PLATE XLVIII. NATURAL SIZE. 



INTERIOR OF SKULL, TENTORIUM, CIRCLE OF WILLIS, 

 FIRST VIEW OF ORBITS. 



In this plate th6 calvariuin 1ms been removed in the usual way by a horizontal 

 saw cut, and the brain carefully removed so as to leave intact the arteries composing the 

 circle of Willis in their normal positions with relation to the nerves. The best way of 

 doing this in the ordinary dissecting-room subject is to use a stream of water either 

 from a syringe or tap and allow it to wash away the brain. On the left side the attached 



<>f the tentorium has been cut into to expose the lateral sinus. 



The orbits were then opened in the usual manner, but if the dissector wishes to 

 preserve the pulley of the superior oblique in situ, it will be best to place the tip of a 

 finger in the inner corner of the orbit and saw through directly external to it. 



The arteries comprising the circle of Willis are, the basilar behind dividing into 

 the posterior cerebrals ; the internal carotids on either side in front giving off the 

 anterior cerebrals, which are joined in front by a short trunk of somewhat variable size, 

 the anterior communicating, and the middle cerebrals which are connected by means of 

 the posterior communicating with the posterior cerebrals ; the posterior communicating 

 are very variable in si/e and may not be of the same calibre on both sides of the body. 



Thus is established a great circle of anastomosis at the base of the braia. 



