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Show 1888.] THE CARPUS AND TARSUS OF THE ANURA. 149 spurisque unguis." It has been likened by some anatomists to a single element in the tarsus (ex. entocuneiform, Owen, 31, p. 184) ; it is, however, unnecessary to recapitulate these comparisons in detail. All recent writers are agreed as to the variable nature of the pre-hallux, but the range of this has not yet been fully recorded. As will be seen from an examination of our figures, it is very inconstant in size, shape, and detailed characters. For example : in the adult Xenophrys (fig. 17), it consists of a single elongated cartilage which ossifies very late in life, whereas in Hyla (fig. 19) it attains a much greater development, and is segmented into four pieces. Disparity in size is by no means confined to members of different families, for in Pelobates-the type of the family to which Xenophrys belongs- the calcar, while consisting of a single piece, attains enormous proportions and ossifies very early '. In this burrowing genus the calcar supports the well-known horny blade, by means of which the animal is enabled to shovel up the earth. This being so, its early ossification is distinctly associated with the functional requirements of the case. Born at first ascribed (3, p. 448) four segments to this structure in Rana, Bufo, and others. In his later researches, however, he records considerable variation in the same, stating (6, p. 61), "wechselt doch die Stiickzahl v. Rana esculeuta, zwischen zwei und vier, bei Bufo variabilis, zwischen drei und frinf." Our figs. 19 & 19 a agree very well with his description, while they represent the maximum segmentation into lineally disposed elements observed in any specimen. We have already shown reason for regarding Born's basal pre-hallux segment as the centrale (navicu-clare), whence it follows that in no known Anuran does the calcar, as defined by us, ever consist of more than four true segments. This maximum number is reached in Bufo2 (?), Hyla, Hylarana, Leptodactylus, Nototrema, and Rana-representatives, that is to say, of four distinct families. Incident upon the foregoing there arises the question as to whether the unsegmented condition of the pre-hallux is the more primitive one, or vice versa. If the latter be the case, traces of segmentation ought to be forthcoming in the larva) of those forms possessed of the single piece. Born accords to Rana esculenta a maximum of three pieces. In old Tadpoles of R. temporaria, however, we have detected the presence of four distinct segments of hyaline cartilage: the terminal one of these early degenerates and becomes eventually fibrous, and not until then can that fusion of the parts which Born describes 3 take place. The facts recorded by this author alone for Hyla and Bufo (Phryne) (6, pi. 1. figs. 2 & 3) are, in themselves, sufficient to show that the lineally segmented condition is most probably the primitive one. W e are doubtful as to how far the one or two pieces, met with in 1 Born makes the assertion (6, p. 59) that it here bears originally two phalanges: this we cannot confirm. 2 Born (6, p. 61). W e have not observed it. 3 p. 56. W e have not observed this. |