xx.] ANTERIOR AND POSTERIOR EXTREMITY. 365 



In what may be considered the first stage of modification 

 (Figs, c and D), each segment of the limb is simply bent 

 upon the one above it. The proximal segments (humerus 



r 



ir 



FIG. 134. Diagrammatic representation of the positions of the limbs of Mammalia, 

 continued. (E) the anterior extremity with the same flexures as in c, but with the 

 whole limb rotated backwards. The pre-axial side is external. The letters as 

 before. (F) the posterior extremity, with the joints bent, and the whole limb rotated 

 forwards, as in the ordinary position of quadruped Mammals. The post-axial side 

 is external. (G) the humerus in the same position as in E, but the fore-arm rotE.ted 

 as in the ordinary position of quadruped Mammals. Whilst the pre-axial side of 

 the humerus remains external, the post-axial side of the manus is now external. 

 (H) the anterior extremity of a Cetacean (Hyperoodon), dorsal surface, (i) the 

 posterior extremity of a Seal, dorsal surface. 



and femur) remain unchanged in position, the dorsal surface 

 still looking upwards, and the ventral surface downwards ; 



