144 PROF. G. B. HOWES AND W. RIDEWOOD ON [Mar. 6, 



II. GENERAL PART. 



Hind Foot. 



a. Metatarsals and Phalanges. — Setting the pre-hallux aside, the 

 1st, 2ac!, 3rd, 4th, and 5th digits bear, in most genera {cf. foot- 

 note on p. 178) respectively 2, 2, 3, 4, 3, phalanges, the 4th, or 

 outermost digit but one, being the longest. Pipa is alone excep- 

 tional, for in it the 3rd exceeds the 4th in length. 



b. Astragalus (a.) and Calcaneus (c). — These two elements were 

 already greatly elongated in the youngest specimens in which their 

 presence could be detected. When fully formed, the two bones are 

 generally uniform in length ; they are relatively longest in the Tree- 

 Frogs, shortest in Pelobates. When of unequal length, the pre- 

 axial bone, or astragalus, is the shorter. 



Wiedersheim has shown *, in Rana esculenta, that the arteria 

 interossea perforates the membrane passing between these two bones, 

 dorso-ventrally, to reach the plantar surface of the foot. Pelodytes 

 is alone exceptional, among all the genera which we have examined, 

 in the fact that its astragalus and calcaneus have become greatly elon- 

 gated subsequent to complete fusion (Plate VIII. fig. 1 2), in a manner 

 strikingly suggestive of the tibia and fibula. The above-named 

 artery, however, remains true to its original relationships, a small 

 foramen (/.i'., fig. 12) being left for its transmission. In this, as 

 in all other genera, neither the astragalus nor calcaneus (however 

 much modified) ever undergo any sort of rotation ; they lie side by 

 side, invariably complanate with the tibia and fibula. 



Wiedersheim has shown further" that in the Urodela (Ranodon, 

 Salama7idrella, Cryptobranchus) a blood-vessel perforates the 

 tarsal region apparentl}', at first sight, in the manner of the above- 

 named artery of the Frog. Baur has more recently recorded the 

 same fact for Necturus (1, pi. i. figs. 12 & 17)- Hyrtl, describing 

 the vascular system of Cryptobranchus, says of the crural artery ^ : — 

 "horum ossium biga, cui nulla articulatio intercedit, et quae potius 

 textu fibroso in unum quasi corpus conjungitur, arteriae nostrae 

 commodam praebet occasionem, trajecta syndesmosi intertarsea, ad 

 dorsal em tarsi regionem emicandi, quo territorio semel potita, illico 

 in duas, paullo post in quatuor arterias digitales communes dorsales 

 dilabitur, binorum digitorum interstitiis destinatas." There can be 

 little doubt but that this description applies to the vessel noted by 

 Wiedersheim. In that it passes ventro-dorsaliy, however, it differs 

 in to to from that of the Frog, but in this it agrees just as closely 

 with the arteria brachialis of the fore limb of that animal {cf. p. 156). 

 These facts tend to show that the perforation in question (foramen 

 intertarsi, [auct.]) is probably not homologous with either that of 

 the Urodele hind foot, or that of the fore foot in the Frog itself; if 



^ Anatomie des Frosclies, Ecker and Wiederslieim, Part I [., Brunswick (1881), 

 p. 86. 



2 "Die iiUesten Formen des Carpus und Tarsus d. heutigen Amphibien," 

 Morpb. Jahrb. vol. ii. (1876), pp. 421-435. 



3 Oryptobranclius Japouicus, Schediasma auatomicum. Vindobonae, 1865, 

 p. 113. 



