THE RABBIT. 365 



and connecting the semi-lunar cartilages (97) with one or 

 other bone. 



The posterior ligament extends from the inner (post-axial) face of 

 the internal condyle of the femui obliquely downwards to about the 

 middle of the posterior edge of the articular surface of the tibia : the 

 anterior crucial ligament extends from the inner (pre-axial) face of 

 the external condyle of the femur to the anterior part of the articular 

 surface of the tibia, near the middle line : the posterior crucial 

 ligament extends from a point within the external coudyle of the femur 

 and immediately proximal to the attachment of the posterior ligament, 

 obliquely downwards and outwards to the posterior end of the post- 

 axial semi-lunar cartilage ; it is continued from the anterior end of the 

 same cartilage, passes inwards in front of the tibial attachment of the 

 anterior crucial, and is attached near the inner border of the articular 

 surface of the tibia : the internal or pre-axial semi-lunar cartilage has a 

 ligament at its anterior end which crosses in front of the posterior 

 crucial to be inserted into the articular surface of the tibia near the 

 middle of its anterior region ; a similar ligament from the posterior end 

 of the cartilage is inserted immediately in front of the tibial attachment 

 of the posterior ligament. 



LVI. In the brain, dissect off the pia mater, taking 

 special care not to remove the nerve roots ( 

 488-495) or the arteries ( 476) with it : the latter 

 may, however, be removed as soon as seen. 

 Make out the following points without further 

 dissection : l 



476. The circle of Willis, an arrangement of arteries 

 on the base of the brain, due to the anastomosis of the 

 vertebrals and internal carotids, and forming a sort of 

 hexagonal figure round the optic chiasma ( 486), infun- 

 dibulum ( 485), and corpus mammillare ( 487). 



The vertebral arteries, entering the foramen magnum, unite on the 

 ventral surface of the medulla oblongata ( 477) to form the median 



1 It is best, if possible, to dissect two brains simultaneously, one 

 fresh, the other well hardened : if only one is used, it should be only 

 moderately hardened say in alcohol of about 70 per cent. 



