36 COMPARATIVE ANATOMY 



post-axial. Similarly, in the leg, the tibia is pre-axial, the 

 fibula post-axial. In the wrist we find a proximal row of three 

 bones radiale lying beyond the radius, ulnare lying beyond 

 the ulna, and a median bone, the intermedium, lying between 

 them. The distal row has five bones, and we begin counting 

 from the pre-axial or radiale side. The thumb, therefore, is 



Fig. 5- 



Diagram of the typical fore and hind limbs of a pentadactyle vertebrate. The 

 arrow represents the principal axis of the body, the point directed anteriorly. 

 The limbs are represented as stretched straight out at right angles to the 

 principal axis, palms downwards. Sc, scapula ; //", humerus ; Ra, radius 

 (pre-axial with regard to the secondary axis) ; //, ulna (post-axial) ; r, 

 radiale; , ulnare; z, intermedium; c, centrale ; i, 2, 3, 4, 5, the distal 

 row of five carpals ; /, //, ///, IV^ V, the five digits ; //, ilium ; Fe, Femur ; 

 Ti, Tibia (pre-axial) ; Fb, Fibula (post-axial) ; /, tibiale ; /, fibulare. 



on the pre-axial side. Between the proximal and distal row 

 of carpals a central bone is wedged in. This condition is 

 realised in the hand of the water-tortoise. In the ankle we 

 similarly find a tibiale (pre-axial), a fibulare (post-axial), and 

 between them an intermedium. There is a centrale and 

 a distal row of five bones. This condition is realised in the 



