PAETS DEEIVED FKOM THE DIENCEPHALON. 



617 



matter which surrounds the aqueduct is directly continuous with the gray matter 

 3f the substantia perforata posterior and tuber cinereum, and in this way it comes 

 . bo the surface in the base of the brain. The optic chiasma crosses the floor in front 

 ind marks the place where the latter becomes continuous with the anterior wall 

 sf the cavity. The anterior wall of the third ventricle is formed by the lamina 

 fcerminalis, which extends upwards from the optic chiasma. The anterior com- 

 missure, as it crosses from one side to the other, projects into the ventricle, but, of 

 bourse, it is excluded from the cavity by the ventricular epithelial lining. It may 

 be taken as indicating the place where the roof joins the anterior wall. The roof 

 rf the third ventricle is formed by a thin epithelial layer which stretches across the 

 median plane from one tsenia thalami to the other, and is part of the thin epithelial 

 lining of the cavity. Applied to the superior surface of the epithelial roof 



Epithelial roof of third ventricle 



Foramen in terventriculare | Lamma commissune hi pp O campi 

 oina commissure hippocampi at the attach- | } . 



uent of the epithelial roof of third ventricle i j Ta?nia thalami 



Corpus callosum ,' j 

 Columna fornicis 1 ; 

 Septum pellucidum \ '.''. 

 Anterior commissure^ -\- - J T\~ j ~-J 

 -rnuii oorporis callosi^^-^""^ ' i i / j i 

 on "iris callosi 



Vena cerebri interna 

 \ Plexus chorioideus ventriculi tertii 

 \ } Commissura habenulae 

 \ I Recessus suprapinealis 

 i-^J i Pineal body 



l f I i """]>J^Splenium corporis callosi 

 I ;xNk Lamina quadrigemina 

 '-^ / ^quaeductus cerebri 



Vena magna cerebri 



*.. Velum medullare anterius 



Lobulus centralis cerebelli 

 / Culmen cerebelli 

 Ik./ 



Paraterminal body-- 

 Lamina terminalis- 



Optic chiasma 



Infundibulum 



Fissura prima cerebelli 



/Fourth ventricle 

 .Attachment of 

 ''epithelial roof 



iNodulus 

 cerebelli 



Hypophysis 



Massa intermnd 

 Sulcus hypothalamicus ; 



Corpus mamillare / / 

 Oculomotor nerve/ 

 Posterior commissure , 

 Tegmentum (mesencephali) ; 

 Pons 



Pyramid--'' 



Fourth ventricle' 



Central canal-' 3 

 Decussation of pyramid*"' 



.Pyramis 

 cerebelli 



Uvula cerebelli 

 '%) Tonsilla cerebelli 

 Edge of apertura medialis 



Chorioid plexus of fourth ventricle 

 (the pointing ]ine passes through 

 the apertura medialis) 



FIG. 544. THE PARTS OP THE BRAIN CUT THROUGH IN A MEDIAN SAGITTAL SECTION. 

 The side walls of the ventricular cavities are also shown. 



the fold of pia mater, termed the tela chorioidea, and the roof is invaginated 

 into the cavity along its whole length by two delicate chorioid plexuses, which 

 hang down from the under surface of this fold. When the pia mater is removed 

 the thin epithelial roof is torn away with it, leaving only the lines of attach- 

 ment in the shape of the taenia thalami (Fig. 549). 



The side wall of the third ventricle is formed for the greater part of its 

 extent by the medial surface of the thalamus, covered by a thick layer of central 



Y matter continuous with the central gray matter of the mesencephalon. A 

 little in front of the middle of the ventricle the cavity is often crossed by the 

 massa intermedia, which connects the thalami one with the other, and in front of 

 this the columna fornicis is seen curving downwards and backwards in the side 

 At first the bulging which it forms is distinctly prominent, but it gradu- 

 ally subsides as the strand, on its way to end in the corpus mamillare, becomes 

 more and more sunk in the gray matter on the side of the ventricle. 



