98 PERCIVAL BAILEY 



forms more the anterior boundary than the floor of the foramen 

 interventricuhire (fig. 22, c.s.m.r.). The intermediate root is 

 also small, extending beyond the foramen interventriculare in 

 the floor of the lateral ventricle. The intermediate root unites 

 at its posterior end with the medial root, the two being separated 

 from the lateral root by a groove. The lateral root is the lar- 

 gest, and lies more in the floor than in the lateral wall of the 

 ventricle (fig. 24, c.s.l.r.). The two ridges, one formed by the 

 lateral root and the other by the union of the medial and inter- 

 mediate roots, extend backward some distance and then turn 

 sharply downward as a single elevation (fig. 24). 



The hippocampus (fig. 12, hip.) is a broad, slightly thickened 

 portion of the medial hemisphere wall, just above the taenia 

 fornicis. The external sulcus is very shallow and broad. 



The habenular ridge is prominent, extending on the ventric- 

 ular surface of the diencephalon just below the tela chorioidea 

 diencephah from the region of the velum transversum to the 

 epiphysis (fig. 22, n.h.). The ridge extending from the posterior 

 end of the habenula to the tegmentum is also prominent (fig. 

 22, /.r.). 



The most striking feature, probably, is the great thickening 

 of the posterior extremity of the thalamus. The anterior ex- 

 tremity of the thalamus extends well into the foramen inter- 

 ventriculare, some distance anterior to the velum transversum. 



The sulcus limitans is indicated on figure 22 by a dotted line. 

 It is deepest below the posterior pole of the thalamus. Behind 

 the lamina terminalis it is relatively shallow. 



The hypothalamic region is marked mainly by its great length. 

 The mammillary recess is indicated (fig. 22, r.m.) ; the floor plate 

 is wide and thin. The infundibular recess (fig. 22, inf.) is near 

 the optic chiasm but is separated from it by an unmistakable 

 postoptic recess (fig. 22, r.post.). There is no clear external 

 division between hypothalamus and sub thalamus. ♦ 



