854 THE NERVOUS SYSTEM 



verse sections of the occipital lobe (fig. 6 13) the tapetum appears as a thin lamina of 

 obliquely cut white substance immediately bounding the cavity, while outside the 

 tapetum occurs a thicker layer of mure transversely cut fibres, the occipito-t.halamic 

 radiation. In the medial or inner wall of the posterior horn run two variable longi- 

 tudinal 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 (sple- 

 nium), which bends around the impression of the deep parieto-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 or calcaravis (cock's .spur), anil is due to the anterior part of 

 the calcarine fissure, by which the wall of the hemisphere is projected into the ven- 

 tricle. The posterior horn, like the anterior, is not entered by the chorioid plexus. 



The inferior cornu. In its inferior and slightly lateral origin from the region 

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

 horn aids in producing 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 backwards and lateraKvards, but then suddenly curves downwards and for- 



Fio. 636. DISSECTION OF RIGHT TEMPORAL LOBE SHOWING THE MEDIAL WALL OF THE END 

 OF THE INFERIOR HORN OF THE LATERAL VENTRICLE. (From Spalteholz.) 



DIGIT A TIOXS OF 

 IIIPPOL'AMPLV >, 



FIMBRIA OF HIPPO- 



HIPPOCAMPAL 

 FISSURE 



]> K. \TATE FASCIA ,^ 



' Uf.r.A Tl:l!AL 



SUBSTAXTIA RETIC- . 

 VLARIS ALBA '' 

 (ARXOLDI) 



HIPPOCAMPAL GYRUS- 



TsEXIA FI.VBRI+E 



COLLATERAL FISSURE 



wards into the medial part of the temporal lobe nearly parallel with the superior tem- 

 poral sulcus. Above, it follows the curve of the posterior pillars of the fornix and 

 fimbria; below, it does not extend to the temporal pole by from 2 to 3 cm. The roof 

 and lateral wall are, for the most part, like those of the posterior horn, being formed 

 by the tapetum, but medianwards a strip of the roof is formed by the attenuated, infe- 

 rior prolongation, or tail, of the caudate nucleus, together with the lower part of the 

 stria terminalis of the thalamus. At the end of the inferior horn the roof shows a 

 bulging, the amygdaloid tubercle, situated at the termination of the tail of the cau- 

 date nucleus. This bulging is produced by the amj/gdaloid nucleus, an accumulation 

 of grey substance continuous with that of the cortex of the temporal lobe, and which 

 gives origin to the greater part of the longitudinal fibres coursing in the stria termi- 

 nalis of the thalamus. 



In the medial wall and floor of the inferior horn the following structures are 

 shown: (1) In the posterior or trigonal part of the floor is the longitudinal col- 

 lateral eminence, a bulging, very variable in development in different specimens, pro- 

 duced by the collateral fissure. This is often pronouncedly in two parts, a posterior 

 prominence corresponding to the middle portion of the collateral fissure and an anterior 

 prominence (less frequent) produced by the anterior part of the fissure. (2) Medial 

 to this eminence lies the inferior extension of the chorioid plexus, usually more vol- 



