Herrick, Morphology of Brain of Bony Fishes. 69 



torus longitudinalis to the tectum — fibres which must be distinguished from 

 the Sylvian commissure. , 



PLATE VI. 



The figures on this plate are in each case drawn in outline with 

 camera lucida, and all tracts and principal niduli are as outlined with the 

 camera. Only such details as occur in the single section are introduced, 

 except in the case of the dotted lines indicating in Fig. i the course of 

 the combined anterior peduncle of the cerebellum and tract of the com- 

 missura horizontalis which would appear in the section were it not slightly 

 oblique. 



Fig. I. Longitudinal section of the entire brain of Haploidonohis near 

 the median line. The tectum is not cut, as it lies laterad of the plane of 

 section. The parts are named upon the drawing. For the region of the 

 habena compare Fig. 4. The nidulus rotundus (or ruber) lies in close 

 juxtaposition to the nidulus subthalamiciis . The corpus geniculatum lies 

 well ventrad. The medullary part of the hypoarium with its three-fold 

 fibrous connections is here termed mdulus niger. 



Ftg. 2. A similar section somewhat laterad, passing through the 

 mammillare (Mam.) 



Fig. 3. A similar section farther laterad, illustrating especially the 

 concentric arrangement of the tectum fibres in passing through the col- 

 liculus. 



Fig. 4. A portion of a similar section through the habena, more 

 highly magnified. 



Figs. 5, 6. Two transverse sections through the mesencephalon of 

 very young specimens of Belone, the former at the nidulus ruder the latter at 

 the exit of the third nerve. 



PLATE VIL 



Fig. I. A portion of a transverse section of the tectum opticum of 

 Lucioperca. The section is from the middle of the left side. The epithelial 

 cells are rendered somewhat confused by reason of a slight obliquity and 

 the tearing due to cutting. Above the ental ganglion layer (2) the walls 

 collapse and the interspaces are filled with the stroma. For details see 

 text. 



