90 PERCIVAL BAILEY 



continues to the foramen interventriculare where it divides 

 into two parts, the lateral part passing forward in the floor 

 of the lateral ventricle (the intermediate root of the corpus 

 striatum, figs. 2 and 23, c.s.i.r.), and the medial part passing 

 through the foramen interventriculare, forming its floor, and 

 extending in the lateral wall of the third ventricle behind the 

 lamina terminalis as far as the recessus preopticus (fig. 18, 

 c.s.m.r.). It is very likely that this elevation which I have just 

 described as the medial root of the corpus striatum contains in 

 its lower end other things besides striatal tissue. I shall con- 

 tinue to describe the entire elevation as the medial root of the 

 corpus striatum, following the usage of His, and shall not enter 

 into a discussion of its internal structure. 



Above the taenia fornicis on the ventricular surface of the 

 medial hemisphere wall may be seen an elevation (fig. 19, hip. ) 

 extending from the posterior pole of the hemisphere just above 

 the choroid plexus, and beyond it over the foramen interventri- 

 culare. This is the anlage of the hippocampus, at least in part. 

 There is corresponding to it on the outer pial side of the hemi- 

 sphere wall, a shallow groove (figs. 1 and 2,f.a.). This groove is 

 not due to the folding in of a thin weak place in the wall, for the 

 wall at this point is very definitely thicker (fig. 27). 



Turning now to the wall of the third ventricle, we find just 

 below the tela chorioidea diencephali a low ridge (fig. 18, n.h.) 

 extending from the epiphyseal evagination almost to the velum 

 transversum. This is the habenula. From its anterior end a 

 sharp ridge runs backward and downward to the subthalamus 

 (fig. 18, h.s-t.r.). Above this ridge, the wall is shrunken and 

 thin up to the habenular thickening. Below the ridge, is an 

 elevation (fig. 18, th.l) which extends upward and forward in 

 front of the habenula toward the velum transversum. 



The sulcus limitans is indicated on figure 18 by a dotted line 

 running above the tegmentum and subthalamus, below the 

 elevation last mentioned (fig. 18, th.l) and behind the corpus 

 striatum to the preoptic recess. Just back of the corpus stria- 

 tum and between it and the hypothalamus, the sulcus limitans 

 runs into a very deep recess (fig. 2) . 



