligament which passes between the third tarsal and the head of the 

 5th metatarsal is the degraded representative of the 4th and 5th 

 tarsalia, the cartilaginous nodule occasionally carried by it is 

 exclusively a vestige of the 4th one. Gegenbaur records the 

 presence of this ligament in Rana esculenta, in addition to the other 

 genera named, and we can confirm his statement. In R. tempo- 

 raria, however, we find no trace of it in the adult, and but a feeble 

 one in the larva. This fact, while lending additional support to 

 Gegenbaur's original deduction, shows how completely the vestige 

 is, as it were, disappearing under our eyes. 



d. Tarsalia 2 «wc?3 {Os cuboideum). — We have already stated that 

 three tarsal elements may exist ; on the other hand, the outermost 

 two of these may not unfrequently be replaced in a long bone 

 (cuboideum), represented in its typical condition at '^ " in figs. 17, 

 24, 27, 29, 31, & 33. It will be observed in all these cases 

 that this structure overlies, more or less completely, the metatarsalia 

 of the 2nd and 3rd digits ; comparison of the same with those forms 

 in which the three tarsalia are found {Bombinator or Ahjtes, figs. 8 

 & 10) leaves little doubt but that the bone represents a confluence 

 of the tarsalia of the 2nd and 3rd digits, as asserted by all recent 

 authorities. 



In some cases, however, examination of the adult limb would 

 appear to render this questionable. For example : in Hyla ccerulea 

 (fig. 19), in which two tarsalia are alone present, the larger one 

 is little, if at all, related to the 2nd metatarsal — the head of which 

 is in apposition with the second and smaller element. Com- 

 parison of this tarsus with that possessed of the three tarsalia 

 (figs. 8 & 10) renders it hard, indeed, to say which two elements 

 are represented in the Tree-Frog. Born has already experienced 

 this difficulty in dealing (6, p. 443) with the adults of Phryne 

 vulgaris and Bu/o variabilis, and he admits his inability to settle 

 the question, for want of embryological material. 



On turning to the larva of Hyla (fig. 21), we find that the outer 

 of the two elements has (unlike that of the adult) more than twice 

 the bulk of its fellow, while it agrees in every detail with the cuboi- 

 deum in its most typical form (cf. Xenophrys, fig. 17). Examina- 

 tion of this element side by side with that of the adult limb (fig. 19) 

 shows that its growth is arrested early in development : it shows. 



