338 THE CORRESPONDENCE BETWEEN THE [chap. 



is rotated forwards, so that the preaxial side of the first 

 becomes external, and the really corresponding side of the 

 other becomes internal, so it is with the scapula and ilium. 

 Each has undergone a rotation on its own axis, through 

 nearly a quarter of a circle, and in the opposite direction 

 (see Fig. 126, e and f), so that the inner surface of the one 

 comes to correspond with the outer surface of the other, 

 the anterior border of the one with the posterior border of 

 the other. The long axis of each is also differently inclined, 

 the upper end of the scapula leaning backwards, while that 

 of the ilium is inclined forwards, which makes the resem- 

 blance between them seem still more obscure. 



These views are considerably strengthened by a con- 

 sideration of the disposition of the muscles connected with 

 the various bones in question.^ 



The principal difterences between the shoulder and pelvic 

 girdle of the Mammalia are two : — (i) The rudimentary con- 

 dition of the inferior or ventral section of the girdle (the 

 coracoid) in the former, as compared with the vast deve- 

 lopment of the corresponding part of the lower extremity; 

 (2) the free condition of the anterior as compared with the 

 posterior girdle. It is neither attached to the vertebral 

 column above, nor does it (except in the Monotremata) join 

 the opposite part in the middle line below. To compensate 

 for this, a clavicle is superadded to the anterior girdle in 

 many Mammals, for which there is no exact homologue in 

 the lower extremity. 



It has been shown in Chapters XVI. and XIX. that 

 the terminal segments of each limb present a remarkable 

 general correspondence with certain constant differences. 



1 See **0n the Correspondence between the Parts composing the 

 Shoulder and the Pelvic Girdle of the Mammalia" [Journal of Anatomy 

 and Physiology, vol. iv. p. 239, 1870). 



