1888.] THE CARPUS AND TARSUS OF THE ANURA. 175 



most 18 to 20 mm. in length, it flanked from one-third to three- 

 fourths of the pieaxial border of the liinatum. In these, as in the 

 adult (fig, 2), it is four-cornered as seen from the dorsal aspect ; in 

 old Frogs it becomes triangular and it may fuse with the lunatum, in 

 the manner already described (p. 172) for Microhijla. 



The lunatum (/.) articulates proximally with the epiphysial 

 border of the radius, preaxially with the naviculare by a concave 

 or flattened surface, and postaxially with the proximal half of the 

 inner border of the ulnare (pyramidale) — between it and the distal 

 half of this boue the foramen intercarpi is enclosed {cf. p. 156). 



The ulnare {pyramidale) (p.) is in articulation proximally 

 witli the ulna and distally with the large capitato-hamatum (3, 4 k) 

 of the distal row ; the hinder half of its preaxial border is free, as 

 above stated. The articulations of tliis element are of a loose order 

 with the exception of that associated with the capitato-hamatum ; 

 this bears antero-ventrally a projecting socket, which is excavated to 

 receive a corresponding and prominent downgrowth of the ulnare. 



Looked at in situ, with the fore foot in the extended position, the 

 lunatum is most dorsally extended, and the ulnare most ventrally 

 so. Examination of the parts thus shows that, while the rotation 

 of the fore foot upon the radius and ulna has aifected the articulation 

 between these bones and the proximal carpals as a series, it has also 

 brought about a less conspicuous rotation of the proximal upon the 

 distal carpal elements. 



Capitato-hamatum (3 4 k). — It is needless to recapitulate the 

 grounds upon which we have come to regard this as a compound 

 of the 3rd and 4th carpalia of previous workers with our postaxial 

 centrale. Postaxially it sends up a lobe which embraces the free 

 border of the ulnare, much in the manner of the secondary relation- 

 ship assumed between the naviculare and lunatum. Proximo-inter- 

 ually it articulates with the naviculare, lunatum, and ulnare, distally 

 so with the metacarpals 3, 4, and 5, by special condyles. This com- 

 pound transmits ventrally, in the adult, the lateral ramus of the 

 ulnar nerve ; the foramen through which that passes is, in young 

 animals, represented by an open groove {cf. p. 160). 



Carpal of 2nd digit. — This element (^) varies considerably in 

 shape, being sometimes rectangular, at others convex on all sides 

 and ajiproximately spherical. 



Carpal ofthepollexC). — This is more fully represented than might 

 be imagined, on a knowledge of the great reduction of the pollex 

 itself. It is strongly convex externally, and concave internally, for 

 articulation upon the carpal of the second digit and the naviculare 

 respectively. 



Pollex. — This is invariably in a vestigial condition, consisting in the 

 adult (see woodcut, fig. B) of a single piece, excluding its carpal, with 

 which it is in definite articulation by a facet. Applying arguments 

 previously adduced (p. 149), we regard this structure as representative 

 of the entire first digit, rather than of its metacarpal alone as is more 

 generally and empirically asserted. 



Metacarpals. — In the male the metacarpal of the second digit 



13* 



