Johnston, The Brain of Petroniyzon. 67 



the thalamus and hypothalamus and ending in the glomerular 

 layer of the olfactory lobe ; fibers in the basal bundle from the 

 hypothalamus to the striatum proper ; the existence of the so- 

 called Stabkranz ; a resemblance between the cells of the hypo- 

 thalamus and those of the striatum ; the absence of cells from 

 the outer and middle layers of the tectum ; the formation of 

 the fasciculus longitudinalis posterior of fibers from the com- 

 missura posterior. The facts with regard to these points, as 

 they are understood by the present writer, are stated in the de- 

 scriptive part of, this paper. The following statements of Mayer 

 are also to be regarded as very doubtful in Petromyzon : that 

 the striatum sends fibers to the hind brain and hypothalamus; 

 that the vertical cells in the tectum send fibers to the hind brain 

 and the bipolar cells to the "cortex;" that the tectum sends 

 fibers to the posterior commissure. 



Some of these errors (as the writer must consider them) 

 are due to, or at least connected with, the misinterpretation of 

 the several parts of the fore brain. Mayer seems to have con- 

 fused the nucleus thaeniae with the striatum, either describing 

 the former nucleus alone as the striatum or including both in his 

 description. This accounts for the statement that the cells of 

 the hypothalamus resemble those of the striatum and that the 

 latter have central processes and dendrites which are always 

 directed backward. The cells of the nucleus thaeniae have 

 those characters, those of the striatum for the most part do not. 

 From his plate, however, it would appear that it is the ventral 

 part of the lateral expansion to which the name "Basalgan- 

 glion" is given. This is an error to the opposite extreme, since 

 the striatum does not extend far laterally in the so-called hemi- 

 sphere. The epistriatum seems to have been wholly overlooked 

 by Mayer. Ahlborn stated that the thalamus extends forward 

 to the anterior commissure at the cephalic limit of the lamina 

 terminalis. This is the olfactory commissure of the present 

 paper, and the thick dorsal portion of the wall of the fore brain 

 which Ahlborn thus included in the thalamus has been shown 

 above to be the epistriatum. Mayer seems to have completely 

 ignored this important and prominent body. I was at first in- 



