THIRD VENTEICLE. 



483 



cerebri and hemispheres. The anterior portions of the optic 

 thalami approximato most closely. Their upper Surfaces are 

 convex and free, and their posterior surfaces project into the 

 descending cornua of the lateral ventricles. Between the 

 tlir.lami and the crura cerebri are rounded grey prominences, the 

 ryr'pora geniculata, two on each side, the innermost of which 

 connect the thalami with the nates, 

 and the outermost,, which are the 

 larger, with the testes. 



THIRD VENTRICLE. 



The third ventricle is the space 

 "between the optic thalami, which form 

 its lateral walls, seen on removing the 

 fornix and velum interpositum, which 

 form its roof; its floor being formed 

 by the tuber cinereum, corpus albicans, 

 locus perforatus posticus, and lamina 

 cinerea; its anterior boundary is 

 known as the lamina terminalis. Three 

 commissures^ anterior, middle, and 

 posterior, cross this ventricle. The 

 anterior is a bundle of white fibres, 

 which forms the anterior boundary of 

 the ventricle, and unites the corpora 

 ntriata behind the pillars of the fornix ; 

 the middle, consisting of grey matter, 



is the Orey or soft commissure, which Fourth ventricle; +, Aqueduct of 



Btretch^es betweea the thalami; and f^^J^^^^T^,':^,-^ 



the posterior, which is white, and also minalls; C.S., corpus atriatum; Tft., 



. , , , . -, . Optic thalamus; Pn., Pineal gland; 



unites the tnalami, crosses tne pOSte- Jlf,&., Middle brain ; C7&.,CerebeUunj.: 



rior part of the ventricle in front of Jif.o..Meduiia oblongata ori^ of 



* nerves:— I., Olfactory; il., Optic. 



the pin^ gland. There are three 



openings into this ventricle — Ist, Between the anterior and 

 middle commissure, in the centre of the floor, a deep pit or 

 cavity, the iter ad infundihulu/ni, leads to the infundibulum ; 

 27id, Between the grey commissure and summit of the fornix, 

 the foramen of Monro leads into the lateral ventricles ; and Srd, 

 The aqueduct of Sylvius, or iter e tertio ad quartum verdricu- 

 lum, which leads into the fourth ventricle. Through these 



Fio. 180. 



Horizontal and diagramatic section^ 



showing the cavities of the brain. 



1, Olfactoiy ventricle; 2, Lateral 



ventricle; 3, Third ventricle; 4. 



