12 Edward F. M alone. 



the optic tract) is missing; consequently the ganglion consists of two 

 entirely separate parallel columns of cells. Fig. 27 represents a section 

 between the two cell columns. As in man and macacus the ganglia of 

 opposite sides are united by a very few cells; this union occurs just 

 caudal to the optic chiasm (slightly caudal to the level represented 

 in Fig. 27). 



CAT. 



The basal optic ganglion in the cat (Figs. 31 to 35) has practically 

 the same location and extent as in the lemur. As in the lemur the gang- 

 lion consists of the same two parallel cell columns, which are completely 

 separate. Between Figs. 32 and 33 lies the region in which the gang- 

 lion is absent. Just caudal to the optic chiasm (caudal to level of Fig. 

 33) the ganglia of opposite sides are united in this series by a few 

 cells ; in the other two series of the cat no union was present. 



Comparing the location and extent of the basal optic ganglion in all 

 four animals the following facts should be noted: 



1. The basal optic ganglion in all four animals consists almost 

 exclusively (in some cases exclusively) of two compact, parallel cell 

 columns. The larger of these two columns lies superficially in the 

 anterior perforated substance along the line where this region becomes 

 continuous with the oro-lateral border of the optic tract ; the smaller 

 column lies superficially in the tuber cinereum along the line where it 

 joins the optic tract. 



2. These two constant, parallel cell columns are united in man, and 

 to a less extent also in macacus, by more or less diffusely scattered cells 

 of the same type which lie dorsal to the optic tract. 



3. In all four forms there occurs a union of the ganglia of opposite 

 sides by means of diffusely scattered cells located just caudal to the 

 optic chiasm. In man this union is very definite, in macacus less 

 definite, while in the other two animals it is rudimentary and due to the 

 presence of a very few widely scattered cells between the two ganglia. 

 In the cat even this feebly developed fusion is not present in all 

 individuals. 



4. Although the phylogenetic series from man to the cat is too short 

 to be of much service in revealing the phylogenetic development of so 

 constant a cell group as the basal optic ganglion, it is apparent that 

 as we descend the series the two parallel cell columns become separate 

 (more closely united in man than in macacus, and separate in the lemur 



