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Show 1888.] THE CARPUS AND TARSUS OF THE ANURA. 145 so, the arteria interossea will not help us in the least in estimating the morphological value of the astragalus and calcaneus. Wiedersheim asserts (36, p. 211) that in the astragalus we have " ein vereinigtes Tibiale und Intermedium." Gegenbaur (18) and Born, on the other hand, are inclined to regard the tibiale as its sole representative. Proof of the former statement is not forthcoming; and in spite of the most diligent researching, we have been unable to discover, at any stage, the remotest trace of anything at all comparable to a third proximal tarsal. Future research may, perhaps, demonstrate its existence; but, mindful of the elongation of the earliest rudiments of these elements, we incline to the belief that the missing one (? intermedium) has disappeared beyond all recognition, even during the embryonic period. c. Tarsalia 4 and 5. - I n no Anuran foot hitherto described have there been recognized more than three distal tarsal elements (tarsalia). Examination of the Plates will show that when these remain distinct they are directly associated with the hallux and the two next digits (ex. Plate VII. figs. 8 and 10). The tarsalia of the two outermost digits (4th and 5th) would thus appear to be absent. Gegenbaur first drew attention to the existence, in certain genera, of a ligament (figs. 10, 17, and 19) which passes between the tarsal of the third digit and the head of the fifth metatarsal. He described its relations minutely (18, p. 61), and concluded that " er reprasentirt in ligamen-tosem Zustande Theile, die unter anderen Verhiiltnissen als Knorpel gebildet sind." This structure has been recorded in Hyla, Rhinoderma (Gegenbaur), Pelobates (Gegenbaur, 18 ; Bayer, 2), Discoglossus (Wiedersheim, 36, p. 211), and others, and to the list we are able to add (cf. Part II.). Born says of Phryne (Bufol) vulgaris (3, p. 444) " im Band-polster unter der Basis von Metatarsale IV. traf ich einmal einen deutlichen Rest von Knorpelgewebe, was die Gegenbaur'sche Deut-ung dieses Bandes als Homologon eines Tarsale IV. durchaus bestatigt." W e find that in the adult of Alytes obstetricans this ligament (fig. 10) carries a well-marked nodule of cartilage, which lies between the applied heads of the 4th and 5th metatarsals. That this represents one of the missing tarsals is hardly to be doubted from its relationships, but, from its position, it is difficult to say which. Gegenbaur goes on to assert (p. 61), " wenn man das auf ein blosses Ligament reducirte Tarsusstiick einem der bei den iibrigien Amphibien nachgewiesenen Elementarstiicke vergleichen will, so kann man in ihm nur nach Massgabe der Betheiligung des Metatarsus das Tarsale 4 und 5 erkennen, welches bei den Tritonen schon durch ein einziges Stuck dargestellt war." In Bufo, Hylodes, and Hyla (Plate VIII. fig. 19) the ligament enters into an extensive connection with the head of the fifth metatarsal, like that originally figured by Gegenbaur (18, pi. 4. fig. 13) for the first-named genus. It fuses (fig. 23) with the postaxial articular border of this bone, and the head of the same is seen to be obviously enlarged as the result of its attachment2. It becomes a question of considerable interest, therefore, 1 See Boulenger (7, p. 303). 3 Cf. Xenophrys, Plate VIII. fig. 17. |