1 164 



HUMAN ANATOMY. 



the entire choroid plexus of the lateral ventricle, the ependyma is torn away and an 

 artificial opening is produced, which may be followed, as a curved narrow cleft, from 

 the lower end of the inferior horn upward above the hippocampus and over the 

 dorsal surface of the thalamus, beneath the fornix and the splenium, to the exterior of 

 the hemisphere. When traced forward from its attachment along the upper surface 

 of the thalamus, the line of the reflection of the ependyma, taenia chorioidea, leads 

 to just above the foramen of Monro (Fig. 966), where it is joined by the similar 

 line of the opposite ventricle. From this point the choroidal line of ependymal 

 reflection is continuous with the taenia thalami, the sharp ridge which marks the 

 junction of the superior and mesial surface of the thalamus (page 1119). Leaving 

 the surface of the latter along this ridge, the ependymal layer covers the under side 

 of the velum interpositum, as well as the double row of vascular villous projections, 

 which, one on each side of the mid-line of the roof, constitute the choroid plexus 

 of the third ventricle (Fig. 974). Although similar in its general structure, this 

 vascular fringe is much smaller and less conspicuous than that within the lateral 

 ventricle. 



It is evident from the foregoing description, that communication between the third and 

 lateral ventricles is completely interrupted by the attachment of the ependymal layer and that 

 at only one place, the foramen of Monro (page 1060), does such communication exist. It is 

 of interest to note that these several lines of ependymal reflection — the taenia chorioidea, the 

 taenia thalami and the tania fornicis and its prolongation, the tcenia fimbriae — form a contin- 

 uous line which morphologically marks the transition of the thicker nervous part of the wall of 

 the hemisphere into the thin and atrophic area, which early undergoes an invagination leading 

 to the production of voluminous vascular structures later seen in the definite choroid plexuses 

 of the lateral and third ventricles. Along the margin of the choroidal fissure, at which such 

 invagination primarily occurs, the white matter of the hemisphere becomes condensed into the 

 tract of the fornix and its downward prolongation, the fimbria. These structures, together 

 with the reflected ependyma and the septum lucidum, are regarded, therefore, as modified 

 parts of the mesial surface of the hemisphere. 



Fig. 1003. 



C C 



The inferior horn (cornu inferius), also caWed the descc?idi?ig- horn, begins above 

 at the hind-end of the body of the ventricle, thence curves backward and outward 

 around the thalamus, and sweeps downward and forward and a little inward (Fig. 

 1000) into the temporal lobe well towards its tip, which, however, it fails to reach by 



about 2 cm. Its descent is not 

 only very abrupt, but limited 

 for the most part to almost a 

 vertical plane ; hence this part 

 of the ventricle does not diverge 

 to any considerable extent be- 

 yond the plane of the gyrus hip- 

 pocampi, just to the outer side 

 of which the lower end of the 

 inferior horn lies. The 7'oof of 

 this cornu is formed chiefly by 

 the tapetum of the corpus cal- 

 losum, and within it descend the 

 recurved attenuated tail of the 

 caudate nucleus and the taenia 

 semicircularis to join a rounded 

 mass of gray matter, the amyg- 

 daloid nucleus (page 1172), 

 which lies embedded within the 

 temporal lobe, slightly above 

 in front of the lower end of the inferior horn (Fig. 967). The floor of 



Taenia chorioidea 



Tsenia fornicis 



Taenia thalami 



Choroid plexus 

 of III ventricle 



Diagram showing relation of pial tissue in velum interpositum to 

 ependyma in lateral and third ventricle ; ependyma is represented by 

 red line; c, c, corpus callosnm; F, fornix; vv. so-called ventricle of 

 Verga ; C, T, caudate nucleus and thalamus. 



and 



the inferior horn begins above in the triangular area, the trigonum ventriculi, 

 between the diverging inferior and posterior horns. The greater part of this field is 

 occupied by a low convexity, the collateral protuberance (trigonum collaterale), 

 which is continued into a rounded ridge, the collateral eminence (eminentia 



