LIMBS 



161 



Fe- 



FL 



Round a centra /e, which may be double, is arranged a series of 

 other elements, of which three are proximal, and a varying number 

 (four to six) distal. The proximal, in correspondence with their 

 relations to the bones of the fore-arm and shank respectively, are 

 spoken of as radiale or tili'tl<', ulnare or fibula re, and intermedium ; 

 while the distal are called carpalia or tarsalia (in the narrower 

 sense). They are counted 

 beginning from the pre- 

 axial (radial or tibial) side 

 of the limb. 



Amphibians. The 

 anterior and posterior 

 extremities of Urodela 

 are formed essentially on 

 the ground-plan described 

 above, but more or fewer 

 of the carpals or tarsals 

 may undergo fusion. In 

 them, as in Anura, there 

 are five digits in the 

 hind-limb, and usually 

 only four in the fore- 

 limb. In the Anura the 

 radius and ulna become 

 united, and a separate 

 intermedium is not re- 

 cognisable; the proximal 

 row of the tarsus, more- 

 over, consists of only two 

 cylindrical bones, one of 

 which (astragalus) corre- Fl(1 

 sponds to a tibiale, and 

 the other (cakaneum) to %, + digits ^/V-.^femur; Fi^, fibula; 



a fibulare (Fig. 124). 



In the distal row of 

 the carpus four separate 

 elements are formed in 



Anura, but this number may become reduced owing to secondary 

 fusion ; in rare cases a fifth carpal may also be present. Tarsalia 

 // and /// are the most constant elements, but even these may 

 undergo fusion, and tarsalia /Fand Fare generally represented 

 by a ligament. 1 



In Anura the metat:\rsals and phalanges, between which the 

 web of the foot is stretched, are, like the proximal tarsals, very 

 long and slender. The femur, as well as the fused bones of the 



1 Very different views are held with regard to the homologies of the 

 individual carpals and tarsals in Amphibians, and the older numbering and 

 nomenclature are therefore provisionally retained here. 



M 



^ 



1-23. HIND LIMB OF A URODKLE (Spderpes 

 fuscus). 



, meta- 



tarsals (7 V) : Ph, phalanges ; T, tibia ; 

 Ta, tarsus, consisting of c, centrale ; f, 

 fibulare ; i, intermedium ; t, tibiale ; and 

 1 5, distal tarsalia. 



