16 Edward F. Malone. 



is extreme, whereas in the cells of the nucleus tubero-mammillaris the 

 N"issl substance is not so densely packed together on the periphery and 

 more of it is present in the central portion of the cell. In other words 

 the Nissl substance in the cells of the nucleus tubero-mammillaris is 

 more diffusely distributed throughout the entire cell. The difference 

 in cell type obtains throughout the entire extent of both nuclei. A 

 study of the illustrations shows that while other differences in cell type 

 occur in certain animals the fundamental difference consists in the 

 mode of distribution of the Nissl substance (Figs. 38 and 41 ; 44 and 

 47; 50 and 52; 55 and 57). 



The separation of the basal optic ganglion from the nucleus paraven- 

 tricularis hypothalami on the basis of cell type is difficult. Fortunately 

 both are in all four animals sharply circumscribed, and although the 

 extremities of these two cell columns approach one another (Fig. 10), 

 they never actually fuse. A study of the location of these two cell 

 groups will show their axes are almost at right angles to each other. 

 In a former article I made the statement that the cells of the basal 

 optic ganglion in man could not be distinguished from those of the 

 nucleus paraventricularis, but a more careful study of the cell groups 

 in man together with their study in other animals proves that this 

 statement is not correct, although not far from the truth. As a matter 

 of fact I have been unable to observe any one fundamental difference 

 between these two types of cells which is clearly shown in all four 

 animal forms, although in each animal some differences are present 

 which always make a distinction possible. There is one difference which 

 holds fairly well for all forms, and this is the same difference that was 

 so evident between the cells of the basal optic ganglion and those of the 

 nucleus tubero-mammillaris, namely, the Xissl substance is more 

 densely massed on the periphery of the cell in the case of the basal optic 

 ganglion, while in the cells of the nucleus paraventricularis the Nissl 

 substance is more uniformly distributed throughout the cell. In man 

 ( Figs. 38 and 43 ) this difference is not marked, but in the basal optic 

 ganglion (Fig. 38) the Xissl substance on the ]3eriphery forms in part 

 large, irregularly placed masses of granules, while in the cells of the 

 nucleus paraventricularis (Fig. 43) the granules are smaller, more 

 uniform in size and do not stain so intensely; at the same time the 

 c-entral portion of the cell is somewhat more deeply stained (due to more 

 Nissl substance) than in the case of the cells of the basal optic ganglion. 

 Other differences in man are as follows: the cells of the basal optic 



