THE TELENCEPHALON. 



1163 



inner margin of this zone the ependyma leaves the surface of the thalarnus and 

 passes onto the villous projections (Fig. 1003) of pia mater containing the convolu- 

 tions of blood-vessels of which the choroid plexus is composed. Each projection, 

 (glomus chorioideum) consists of: (i) a capillary complex formed by the terminal 

 twigs of the anterior and posterior choroidal arteries, the former of which gains the 

 interior through the choroidal fissure in the inferior horn of the lateral ventricle ; 

 (2) the connective tissue of the pia ; and (3) the ependymal layer (lamina chorioidea 

 epithelialis), which everywhere invests the pial plications and, therefore, excludes the 

 vascular tissue from actual entrance into the ventricular cavity. While inconspicuous 

 and often overlooked, this ependymal layer is of much morphological significance, 

 since it represents all that persists in certain localities of the true wall of the hemi- 

 sphere. After leaving the surface of the thalarnus and investing the vascular pro- 



FIG. 1002. 



Septum lucidum 

 Anterior end of fornix. cut 



Hippocampus 

 Velum interpositum 



Choroid plexus in inferior 

 horn of lateral ventricle 



Splenium, under surface 



Posterior horn of lateral 

 ventricle 



Lateral parts of fornix, 

 under surface 



Corpus callosum 



Caudate nucleus 



Choroid plexus, overlying 

 foramen of Monro 



Vein of corpus striatum 

 Choroid vein in plexus 



Veins of Galen 



Crus of fornix and posterior 

 forceps of corpus callosum, 

 cut 



Under surface of fornix, 

 Lyra 



Cut anterior end of fornix 



Dissection of brain, showing velum interpositum and choroid plexuses of lateral ventricles; seen from above 

 after removal of corpus callosum and fornix; latter has been cut through in front and behind and turned back, 

 exposing its under surface. 



jections constituting the choroidal plexus, the ependyma becomes attached along 

 the taenia fornicis to the thin lateral margin of the fornix, beneath which the velum 

 interpositum protrudes to expand into the choroid plexus within the body of the 

 ventricle. 



The plexus is not confined to this part of the space, but follows the hippocampus 

 to the lower end of the inferior horn. The relation of the vascular pial tissue to 

 this extension of the ventricle is, however, the same as within the body, since the 

 glomeruli here, as there, are completely invested by the ependyma, which they 

 invaginate along a groove, the choroidal fissure, above the hippocampus, in 

 the same manner as they do higher in the ventricle. The line of attachment of the 

 ependyma to the wall of the horn, taenia fimbriae, follows the recurved tail of 

 the caudate nucleus, just beneath which it lies, on the one hand, and the thin mesial 

 edge of the fimbria (the continuation of the fornix) on the other. On pulling out 



