xx. I ANTERIOR AND POSTERIOR EXTREMITY. 335 



Seals, there is a slight bend at the elbow and the wrist, 

 but little or no rotation of the fore-arm. 



In the hind limb of the Seal (Fig. 1) there is very little 

 flexure at the joints, and the whole limb is turned backwards 

 instead of forwards from the hip, and at the same time 

 rotated on its axis, so that the preaxial border becomes 

 turned downwards. The skeleton of this limb, therefore, 

 and that of the fore limb of the Cetacean, being retained 

 normally in almost exactly similar positions, are well adapted 

 for demonstrating the correspondence between the re- 

 spective bones of which they are composed (see Figs. 

 h and 1). 



The necessity of the modifications in the direction of the 

 axes of the heads of the humerus and femur spoken of pre- 

 viously will easily be understood by a consideration of the 

 relative positions that these bones are adapted to assume. 

 Thus the axis of the head of the humerus in the majority of 

 Mammals is inclined towards the postaxial side of the shaft 

 of the bone, while that of the femur is inclined towards 

 its preaxial side. 



Hitherto nothing has been said about the shoulder and 

 pelvic girdle, because the correspondence of their parts is 

 not so easily explained, nor so generally recognised, as that 

 of the segments of the limb proper. The following view 

 appears to be, of those yet suggested, the most probable. 



It has been already shown (Chapters XIV. and XVII.) 

 that the lateral half of each girdle consists primarily of a 

 bar or rod placed vertically, and divided into an upper and 

 a lower segment, the point of attachment of the limb being 

 close to the junction of these two segments. The upper 

 segment in the fore limb is the scapula, in the hind limb the 

 ilium ; the lower segment in the fore limb is the coracoid, 

 in the hind limb the ischium and pubis. 



