328 JoiTRNAi. OF Comparative Neurology. 



fin; /, //, ///, /I'., nerves to the four gills, respectively; n. .«/., the 

 first spinal nerves. 



For full discussion of these nerves see text under cranial verves. 



Fig. (). Transection of cerebrum of Ictahirns cephalad of the 

 anterior commissure. 



Fig. 7. Transection of the same brain at the level of the prx- 

 commissura, Free. The tracts from the olfactory radices are seen in 

 section dorsad of the prjecommissura on either side the median line. 

 O. fr., optic tracts; Fed., peduncular fibres. 



Fig. 8. Transection of the same brain at the level of the habena, 

 H.; Cer., cerebellum. 



II.— STUDIES ON THE BRAINS OF SOME AMERICAN 

 FRESH-WATER FISHES. 



C. L. Herrick. 



A. — Topography. 



The olfactory lobes have an essentially similar structure 

 throughout the various families of Teleosts, but there is 

 a great variation in position, which is a function of the 

 position of the nasal capsules and the form of the cranial 

 cavity. 



Every gradation between an olfactory lobe closely sol- 

 dered to the cerebrum and one separated by many times the 

 length of the whole brain from the hemispheres may be en- 

 encountered in our fresh-water fishes. The gizzard-shad 

 {Dorosoma) ., which has a decidedly reptilian brain, is an 

 illustration of the first type (Figs. 6-7, Plate XIX). Sec- 

 tions of the olfactories of this species in front of the cerebrum 

 are semi-oval, with the larger extremity of the oval dorsad. 

 A shallow groove occupies the middle of the dorsal surface. 

 In section, the membranes may tend to separate from the 

 lobe, but there is no true ventricle. At this level the lobe is 

 composed of the usual glomerulary structure with Deiter's 

 nuclei, and the whole is richly supplied with small vessels. 



