420 



CHORD ATA. 



Fig. 301. — Diagram of 



THE PeNTADACTYLE 



Limb. 

 proximal extremity 



> 

 X 



The proximal carpal bones are the radiale, intermedium 

 and ulnare, together with the centrale (which in some cases 



is paired), whereas the proxi- 

 mal tarsals are tibiale, inter- 

 medium and fibulare, and also 

 a centrale. In each limb there 

 follow five distal carpalia and 

 tarsalia, each of which bears 

 a metacarpal or metatarsal, 

 followed by the phalanges of 

 the fingers or toes. The primi- 

 tive position of the limbs is 

 not retained, but they become 

 altered. Firstly, they are bent 

 into a Z-shape by a bend 

 downwards between the proxi- 

 mal bones and the distal and 

 a bend upwards between the 

 latter and the carpals or tarsals. 

 The limbs still protrude out- 

 w^ards at right angles to the 

 body, a condition still pre- 

 served in many reptiles with 

 shuffling gait. Secondly, the 

 upper joint (knee or elbow) 

 becomes deflected 

 inwards towards 

 the body, the knee 

 forivards and the 

 elbow backwards^ 

 bringing the post- 

 axial bones to the 

 outside. The feet 

 are at the same time, 

 in each case, twisted 

 forwards through 90° 

 so as to face forwards. 

 In the hind limb the 

 foot and the upper 

 part of the limb are 

 therefore both bent 



CARPALS o'TARSAl.S; 



O'lSTAL EXTREMITY 



