Kappers, Teleostean and Selachian Brain. 21 



epiphysis cerebri, which passes over by means of a thin roof plate 

 into the region of the commissura posterior. This roof plate, 

 which is for only a small part nervous, is in front somewhat over- 

 lapped by the back part of the lobi anteriores, and latero-dorso- 

 caudally by the roof of the mid-brain, the tectum opticum, which 

 is so strongly developed in fishes and especially the bony fishes. 



The highly developed tractus opticus, which has already 

 decussated, extends ventro-laterally along almost the entire length 

 of the walls of the 'tween-brain (Figs, xxvi, xxvii, xxviii, Plate II). 

 The ventral wall with its excrescences, the lobi inferiores, extends 

 a great deal farther backward, as appears in Figs, xxix to xxxiii, 

 which show these excrescences still present under the mid-brain 

 at the level of the oculomotorius and trochlears. This enormous 

 development of the thalamus base, or hypothalamus, is to be 

 attributed to the numerous tracts and nuclei situated within it, 

 among which there are some in the back part of the lobi inferiores 

 which are probably to be considered as homologous with nuclei 

 of the mid-brain of the higher vertebrates. 



Now, proceeding \o the description of these tracts and nuclei, I 

 shall demonstrate them from preparations of Gadus morrhua 

 {cf. Figs. 4 and 5, on Plates XI and XII). 



In the first place I shall take up that part of the thalamus 

 which immediately follows the fore-brain, the prcsthalamus of 

 C. L. Herrick. Before describing the attachments between the 

 fore-brain and the parts caudad of it I must mention a flat, high, 

 medially situated nucleus of large cells found in Lophius (Fig. 

 xxvi) and Gadus (Fig. xxxiv), which was known to Mayser and 

 Van Gehuchten, but extensively treated and figured by C. L. 

 Herrick as the nucleus prceopticus, a name which I propose to 

 retain. As it is exactly at the border of the fore-brain and 'tween- 

 brain, it was called nucleus posterior of the fore-brain (thalamic 

 part) by Haller who, as well as Mayser, was of the opinion that 

 some optic fibers ended there. C. L. Herrick describes its cells 

 as very large, which agrees with what I found. Further, he men- 

 tions that probably the nucleus forms one whole with a similar 

 post-optic nucleus and that from there some fibers originate going 

 latero-ventrally; but then he says, "The function and nature of 

 these highly specialized cells is unknown." These cells have 

 likewise been described for the ganoids, both by Goronowitsch, 

 who gives several pictures of them, and by Johnston who 



