Heruick, Morphology of Brain of Bony Bls/ics. 241 



diverticle, the lumen of which has been extinguished by the 

 same ventrad pressure, so that the dorsal and ventral granular 

 layers adhere and fuse in the centre. Some evidence of the 

 cavity still remains, however, in spurious lateral recesses, 

 consisting only of membrane connecting the partially everted 

 lateral portions of this ventricular layer. The posterior por- 

 tion of the cerebellum is thus reduced to a double leaf-like 

 valve over the calamus region. 



In Cyprinoid fishes the cerebellum is greatly developed, 

 but strictly the same principle is followed as indicated above. 

 The volvula is highly developed and complicated. The con- 

 nection between the dorsal lamina of the volvula and the 

 caudo-lateral edges of the optic tectum is affected well ceph- 

 alad near the median line between the tori longitudinalis. 

 Behind the valve there is a sudden dorsal expansion contain- 

 ing a moderate cephalad protrusion of the cerebellar ven- 

 tricle, which latter is connected by a dorsally elongated strait 

 with the fourth ventricle. The posterior part of the cere- 

 bellum is free and directed obliquely dorso-caudad, and is 

 flattened somewhat. The caudad protrusion of the ventricle 

 thus becomes a mere line or is indicated only by the fused 

 granular zones of the dorsal snd ventral lamina. The lateral 

 lobes of the cerebellum are very large. 



In the buffalo-fish, Carfiodcs, the cerebellum has a strong 

 but not exaggerated development. The optic lobes, in con- 

 sequence, are thrust cephalad and moderately dilated. The 

 volvula is enormously developed and thrust forward. Its 

 most remarkable peculiarity is that cephalad it becomes 

 bifurcate. The dorsal lamina is fused with the ventral for 

 much of its length, and the granular portion of the dorsal 

 lamina is present only near the tip. The lamina becomes free 

 caudad and unites with the velum near the median line, as in 

 the carp, though the union does not take place so far within 

 the optic lobes and the tori extend far out on the velum. 



In the region of the valve the lower lamina is greatly 

 thickened. Except that the cephalad diverticle of the cere- 



