1888.] THE CARPUS AND TARSUS OF THE ANURA. 159 



(not strictly so in Pelobates), and, at the first glance, we appear to be 

 dealing with the least modified term in the series ; comparison of 

 which with the opposite one (ex. fig. 7) would appear to show that 

 the naviculare was primarily proximal, and that its central position 

 has been assumed as the accompaniment of a reduction of the distal 

 carpals. 



The problem is a very perplexing one. If we admit that the 

 Pelobatoid fore foot is the more primitive, we are forced to the con- 

 clusion that the naviculare belongs to the proximal series ; if we 

 hold the Discoglossid foot to be the more ancestral, we imply that 

 the suppression of the carpalia is not a specialized feature'. In all 

 those cases in which we have obtained sufficiently young larvse, the 

 naviculare is central to begin v\ith and free of the radius, its ascending 

 process being of secondary origin (cf. Discoglossus, larva and adult, 

 figs. 5 & 6). We regard this as conclusive evidence that the navi- 

 culare does not belong morphologically to the proximal series, and 

 hold that the condition of the Pelobatoid limb is a modified one, its 

 naviculare having become displaced, in all likelihood at a very early 

 stage. Nor must the possibility be overlooked that, in those forms 

 in which the naviculare is most completely in articulation with the 

 radius, it may have been to a large degree displaced as the direct 

 result of enlargement of the second metacarpal {Leptodactylus, 

 fig. 25), or carried up with the enlarging pollex {Pelodytes, fig. 11) 

 (c/". p. 171). These are our reasons for regarding the naviculare 

 as a central element, and we propose to term it, in accordance with 

 its position, the preaxial centrale. 



The carpus of the Anura would appear, from the foregoing, to 

 possess two enormous centralia. Duplication or triplication of the 

 centrale is well known in many living Urodeles. Wiedersheim ^ and 

 Baur (l)have paid most attention to this question, and the latter 

 has adduced weighty arguments (I, pp. 68-69) in support of the 

 view that such duplication is purely secondary. The existence of 

 but a solitary centrale in the lowest representatives of the Class 

 {Amblystoma, Baur, p. 40), the great variation in the characters and 

 assumed relationships of the superadded one, the occasional absence 

 of the same {Necturus, Cryptobranchus, and others, pp. 20-29), all 

 point to the conclusion that in this duplication we have to deal with 

 extreme specialization. Turning now to the Anura, we make bold 

 to assert that the hind foot of these animals is, except for its great 

 elongation and changes incident thereon, if anything, less consider- 

 ably modified than the anterior member. What, we ask, could be 

 more extraordinary than the position in whicli the living Xenopiis 

 carries its fore foot 1 and may not the appearance of the second 

 centrale have been originally associated with some such speciali- 

 zation? Taking all facts into consideration, we submit that, as an 



^ It is interesting to obserye here that, whereas in Alytes, Bomhinator, 

 and Biscoglossus, the ossification of the naviculare precedes that of the carpalia, 

 in Xeiiojjkrj/s cp. 4 is the first to ossify. 



^ " Ueber die Vermehrung des Os centrale im Carpus und Tarsus des Axolotls," 

 Morph. Jahrb. vol. vi. (1880) pp. 581-583. For other references see Baur. 



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