Till: I'lA MATI'Ai 



897 



The tela chorioidea of the third ventricle, or velum interpositum, i.s u tri- 

 angular duplication of the pia n inter which extends bet ween t lie foniix aliove and the 

 thahimi and third ventricle below, and in front ends blindly at the tnterveatrioulai 

 foramina. In the transverse cerebral lissiire the layers of pia forming the tela are 

 s 'pai-ale. the upper being t he pia of t he under surface of t he corpus callosuni and con- 

 tinuous with t hat of the tend trial surfaces of I lie occipital lobes; t he lower being con- 

 tinuous into the pia enfolding the epiphysis, and covering the niesencephalon, 

 anterior medullary velum, and cerebellum. The layers forming the portion of the du- 

 plication which roofs over the third ventricle are loosely adherent to each other and 

 form the tela chorioidea proper of that ventricle. The upper surface of this portion 

 is in relation with the fornix and its lower surface, covered by the epithelial chorioid 



Tin. 068. HORIZONTAL I>ISM:< M<>\ OK Tin < \i SHOWING THE TELA CHOKIOIDEA or 



THE THIRD VENTRICLE. 



(From a mounted specimen in (lie Anatomical 1 )uptirtment of Trinity College, Dublin.) 

 The fornix has been removed to show the tela chorioidea. 



CAUDATE 



\l 



CKRE- 

 BSLLtm 



COKI-rs 

 CALLOSUM 



( in -v. c//')// ) 



SKPTUM 

 PELLUCI- 

 DUM 



FIFTH 



viMRICLE 



STRIA TER- 

 MIXAIM 

 (II-' THALA- 



trus 



THALAMVS 



Tela 



chorioidea 

 (velum Inter- 

 positum) 



i'ltnl InidpleXVX 



FIMBK1A 

 HIPPOCAM- 

 J'Cfi MAJOR 



EMIXEXTIA 



fin. I, i /'/-:/;- 

 A US 



CALCAR 

 AVIS 



lamina, lies laterally over the superior surfaces of both thalami, and mesially forms the 

 roof of the third ventricle between them. Between the two layers of this portion, 

 and embedded in a small amount of the spongy subarachnoid tissue retained between 

 them, are the two veins of ( ialen. the internal cerebral veins. Posteriorly these veins 

 unite in the region of the epiphysis to form the single great cerebral vein (vena 

 cerebri niagna). Anteriorly the veins of Galen receive the veins of the septum pellu- 

 cidum from each lamina of the septum pellucidum above, and also the terminal vein 

 (vein of corpus striatum), lying in the stria terminalis of the thalamus, empties into 

 them from each side. 



The tela chorioidea or velum interpositum extends laterally between the fornix 

 and fimbria above and the stria terminalis of the thalamus below into each lateral 

 57 



