20 'Joiiriial of Comparative Neurology and Psychology. 



the olfactory lobes. Surely most fibers of the commissura ante- 

 rior arise from the epistriatum and the striatum. Further investi- 

 gations are necessary to clear up this important question. 



In regard to the peripheral nerve fibers connected with the 

 fore-brain of the selachians, I should mention that I did not 

 succeed in finding the cerebral center of Locy's nerve, which 

 nerve Professor Johnston kindly demonstrated to me in some 

 selachians during my last stay in Naples, and which has been 

 regarded by Ernst de Vries as the analogue of the nervus 

 vomeronasalis in man. 



Chapter II. 

 'tween-brain, diencephalon or thalamencephalon. 



J. The 'Tiveen-hrain of the Teleosts. 



The 'tween-brain is considered to extend from the hind part of 

 the lobi anteriores, which have been described, to what is generally 

 called the tectum opticum, or more properly, to the commissure 

 which lies immediately before it, the so-called commissura 

 posterior, as the dorsal caudal limit, and ventrally to and including 

 the lobi inferiores, which lie much farther caudad. Accordingly, 

 the base of the 'tween-brain has a much greater fronto-caudal 

 extent than the roof. Besides this difference in length there is 

 another more important difference in the development of the 

 nervous mass, in that, while the base and lateral walls of the 

 'tween-brain are rich in tracts and nuclei, the roof is formed 

 almost exclusively of ependymal tissue folded in various ways. 



The fronto-caudal sequence of these evaginations and invagina- 

 tions in Lophius is as follows: First, there is an important invagi- 

 nation with many secondary inward projections, the plexus 

 choroideus of the third ventricle, from which originates in higher 

 vertebrates the choroidal plexus of the lateral ventricles of the 

 fore-brain. Then follows a part whose lateral walls extend higher 

 and whose roof also contains nervous elements called the epithala- 

 mus, consisting of the ganglia hahenulcB with their commissura 

 habenularis. (In this species neither paraphysis nor velum 

 transversum were clearly to be found.) Behind this part the 

 dorsal wall becomes thinner arid terminates in the foot of the 



