THIRD VENTRICLE. 



483 



cerebri and hemispheres. The anterior portions of the optic 

 thalami 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 genicidata, 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 jjosticus, and lamina 

 cinerea ; its anterior boundary is 

 known as the lamina terminalis. Three 

 comviissures, 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 

 striata behind the pillars of the fornix ; 

 the middle, consisting of grey matter, 

 is the grey or soft commissure, which 

 stretches between the thalami ; and 

 the ijosterior, which is white, and also 

 unites the thalami, crosses the poste- 

 rior part of the ventricle in front of 

 the pineal 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 infundibidum, leads to the infundibulum ; 

 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 tertlo ad qiiartum ventricu- 

 lum, which leads into the fourth ventricle. Through these 



Fio. ISO. 

 Hurizoutal and diagramatic section, 

 showing tlie cavities of the brain. 

 1, Olfactory ventricle; 2, Lateral 

 ventricle; 3, Third ventricle; 4, 

 Fourth ventricle; +, Aqueduct of 

 Sylvius; Olf., Olfactory lobes; P.M., 

 Foramen of Monro ; L.t., Lamina ter- 

 minalis ; C.S., Corpus striatum; Th., 

 Optic thalamus; Pn., Pineal p;land; 

 M.b., Middle braiu ; Cb., Cerebellum ; 

 M.O., Medulla oblongata, Origins of 

 nerves :— /., Olfactory ; II., Optic. 



