4S4 THE RABBIT cHaP. 



moves in one plane — forwards and backwards ; in the 

 rabbit it is a small, curved, rod-like bone, attached by 

 fibrous tissue at one end to the sternum and at the other 

 to the coracoid process of the scapula, there being small 

 cartilages at either end of it. 



Tlic relative positions of the Ijuiies uf the fore-liiub arc at first iight 

 somewhat difficult to understand owing to their having become altered 

 in the course of development. In )our own fore-arm the bones can 

 be rotated on one another, so tliat the thumb can be made to point 

 uutw ards or inwards ; while in ihe rabbit the first digit has permanently 

 the same position, pointing inwards. To understand this, extend your 

 arm outwards wiUi the thumb pointing away from the ground. The 

 back of the hand and arm, continuous wdtlr the dorsal surface of the 

 body, or back, is its dorsal surface ; the palm of the hand, and the sur- 

 face (jf the arm continuous with the chest, is its vcti/ral surface ; the 

 border of the arm and hand continuous with the thumb is the pre- 

 axial border ; anti that cturtinuous with the little finger the postaxial 

 border. This pijsition is called the position of supination : if 

 the fwrc-arni and hand be now rotated, s(j that the thumb points 

 inwards, the position is that of pronation. Wliile in this position, 

 bend the elbow at right angles and bring it inwards close to the boil) ; 

 the preaxial bnrder of the hai^d. will now be on the inner side, and 

 an examination of the bones of the fore-arm shows that they cross 

 on another. It is in this position that the fiones of the rabbit's fore- 

 limb arc |iermanently fixed (Fig. lOi, and compare Fig. S). 



The ]jru\imal cxtremit\' of the liiiiiterus bears a rounded 

 head fur articulation with the glenoid cavity, in front uf 

 which is a groo\e for the tendon of the biceps muscle 

 (j). 6[) ; and certain titherosilics for the attachment of mus- 

 cles will also be ol)ser\cd. Its distal e\trcmit\' jjresents a 

 large, pullc)-like surface or troihlca for the articulation of 

 the bones of the fore-arm, and a deep depression or fosi'U 

 perforated by a foramen, on its posterior side, lur the recep- 

 tion of the end of the ulna. 'I'he radius is the shorter, 

 inner (prea.xial) bone of the fore-arin, and is slight])- curved. 



