221 



and tlie septum at the same place as where in Monopterns the 

 sulcus cuts deep into the hemispheres. From this it is evident that 

 the sulcus limitans telencephali is present at first in Sjnbranchus 

 in the same form as in Monopterns, but that later it grows together 

 in a similar waj as in the posterior portion of the central canal 

 of the spinal cord, where only a septum ependymale remains. 

 In consequence of this the sulcus is only indicated bj a very faint 

 groove in Synbranchus. 



In Cyprinus, where Sheldon has described this groove, the sulcus 

 limitans runs entirely on the median side of the hemispheres and 

 only at its caudal end does it reach the dorsal surface of the fore- 

 brain then lying on the dorso- median side of the hemispheres. In 

 most of. the specimens of Teleosts, which I examined as to this, 

 the groove is found at the same place as in the carp. But in the 

 Synbranchidae the course of the sulcus limitans is entirel}' modified 

 owing to the enormous development of the septum. This body, in 

 most Teleosts, covers the entire median wall of the hemispheres 

 ventrally from the sulcus limitans. Whereas it is comparatively 

 small at the front of the fore-brain there covering only the ventral 

 half of the median wall of the cerebrum, it grows out caudally 

 in a dorsal direction and finally covers the whole median side of 

 the hemispheres. 



In Monopterns the frontal end of the sulcus limitans lies at the 

 same place as in other Teleosts, about half way up the median 

 wall of the hemispheres. From here this groove runs slightl}' 

 caudally, but then makes a sharp bend and further proceeds in a 

 dorso-frontal direction to the upper surface of the brain (fig. 2). 

 Here the groove curves gradually in a caudal direction and then 

 runs backwards almost parallel to the median line. (Fig. 1). 



This course of the sulcus limitans is, as has been said, caused 

 by the enormous increase of the septum. As in Cyprinus the frontal 

 termination of this body occupies only the ventral half of the median 

 side of the hemispheres. But the greater part of it has developed 

 strongly in a dorsal direction. The whole median side of the 

 hemispheres and a part of the dorsal side are covered by it. 

 Moreover it protrudes there somewhat in a frontal direction covering 

 the striatum, in consequence of which the sulcus limitans is bent 

 here in a dorso-frontal direction (fig. 2). This dorsal growth also 

 explains why the sulcus limitans cuts so extremely deep into the 

 fore-brain. This groove also proceeds over the posterior side of the 

 cerebrum and forms there, caudally from the epistriatum, the boundary 

 between the septum and the tuberculum posterius. 



