THE FOKE-LIMB 287 



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-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. 



1. The arm contains only a single bone. 



i. The Immerus 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 

 tuberosity, a large roughened projection con- 

 tinued as a ridge down the anterior surface of 

 the bone as far as its middle. 



The trochlea at the distal end of the bone 

 is an oblique pulley-like surface, divided in 

 front by a ridge, and articulating with the 

 radius and ulna to form the elbow-joint. 

 Immediately above the trochlea, in front and 

 behind, are the supra-trochlear fossae, which 

 communicate with each other through the 



