1888.] THE CARPUS AND TARSUS OF THE ANURA. 1/7 



" cuboideum " (2, 3). This compound is interposed between the 

 astragalus and the heads of metatarsals 2 and 3. 



Naviculare (centrale), n', and hallux-tarsal. — The former articu- 

 lates obliquely upon the epiphysial cartilage of the astragalus ; its 

 outer face bears two convexities of nearly equal size, which are 

 separated by a shallow groove. The ventral convexity furnishes 

 the main articulation for the pre-hallux (see woodcut, fig. C). 



The hallux-tarsal (/) is generally, though not invariably, present ; 

 when recognizal)le as a distinct element it assumes the form of a 

 small nodule of cartilage, lying buried up in a confused mass of 

 ligamentous tissue, in the interspace between the postaxial hinder 

 border of the naviculare, the head of the hallux-metatarsal, and the 

 OS cuboideum (cf. p. 14/). In the Bull Frog (R. pipiens) this 

 cartilage ossifies, but we have never observed that to be the case in 

 li. temporaria. 



Pre-hallux (calcar). — Born admits the existence of from 2 to 4 

 pieces in this structure (cf. p. 149), while he records (5, p. 233) the 

 presence of three ^ such in R. arvalis, in contradistinction to Leydig. 



In young Frogs of 20 millim. in length we find four distinct 

 segments of hyaline cartilage. The first or tarsal segment {ph. i.) 

 articulates with the naviculare ; the second or metatarsal one is the 

 largest, and bears a small retral process ; of the third and fourth 

 or phalangeal segments, the latter undergoes degradation and is 

 represented only in ligament in the adult. The three persistent seg- 

 ments ultimately undergo ossification and usually remain distinct. 



IV. Conclusions. 



Fore Foot. 



1. That the pyramidale represents the ulnare, and that there is 

 insufficient evidence upon which to base a final determination of the 

 morphological value of the lunatum. 



2. That the naviculare is a preaxial centrale, and that its connection 

 with the radius is always secondary. 



3. Tiiat a vestigial .oth carpal is present in the adults of the 

 DiscogJossidcB and Pelobatidce. 



4. That that element hitherto regarded as the 5th carpal is a post- 

 axial centrale, and that the living Anura are unique, as an Order, 

 in the invariable possession of two large centralia carpi. 



Hind Foot. 



5. That no traces of a third proximal tarsal element are forthcoming 

 at any stage in development ; and that the morphological value of 

 the astragalus and calcaneus has yet to be settled. 



C. That while the tarsalia of the 4th and 5th digits are often 

 represented in ligament, skeletal vestiges of the fourth one are forth- 

 coming in the Discoglosmlce. 



^ Four actually ; but it will be remembered that he regards our ceutrale 

 (naviculare) as the pre-ballus tarsal. 



