228 



in a ventral direction, and joins the rest of the tractus striothalamicus. 



The fore- brain of the Sjnbranchidae is remarkable, because it 

 forms, as it were, the final stage in the series of development of 

 the telencephalon of Ganoids and Teleosts. For, according to Sheldon, 

 the septum originally forms the ventro-median part of the fore-brain. 

 In Polypterus, which forms the first stage in this series of develop- 

 ment, this part still lies at its original place. The septum now 

 gradual!}' grows on the median side past the striatum, whereby the 

 striatal portion of the ventricle wall is more and more restricted. 

 This process going on, in some Teleosts the striatum disappears 

 altogether from the ventricular wall, and the sulcus limitans 

 telencephali forms the boundary between the septum and the dorsal 

 part of the cerebrum, the epistriatum. At the caudal end of the 

 fore-brain this process is further advanced than at the frontal end; 

 the sulcus limitans thus lying in front on the median side, at the 

 back on the dorso-median side of the hemispheres. 



Only in the Synbranchidae however, this process goes so far that 

 the septum reaches the dorsal surface of the cei-ebrum, whereby 

 the epistriatum is pushed aside and the sulcus limitans comes to lie 

 on the dorsal, or even dorso-lateral, surface of the hemispheres. 



The coalescence of the hemispheres may also be regarded as a 

 final stage in the development. In the Ganoids the two hemis- 

 pheres are far apart and the ventriculus medianus is broad. This 

 is also the case in primitive Teleosts, such as Salmo. In other 

 Teleosts the hemispheres approach each other more and more, and 

 in most Acanthopterygii jjiey lie right against each other; the 

 ventriculus medianus only being open in the ventral part above the 

 lamina terminalis and above the commissura anterior. In the 

 Synbranchidae the hemispheres, at least as regards their caudal lialf, 

 have almost entirely coalesced, and of the ventriculus medianus 

 only a narrow split remains, ven trail}' from this junction. 



LITERATURE CITED. 



1. Goldstein, Kurt. Untersuchungen über das Vorderhirn und Zwischenhirn 

 einiger Knochenfische. Arch, f mikr. Anat. u. Entw. Bd. 66. 1905. 



2. Horst, C. J. van der. Die motorischen Kerne und Bahnen in dem Gehirn 

 der Fische. etc. Tijdschrift d. Ned. Dierkundige Vereeniging. Bd. XVI. 1918. 



3. Kappers. G. U. Ariëns. The structure of the teleostean and selachian brain. 

 Journ. Gomp. Neur. Vol. 16 1906. 



4. Kappers, G. U. Ariëns- Die Furchen am Vorderhirn einiger Teleostier. 

 Anat. Anz. Bd. 40. 1911. 



5. Kappers, C. U Ariens und W. F. Theunissen. Die Phylogenese des Rhinence- 

 phalons, des Gorpus striatum und der Vorderhirncommissuren. Folia Neurobiologica. 

 Bd. I. Ifi08. 



6. Sheldon. R. E. The olfactory tracts and centers in Teleosts. Journ. Gomp 

 Neur. Vol. 22. 1912. 



