Il62 



HUMAN ANATOMY. 



nterior horn 



almost completely masked by the overlying choroid plexus; (4) the choroid plexus 

 of the lateral ventricle ; and (5) the lateral edge of \hzfornix. The caudate nucleus 

 will be subsequently described (page 1169), suffice it to note its rapid diminution 

 in size, as it curves backward and downward on the roof of the inferior horn. 



The tasnia semicircularis is more or less hidden by the superficially placed vein 

 of the corpus striatum (vena terminalis), which lies immediately beneath the epen- 

 dyma and shows as a distinct sinuous ridge. Receiving tributaries from the adjacent 

 parts of the thalamus, the caudate nucleus and the walls of the anterior horn, includ- 

 ing the septum lucidum, the vein passes to the foramen of Monro, where, meeting 

 with the choroid vein at the apex of the velum interpositum, it forms with the last- 

 named vessel the vein of Galen. 



The taenia semicircularis, or stria terminalis, the band-like tract of nerve- 

 fibres occupying the sulcus intermedius, is a part of the complex pathway by which the 

 primary and secondary olfactory centres are united. Its component fibres arise partly 

 in the anterior perforated space and partly in the septum lucidum from which centres, 

 reinforced by fibres from the anterior commissure, they converge towards the sulcus 



intermedius which they 



FIG. 1001. then follow. After leaving 



the body of the lateral 

 ventricle they descend with- 

 in the roof of the inferior 

 horn, in close relation to 

 the recurved tail of the 

 caudate nucleus, to end 

 within the amygdaloid 

 nucleus (page 1172). 



The choroid plexus 

 ( plexus chorioideus ventriculi 

 lateralis) is a convoluted 

 vascular complex which 

 occupies the lateral margin 

 of the pial sheet, the velum 

 interpositum, within the 

 body of the lateral ventricle, 

 and, in addition, descends 

 along the inferior horn of 

 the lateral ventricle to its 

 tip. In order to understand 

 the relations of the choroid 

 plexus, those of the larger 

 sheet, of which it is part, must be described. The velum interpositum (tela 

 chnrioidca ventriculi tertii) is a delicate sheet of pia mater whose upper surface is 

 exposed after removal of the corpus callosuin and the body of the fornix. When 

 viewed from above (Fig. 1002) it is triangular in outline, its apex lying at the 

 foramen of Monro and its lateral basal angles extending into the descending horns 

 of the lateral ventricles. Its inferior surface forms the roof of the third ventricle, 

 beyond which on each side it covers the greater part of the upper surface of the 

 thalamus and, in turn, is overlaid by the fornix. Behind, the velum interpositum is 

 continuous beneath the splenium of the corpus callosum with the pia mater investing 

 the external surface of the hemisphere. This relation readily gives rise to the 

 impression that the- pial tissue has gained entrance to the ventricles by growing 

 forward through the cleft beneath the splenium and the fornix. That such, however, 

 is not the case will be pointed out later, when the development of this sheet is 

 considered (page 1194). The relation of the velum interpositum to the ventricular 

 ravities should be carefully noted by tracing the ependyma from the caudate nucleus 

 inward. Leaving the convex surface of this structure, the ventricular lining covers 

 the sulcus terminalis with its vein, and passes for a short distance over the adjoining 

 outer part of the upper surface of the thalamus. This zone (lamina affixa") narrows 

 in front and behind, and where broadest measures from 5-7 mm. Along the 



Lateral 

 recess 



Cast of ventricles, viewed from above. X 



Posterior 

 horn 



(ftetzius.) 



