876 



THE NERVOUS SYSTEM 



plexus of the lateral ventricle curves posteriorly and inferiorly into the inferior 

 cornu, being especially well developed at the region of its entrance into the latter, 

 into what is called the chorioid glomus. 



Though apparently lying free in the ventricle, the chorioid plexus is invested throughout 

 by a layer of epithelium, the epithelial chorioid lamina, which is adapted to all its unevennesses 

 of surface and which is a continuation of the ependymal lining of the remainder of the ventricle 

 — continuous, on the one hand, with that of the lamina affixa and thalamus, and, on the other, 

 with the epithelial covering upon the upper surface of the taenia of the fornix and fimbria. 



The posterior cornu of the lateral ventricle is a crescentic cleft of variable length, 

 convex lateralward, which is carried backward from the posterior end of the body 

 of the ventricle and, curving medialward, comes to a point in the occipital lobe. 

 Its roof and lateral wall are formed by a portion of the posterior radiation of the 

 corpus callosum, which forms a layer, from its appearance known as the tapetum. 

 In transverse sections of the occipital lobe (fig. 699) the tapetum appears as a 



Fig. 



689. — Diagrammatic Transverse Section of Prosencephalon through Bodies op 

 Lateral Ventricles and Middle op Thalamencephalon. 



Fifth ventricle 



Fornix 



Lateral ven 

 tricle 



Caudate 

 nucleus 

 Lamina affixa 

 Vena ter- 

 minalis 

 Stria ter- 

 minalis of 

 thalamus 

 < Puta- 

 « v> I men 



II 

 a 3 I 



^ ° Globus 

 I pallidus 



Caudate 

 nucleus 

 Chorioid 

 plexus 

 Inferior cornu 

 of lateral 

 ventricle 



Fimbria 



Dentate gyms 

 or fascia 



Chorioid 

 plexus 



Chorioid tela 

 Thalamus 



Third 

 ventricle 



Mammillo- 

 thalamic 

 fasciculus 



Internal 

 capsule 



thin lamina of obliquely cut white substance immediately bounding the cavity, 

 while outside the tapetum occurs a thicker layer of more transversely cut fibres, 

 the occipito-thalamic radiation. In the medial or inner luall of the posterior horn 

 run two variable longitudinal eminences: — (1) The superior of these is the bulb of 

 the posterior cornu, and is formed by the occipital portion of the radiation of the 

 corpus callosum (splenium), which bends around the impression of the deep pa- 

 rieto-occipital fissure, and, hook-like, sweeps into the occipital lobe. In horizontal 

 sections these fibres, together with the splenium and the similar fibres into the 

 opposite occipital lobe, form the figure known as the forceps major. (2) The 

 inferior and thicker of the eminences is the hippocampus minor [calcar avis] 

 (cock's spur), and is due to the anterior part of the calcarinc fissure, by which the 

 wall of the hemisphere is projected into the ventricle. The posterior horn, like 

 the anterior, is not entered by the chorioid plexus. 



The inferior cornu. — In its inf(!rior and slightly lateral origin from the region 

 of junction between the body of the ventricle and the posterior cornu, the inferior 

 horn aids in i)roducing a somewhat triangular dilation of the cavity known as the 

 collateral trigone. Beginning as a part of the trigone, the cavity of this horn at 

 first passes posteriorly and lateralward, but then suddenly curves anteriorly and 



