Hekrick, MorpJioIogy of Brain of Bony Fishes. 213 



length of cerebrum, 6 mm.; width of cerebrum, 7.:; mm.; 

 width of optic lobes, 10 mm.; width of cerebellum, 11.25 

 mm.; length of cerebellum in the median median line, 8.5 

 mm. 



Cranial Nerves. — Compared with the size of the brain, the 

 cranial nerves are enormous, much larger than in any other 

 fish which has come to our notice. This is a function, doubt- 

 less, of the enormous size of the head in the cat fishes. The 

 olfactory nerves are very short, passing directly from the 

 olfactory lobes into the nasal cavities in numerous separate 

 bundles. The optic nerves are long, passing out; in large 

 fish , for several centimetres parallel to the olfactory crura, then 

 diverging at at acute angle to the orbits. They arise from the 

 ventral surface of the thalamus, immediately cephalad of the 

 hypoaria, are quite distinct from each other at the origin and 

 remain so throughout, crossing, however, below the cere- 

 brum. They are not, at first, cylindrical, but very strongly 

 flattened dorso-ventrally. The other cranial nerves may be 

 conveniently divided, after Gegenbaur, into two groups, the 

 trigeminus group and the vagus group. In both of these 

 groups the relations are greatly complicated, not only by the 

 large size of some of the nerve roots, but by the presence of 

 plexi. Only the more important of these are noted, and in 

 the peripheral distribution many of the smaller branches are 

 omitted. 



In the trigeminus group the fifth is of supreme import- 

 ance, and absorbs many of the others. The third arises as 

 a single strand under the caudo-lateral angle of the hypoaria, 

 passes into the fifth and loses its identity completely (Plate 

 XVII, Fig. 4, III). The fourth is minute. It arises from the 

 caudal end of the optic lobe and also passes out with the 

 fifth. The fifth is larger than all of the other cranial nerves 

 combined, and passes out of the cranial cavity by no less than 

 four distinct foramina. These are indicated in approximately 

 their relative positions in Plate XVII, Fig. ^. For convenience 

 of description the various branches of the fifth will be 



