DORSAL VENTRICULAR RIDGE 485 



it into a position lateral to the caudate. There is some indi- 

 cation of the superficial layer of the olfactory area spreading 

 upward beyond the middle ventricular groo\-e (at the point 

 marked l.pyr). 



Passing caudad from this level, in the next section drawn 

 (fig. 8) the same structures are to be seen in the lateral wall. 

 The middle ventricular groove has almost disappeared, however, 

 and the proliferating area for the lentiform nucleus is much 

 smaller. The next section dra^^^l (fig. 7) is the last one in which 

 the lentiform proliferation can be recognized and with it the 

 locus of the i^allial iDorder. In the lower part of the hemispheie 

 the lateral olfactory area is represented by a large collection 

 of cells closely related to the caudate nucleus and the diagonal 

 band. This is the nucleus of the lateral olfactory tract and the 

 next section shows the close relation of l)()th this and the diago- 

 nal band to the stria medullaiis. Caudal to this the nucleus 

 of the latei'al olfactory tract soon disai)pears and the hemispjiere 

 wall ])resents the aj^j^earance of an imdifferentiated pallium, 

 except for the fimbria and tlie thin choioidal area in the meilial 

 wall. 



The next section rostrad from the one first described i)asses 

 through the anterior commissure (fig. 10). The lentiform i)ro- 

 liferation ajij^ears larger, the diagonal band fibers approach 

 those of the olfacto-hypothalamic system. In figiu'es 9, 10. 

 and those of sections farther rostrad, one of the most noteworthy 

 features is the mass of cells proliferating from the deep layers 

 of the pallium. The medial border of the pallium does not 

 show active jiroliferation but in the lateral three-foin*ths many 

 new cells are forming ami these a]:>])ear to be streaming laterad 

 into the thick wall just dorsal to the middle ventricular groove. 

 Indeed the proliferation and st reaming of these cells is the active 

 cause for the thickening of this part of the wall and the forma- 

 tion of the middle ventricular groove. Further thickening of 

 this part of the wall deepens this groove and produces the dor- 

 sal ventricular groove at the point indicated in figure 9. 



In figures 9 to 12 appear important relations of the dorsal 

 border of the olfactory area to the pallium. Here it is quite 



