10 Edward F. M alone. 



a shorter distance laterally, and then the tract passes over the cms 

 cerebri, where of course it is no longer in relation to gray matter. 



To sum up. Series AC of man (Figs. 4 to 10) shows, in sections 

 almost parallel to the course- of the optic tract, the appearance of the 

 three parallel columns of cells which constitute the basal optic gang- 

 lion ; one column lies in the tuber cinereum along the medio-caudal 

 border of the optic tract, the second extends along the dorsal (deep) 

 surface of the tract and consists of only a few cells, while the third and 

 largest column extends in the anterior perforated substance along the 

 latero-oral border of the tract. The caudal column is continuous in the 

 infundibulum with the corresponding column of the opposite side. The 

 figures show the inevitable relation of three parallel columns in slightly 

 oblique section. 



Series D of man (Figs. 11 to 18) shows essentially the same relations, 

 but the plane of section is different. In the previous series the plane 

 was almost parallel to the course of the optic tract, although slightly 

 approaching the plane of a cross section ; in Series D the plane of sec- 

 tion is almost at right angles to the course of the optic tract, and both 

 the caudo-medial and the oro-lateral borders are shown in all sections. 

 It is evident that a plane of section at right angles to the median plane 

 (which would cut both halves of the brain symmetrically) could not 

 pass through the optic tract at right angles to its course, since the two 

 tracts converge towards the median plane as they pass orally ; therefore 

 to obtain a cross section of the right tract the plane of section must lie 

 more oral on this side than on the left. The asymmetry of the plane 

 of section of Series D is not quite great enough to produce a cross sec- 

 tion of the right optic tract, although this condition is very nearly 

 attained. 



When Fig. 11 of Series D is compared with Fig. 4 of Series AC the 

 location of the basal optic ganglion is rather confusing, for in the 

 latter series it appeared oaudally in the tuber cinereum near the medio- 

 caudal border of the optic tract, while in Fig. 11 it appears first in the 

 anterior perforated substance along the oro-lateral border; if we keep 

 in mind the asymmetry of the section, and the fact that the cell column 

 here shown extends further laterally than the other two columns of the 

 cell group and that in such asymmetrical sections the lateral portion is 

 the most oral, little difficulty should exist in realizing just why this 

 one of the three cell columns should appear first. Fig. 12 shows practi- 

 cally the game relations, except that the optic tract is nearer the median 



