272 Journal of Comparative Neurology. 



nidulus. The cells of this nidulus are very irregular in out- 

 line. They are neither typical pyramidal cells nor typical 

 flask cells. Probably they resemble the former more than 

 than they do the latter. In haematoxylin and in aluminium- 

 sulphate cochineal preparations, these cells are densely and 

 obscurely stained, and each one presents a densely stained 

 nucleus, within which is a densely stained nucleolus. 



The cmit/entia acustica is a slight projection into the 

 cavity of the fourth ventricle. This projection is situated 

 upon the floor of the fourth ventricle, about half way be- 

 tween the external root of the eighth nerve and the meson 

 (Plate XVIII, Fig. 11). This is a sub-elliptical body, and is 

 divided by a band of fibres into two unequal portions. That 

 division which lies nearest the ventricle is much larger than 

 the other portion. This eminentia contains nidulus B. 



Nidulus B (Plate XVIII, Fig. 18). — As has been men- 

 tioned above, this cell cluster constitutes the nervous portion 

 of the eminentia acustica. The band of fibres which divides 

 the eminentia into two unequal portions divides this nidulus 

 in a similar manner. In that section of this nidulus which is 

 nearest the fourth ventricle the nerve cells are crowded into 

 the mesal half, while the remainder of that portion of the 

 nidulus is filled with Deiter's corpuscles. In that section of 

 the nidulus which is on the other side of the band of fibres 

 the nerve cells are uniformly distributed. The cells of this 

 nidulus are small, gibbous, flask cells, which, in hcematoxylin 

 and in aluminium-sulphate cochineal preparations, are faintly 

 and obscurely stained, and each of which presents a faintly 

 stained nucleus, within which is a densely stained nucleolus. 

 This nidulus is surrounded on all sides by nerve fibres. 



It is quite probable that the two divisions of this nidulus 

 correspond to the two small and distinct but adjacent niduli 

 which occupy a similar position in the alligator brain.(') 



Nidulus T (Plate XVIII, Figs. 4, 11). — Mesad to the 



X Prof. C. L. Herrick, " Notes on the Brain of the Alligator," 1. cit., p. 153. 



