Xuclci Tiiberis Latcrales and the Ganglion Opticum Basale. 9 



changes have occurred : as the optic tract approaches the median plane 

 and applies itself to the base of the brain the cell mass continues to 

 increase in size, extending further laterally and also to a less extent 

 further medially, and assumes a position as a column on the dorsal 

 surface of the caudo-medial aspect of the optic tract, or in other words 

 it extends in the tuber cinereum along the line where the tuber joins 

 the optic tract. Midway between Figs. 6 and 7 the medial pole of the 

 column crosses the median line and caudal to the optic chiasm unites 

 with the corresponding column of the other side by means, however, of 

 only a few scattered cells situated in the iirfundibulum. The next 

 series (D) shows this fact. But still another change has occurred 

 between Figs. 6 and 7, namely, after reaching its greatest development, 

 which, as previously described, occurs at the juncture of the tuber 

 cinereum with the caudo-medial border of the optic tract, the cell mass 

 becomes rapidly diminished to- only a few scattered cells which are 

 situated on the dorsal (or deep) surface of the optic tract. Fig. 7 shows 

 the extent of the basal optic ganglion slightly oral to this region of its 

 poorest development; the section passes through the optic tract near 

 its oro-lateral border and since the section is near this border the cell 

 mass has increased in extent. Between Figs. 7 and 8 it increases 

 steadily in size to reach its maximum in Fig. 8 ; this figure represents 

 a section through the cell column which extends in the anterior perfor- 

 ated substance along the oro-lateral border of the optic tract. In Fig. 9 

 the basal optic ganglion has diminished in size, and this is due to a 

 shortening of the lateral portion of the column ; that the lateral portion 

 of the column should be shortened is evident when we recall that the 

 cell column lies parallel to the optic tract, and that the course of the 

 optic tract is such that in the present plane of section as one proceeds 

 orally the lateral portion of the tract appears and disappears first (see 

 Figs. 1 to 10). Fig. 10 shows the most oral portion of the basal optic 

 ganglion. The fact that the portion of the ganglion situated caudal 

 (medial) to the optic tract does not extend as far laterally -as that por- 

 tion situated oral (lateral) to the tract should be correlated with the 

 difference of the relation of the two borders of the tract to the base of 

 the brain ; for while the oral (lateral) border of the tract is in intimate 

 relation to the anterior perforated substance from the chiasm to a point 

 far lateral from the median plane, the caudal (medial) border of the 

 tract is in intimate relation to the tuber cinereum, which extends for 



