the" fore-limb. 315 



B. The Fore-Limb. 



The fore-limb of the rabbit corresponds to the upper limb 

 of man, and maybe divided, like this, into arm, forearm, wrist, 

 and hand. The relative positions of these several divisions 

 are considerably altered from the primitive condition, and are 

 best understood by comparing them with the haman arm in 

 the following manner. 



Extend your right arm horizontally outwards from the 

 shoulder, with the palm of the hand vertical and the thumb 

 upwards : there may now be distinguished a ventral or flexor 

 surface ; a dorsal or extensor surface ; a preaxial border, along 

 which are the thumb and the radius ; and a postaxial border, 

 along which are the little finger and the ulna. 



Next bend the elbow at right angles, so that the fingers 

 point forwards, and bring the whole arm down to the side, 

 rotating it through 90°, so that, the preaxial border becomes the 

 outer and the postaxial border the inner one. Now pronate the 

 hand, turning it through 180°, so that the thumb is brought 

 to the inner side, and the palm directed downwards. Place 

 the rabbit's skeleton in front of you, with the vertebral column 

 vertical, the head directed upwards, and the limbs pointing 

 away from you, and the right fore-limb will correspond in 

 position to your own right arm. Note that the preaxial border 

 is on the outer side in the arm, and on the inner side in the 

 hand," while in the forearm the two bones cross each other 

 obliquely. The hand in the rabbit is fixed permanently in the 

 prone position — that is, with the palm turned downwards. 



1. The arm contains only a single bone. 



i. The humerus is an elongated bone, articulating 

 by its enlarged proximal head with the glenoid 

 cavity of the scapula, and at its distal end, by 

 the trochlea, with the bones of the forearm. 



At the proximal end of the bone, in front 

 of the head, is the longitudinal bicipital 

 groove, for the tendon of the biceps muscle : 

 this is bounded on its inner side by the lesser 

 tuberosity ; and on its outer side by the greater 



