THE FORE-LIMB 295 



ii. The clavicle is a slender curved membrane-bone, 

 rather less than an inch in length, and formed 

 by ossification in the ligament running from 

 the scapula to the sternum. 



Small cartilaginous nodules occur, one at 

 the outer and two at the inner end of the 

 clavicle. 



B. The Fore-Limb. 



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

 man, and may be 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 human arm in 

 the following manner. 



Extend the 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 nearly at right angles, so that the 

 fingers point horizontally forwards, and bring the whole arm 

 down to the side, rotating it through 90°, so that the preaxial 

 border becomes external and the postaxial border internal. 

 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-hmb 

 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. 



1. The arm contains only a single bone. 



i. The humerus is an elongated bone, articulating 

 by its enlarged proximal head with the glenoid 



