Johnston, The Brain of Petromyzon. 69 



the giant Mullerian cells of the mid brain be considered 

 as equivalent to Kolliker's nucleus of the posterior com- 

 missure, because according to Mayer they send their dendrites 

 through that commissure, requires no other comment than that 

 the true homologue of Kollikek's nucleus is present in Lampe- 

 tra. The commissura transversa is constituted, according to 

 Maver, of his Stabkranz and of the dendrites of cells of the tec- 

 tum. The latter are at least doubtful and I have (above)denicd the 

 existence of the Stabkranz in Petromyzon for the double reason 

 that I have found no such fibers and that in the absence of a true 

 cortex there can be no true Stabkranz; — and fibers running from 

 the hind brain, tectum, and hypothalamus to the olfactory area 

 are too anomalous to be considered. Mayer seems to have over- 

 looked the large tractus lobo-bulbaris which constitutes the post- 

 optic decussation Instead of this he describes the fibers from the 

 cellh in the cephalic part of the hypothalamus as running to the 

 striatum and olfactory area ("cortex"), partly crossed in the 

 anterior and infundibular commissures. These, too, are unlike 

 anything in the fish brain, and it would be difficult to state what 

 their function would be. His description of fibers from the 

 striatum to the hypothalamus and hind brain is due to confus- 

 ing the nucleus thaeniae with the striatum. Fibers from the 

 nucleus thaeniae do go to the hypothalamus. Fibers from the 

 striatum end for the most part, at least, in the thalamus ; I have 

 been unable to demonstrate any going to the hind brain. It is 

 not clear in the absence of figures, what MayiiR means by the 

 statement that there are no nerve cells other than mitral cells 

 in the olfactory lobe, — whether he considers all the cells as 

 mitral cells or denies the nervous nature of all except those 

 lying near the glomeruli. 



a. The olfactory lobe. 

 In the olfactory lobe of Acipenser the writer has described, 

 besides true mital cells, numerous slightly differentiated cells 

 which come into relation with olfactory fibers in the glomeruli and 

 send their neurites to the fore brain with those from the mitral 

 cells. These cells were interpreted as corresponding to the' 

 "kleine Pinselzellen"and granules of higher vertebrates and it was 



