272 Suppofed Seat of tie Soul. [Book IX. 



fore part with the pafiage between the two lateral ven- 

 tricles, and fends down from its under and fore part a 

 paflage through the infundibulum j it has a communi- 

 cation backwards with the fourth ventricle. 



The infundibulum is a fmall medullary canal, fituated 

 between the bafe of the anterior pillar of the fornix, 

 and the anterior part of the union of the thalami ner- 

 vorum opticorum. It runs downwards, and terminates 

 by a fmall membranous canal in a foftifh body, fftuated 

 in the fella turcica of the fphenoidal bone, and called 

 glandula pituitaria. This fubflance was fo named by 

 the ancients, from its fuppofed office of cleanfmg the 

 brain from ferous fluids. Its real ufe is wholly 

 unknown. In ruminant animals it is much larger than 

 in man. 



The nates and teftes, or as they are otherwife deno- 

 minated, tubercula quadrigemina, are four tubercles, 

 fituated behind the union of the thalami nervorum 

 opticorum, adhering to each other. They are ex- 

 ternally white, and their internal fubftance is greyifh. 

 Between the two anterior tubercles and the convex 

 part of the thalami nervorum opticorum is ah interface 

 called foramen commune pofterius. This, however, 

 is clofed by the pia mater, a,nd does not open into any 

 cavity. 



Above the tubercula quadrigemina, and behind the 

 thalami nervorum opticorum, is fixed the pineal gland. 

 This body is of an oval form, about the fize of a pea, 

 and is connected to the lower part of the thalami by 

 two very white medullary pedunculi. It feems to be 

 moftly formed of cortical fubftance, particularly at its 

 upper part, and adheres clofely to the plexus choroides, 

 with which it is covered. This fmall body has been 

 rendered famous by Defcartes,.who fuppofed it to be 

 the feat of the foul. It is often fcund, on being cut 



into, 



