120 THE CEREBRUM. 



sphere wall, covers it. The thalamus will be described with 

 the third ventricle and inter-brain. 



The chorioid plexus (plexus chorioideus, Figs. 35, 36 and 37) 

 of the lateral ventricle is the vascular border of the chorioid tela 

 of the third ventricle. It projects, laterally, from beneath the 

 fornix and its crus through the chorioidal fissure into the floor 

 of the central part of the ventricle and the inner wall of the inferior 

 horn. The epithelium, above mentioned, invests it; and it borders 

 the fornix like a ruffle. It is called chorioid plexus (chorion, 

 a membrane) because it is membrane-like. At the junction of 

 the central part and inferior horn of the lateral ventricle the 

 chorioid plexus presents a large skein-like mass called the glomus 

 chorioideum (Fig. 36). The anterior chorioidal artery from the 

 internal carotid and the postero-lateral chorioidal, a branch of 

 the posterior cerebral, supply the plexus. The former pierces 

 the temporal lobe and enters the apex of the inferior horn of the 

 ventricle; the latter passes in through the transverse and chorioidal 

 fissures of the cerebrum, following the chorioid tela. The chori- 

 oidal vein carries the blood away. At the foramen interventricu- 

 lare, it is joined by the terminal vein of the striated body and the 

 veins of the septum pellucidum and forms the internal cerebral 

 vein. The internal cerebral vein courses backward in the chorioid 

 tela and unites with its fellow of the opposite side, proximal to 

 which union it receives the basilar vein ; and then the great cerebral 

 vein (of Galen), uniting with the inferior sagittal sinus, forms the 

 straight sinus. 



The floor of the central part of the lateral ventricle is com- 

 pleted by the superior surface of the fornix. 



The horns of the lateral ventricle are three in number; the 

 anterior, inferior and posterior (Figs. 39, 40 and 41). 



The anterior horn (cornu anterius, Figs. 35, 36 and 73) projects 

 from the central part of the ventricle forward and outward around 

 the head of the caudate nucleus. It is the ventricle of the frontal 

 lobe and is deep and narrow. Its boundaries are as follows: 



Roof Corpus callosum (forceps minor). 



Floor Rostrum. 



Anterior wall Genu. 



