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Show 148 PROF. G. B. HOWES AND W. RIDEWOOD ON [Mar. 6, between the first tarsal and the astragalus, being in fact absolutely central and in a position which cannot, by any stretch of imagination, be said to be " in einer Reihe mit den Tarsalknorpeln." It would be more correct to say that the 1st metatarsal, 1st tarsal, and naviculare are here disposed lineally. Examination of the Plates will show that the relative size of the naviculare is in no way proportionate to that of the pre-hallux, as might be expected were Born's hypothesis tenable (cf. figs. 3, 10, 12, & 17) ; it is rather the reverse. Choice appears to lie between two alternatives : the naviculare has either grown in and displaced the hallux tarsal proximally (as the Biscoglossidce would suggest, figs. 8 & 10, in which case the condition of the latter would, in this family, be secondary) or it has undergone a reduction proportionate with an increase in size of the same. Recent observers are agreed as to the lowly position of the Discoglossidce1, and it therefore becomes a question of first importance as to how far the arrangement just described in them is primary. In the youngest DiscoglossidoB examined by us (cf. p. 164), no appreciable difference could be detected in the relative proportions of the two elements under consideration as compared with the adult; we have here, then, strong reason for regarding the condition exemplified in them as really primary. The matter, however, presses still more closely. Examination of those forms in which the pre-hallux is regularly segmented (fig. 19), shows that that segment which Born regards as its metatarsal (ph. i.) is generally disposed in a line with the naviculare, n' (cf. figs. 13 & 19). In Pelodytes, however (fig. 13), and less conspicuously in Alytes (fig. 10) and Hyla, the first-named element is intimately connected with the adjacent hallux-tarsal (1) by means of a well-defined ligament, which runs distally to the naviculare. Comparison of this ligament with that previously referred to as the representative of the 4th and 5th tarsalia, leaves little room for doubting, if argument from analogy is worth anything, that Born's metatarsal of the pre-hallux is, in reality, its tarsal. If this be admitted, there can no longer be any doubt of the homology of Ecker's naviculare (..') with the os centrale tarsi. This determination brings the tarsus of the Anura into closer harmony with that of the other and, especially, the higher Vertebrata than is now generally admitted, while it sets at rest further doubt as to the value of the hallux-tarsal. Finally, Ecker has shown (17, p. 128) that the tendon of the adductor longus digiti primi muscle (m.a.l. of woodcut, fig. C, p. 1/6) is inserted into the naviculare. W e have found this to be invariably the case whether the hallux-tarsal is present or absent. It follows, therefore, that all possible source of confusion between that element and the naviculare is at an end. g. Pre-hallux (Calcar).-The skeleton of the pre-hallux was first figured by Rosenhof (32) ; he described it (Pelobates, p. 84) in the words " tandem etiam in sceleto hoc notari meretur singularis quidam 1 Cf. Cope (12, p. 104) and Boulenger (7, p. 444). |
