1888.] THE CARPUS AND TARSUS OF THE ANURA. 149 



spuriaque 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 pro- 

 portions 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, Bvfo, and others. In his later researches, however, he 

 records considerable variation in the same, stating (6, p. 61), 

 " wech&elt doch die Stiickzahl v. Rana esculeuta, zwischen zwei 

 und vier, bei Bufo variabilis, zwischen drei und fiinf." 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 Bom'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 Bufo' (?), Hyla, Hxjlarana, 

 Leptodactyhis, 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 larvae of those forms 

 possessed of the single piece. Born accords to Rana esculenta a 

 maximum of three pieces. In old Tadpoles of R. temporai-ia, 

 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 " take place. The facts recorded by this 

 author alone for Hyla and Bufo {Pliryne) (6, pi. 1. figs. 2 & 3) 

 are, in themselves, sufficient to show that the lineally segmented 

 condition is most probably the primitive one. 



We are doubtful as to how far the one or two pieces, met with in 



' Born makes the assertion (6, p. 59) that it here bears originally two pha- 

 langes: this we cannot confirm. 



- Born (G, p. 01). We have not observed it. 

 ^ p. 56. We have not observed this. 



