THIRD VENTRICLE. 



483 



cerebri and hemispheres. The anterior portions of the optic 

 thaJami approximate most closely. Their upper surfaces are 

 convex and free, and their posterior surfaces project into the 

 descending cornua. of the lateral ventricles. Between the 

 thalami and the crura cerebri are rounded grey prominences, the 

 corpora 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. 



fir. 



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, c^irpus albicans, 

 locus perforatus posticus, and lamina 

 cinerea; its anterior boundary is 

 known as the lamina terminalis. Three 

 cwnmissures, 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 corpbra 

 striata behind the pillars of the fornix ; 

 the middle, consisting of grey matter, 



is the grey or soft COm'misSV.re, which Fourth ventricle; +, Aqueduct of 



stretches between the thalami; and syivius; w olfactory lobes; j- at.. 



' Foramen of Monro; i.f.. Lamina ter- 



the posterior, which is white, and also nunaiis ; c.s., corpus striatum ; tk., 



•a J.T. xT. 1 • xT- J. Optic thalamus; Pn., Pineal gland; 



umtes the tnalami, crosses tne poste- Af.6., Middle brain ; ct., cerebellum.; 

 rior part of the ventricle in front of ^■^- Medulla oblongata, origins of 



*, 1 mi 1 nerves:— /., Olfactory ;//., Optic. 



the pmeaj gland. There are three 



openings into this ventricle — 1st, Between the anterior and 

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

 cavity, the iter ad infwndibulum-, leads to the infiindibulum ; 

 2nd, 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 verutricu- 

 lum, which leads into the fourth ventricle. Through these 



Fig. 180. 



Horizontal and diagramatic section, 



showing the cavities of the brain. 



1, Olfactory ventricle; 2, Lateral 



ventricle; 3, Third ventricle; 4, 



