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



II. GENERAL PART. 



Hind Foot. 



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

 1st, 2iic!, 3rd, 4th, and 5th digits bear, in most genera (c/. 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. 



1). 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. ^Yhen of unequal length, the pre- 

 axial bone, or astragalus, is the shorter. 



Wiedersheim has shown \ in Bana 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 liaAe become greatly elon- 

 gated subsequent to complete fusion (Plate VIII. fig. 12), in a manner 

 strikingly suggestive of the tibia and tibula. 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. 



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

 Salamandrella, Ciyptobranchus) 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 Cryptobranclius, 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 

 dorsalem tarsi reyionem emicandi, quo territorio semel potita, illico 

 in duas, pauUo post in qviatuor 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 veatro-dorsally, however, it diifers 

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

 ■with the arteria brachialis of the fore limb of that animal (c/". 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 loot in the Frog itself; if 



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

 p. 86. 



2 "Die altesten Fornien des Carpus und Tarsus d. beutigen Ampliibien," 

 Morph. Jahrb. vol. ii. (1876), pp. 421-4o5. 



^ Cryptobranclius Japouicus, Schediasma anatomieum. Vindobonae, 1865, 

 p. 113. 



