Herrick, Aloi-phologv of Brain of Bony Bis//cs. 339 



The fourth nerves pass caudad to the optic lobes, around 

 which they arch, and enter the narrow, slit-hke opening of 

 the volvula and then continue cephalad nearly to the level 

 of the caudal margin of the hypoaria, where they meet and 

 dip suddenly ventrad into the substance of the valve, then, 

 after decussating, they continue cephalad to the ventro- 

 lateral margin of the valve, and, arching about the aqueduct, 

 enter the nidulus near the median line and adjacent to the 

 aqueduct and bounded ventrad by the dorso-median fasciculus. 



Caudad of the valve the roof of the fourth ventricle 

 expands and thickens into the median lobe or vermiforme of 

 the cerebellum, being for sometime connected with the lateral 

 walls of the ventricle by thick lateral lobes which have not 

 the structure of the cerebellum, but contain an intimate 

 mixture of granules, nerve cells and fibres. The cerebellum 

 proper is, as above said, simply a caudad pouch 

 from the roof of the fourth ventricle, which, however, 

 remains for some distance in contact with a mass similar in 

 composition to the lateral lobes which forms the transition 

 into the velum posterior, and is homologous with the "bursa" 

 of the sturgeons. 



In the gizzard-shad, although the brain is so similar to the 

 moon-eye, externally, the cerebellum is remarkably modified 

 in details of structure. What at first gives great trouble, is 

 the fact that in the axial part of the cerebellum or vermiform 

 lobe the gray matter is apparently ectad instead of internal. 



To a point about one-third the length of the optic lobes 

 from their caudal boundary the relations are as above. The 

 volvula is small, and its cavity nearly closed. The cerebellum 

 proper is driven forward between the optic lobes, and 

 especially dorsad, so that, as though by actual lateral 

 pressure, the organ is thrust together upon itself and its 

 dorsal and cephalic surfaces are folded in along the median 

 line and the lateral white matter is reduced to a mere 

 membrane, only recognized by careful examination. The 

 appearance of lateral compression in the fungiform contours 



