THE NERVES. 367 



pons Sylvii) under the splenium fornicis, before the cerebellum, 

 behind the optic tubercles. In front fibres pass to the optic tuber- 

 cles and the commissura posterior of the third ventricle, behind 

 they enter the crura cerebelli superiora. 



620. The Ventricles of the Brain. 



1. The lateral ventricles, ventriculi laterales s. tricornes. Each 

 hemisphere of the cerebrum contains a large L-shaped cavity, 

 which is situated rather towards the basis, separated from the other 

 by the septum pellucidum andfornix only, and in communication 

 by means of theforam. Monroi. It is partly filled with the plexus 

 choroideus. Its roof (centrum semiovale Vieussens) consists of 

 the transverse fibres of the corp. callosum. We distinguish four 

 portions : 



a. Cella lateralis, the lateral chamber, is the central, superior, 

 longitudinal space, which is deeper internally in the angle between 

 septum andfornix on the one side, and thalamus and corp. stria- 

 turn on the other, than externally. Corp. striatum and thalamus 

 form its floor. 



1. Corpus striatum, a club-shaped, gray mass, perforated by 

 veins, which passes backwards into a point, and is situated in 

 a deep fossa on a plane with the insula (foss. Sylvii), on the 

 outer side of thalamus. It is traversed by white striae which 

 penetrate the thalamus. 



2. Thalamus nervi optici, the optic tubercle. Its superior, 

 vaulted, longitudinal surface looks into the lateral ventricle 

 (covered by plexus choroides) ; before it the anterior crus of 

 ihefornix curves downwards ; the corpus striatum surrounds 

 it externally (separated by stria cornea \tcenia semicircu- 

 laris]), with which it forms a centrum for the hemisphere, 

 and is associated with that of the thalamus of the other side 

 by means of commissura mollis ; its internal vertical sur- 

 face forms the lateral wall of the third ventricle ; below, it 

 receives the crus cerebri in an excavation, and behind and in- 

 ternally it joins the posterior commissure. Quite internally 

 on the posterior surface, above the crus cerebri, external and 

 internal to the corpp. quadrigemina, are situated upon either 

 side the two geniculate bodies, the corp. geniculatum intcr- 

 num which passes into one of the anterior, and externum 

 which blends with one of the posterior of the corp. quadri- 

 gemina. 



3. Stria cornea \tania semicircularis], a white, band-like, me- 



