102 Journal of Comparative Neurology 



at least passed for some distance into the substance of the thala- 

 mus (Fig. 31). On the contrary they pass slightly caudad and 

 give no evidence of extending into the cerebrum as he sug- 

 gests. 



The remaining structures of the diencephal have been 

 carefully described by Herrick (43), and the description here 

 given only confirms his observations, differing from them only in 

 a few minor points. Cephalad and mesad of the supracom- 

 missural tracts is found the nidus of the habena consisting of 

 thickly clustered cells. The caudal portion of this nidus is 

 shown in Fig. 3 1. Cephalad and slightly ventrad of it lies another 

 nidus, in which the cells are less closely packed. This is Mey- 

 nert's nidus and from it the fibers of Meynert's bundle originate 

 and extending caudo-ventrad end in the floor of the cephalic 

 portion of the mesoccele in close relation with the oculo-motor 

 nidus (Fig. 36). This fiber bundle in the turtle is diffuse and 

 does not show so plainly as the corresponding tract in the Am- 

 phibia. Directly ventrad of the nidus of the habena lies a large 

 dense nidus, nearly globular in form, that is the most conspic- 

 uous object in the sections of this region (Fig. 31). Its struc-' 

 ture consists of a very dense ground work or stroma that is 

 pierced by a great number of blood vessels. In this stroma are 

 imbedded scattered cells. To this has been given the name of 

 nidus centralis. From its ventro-mesal portion fibers are given 

 off that extend ventro-cephalad (Fig. 31). Laterad of the nidus 

 are found the small geniculata into which optic fibers penetrate. 

 In the turtles the geniculata are not well developed or differen- 

 iated from the surrounding tissues. Fig. 3 1 shows a section of 

 the extreme caudal part of this structure. Ventrad of the 

 nidus centralis lying near the meson is another nidus that con- 

 sists of cells thickly clustered together. This is, I believe, the 

 " nidus sub-thalamicus " of Herrick. From its lateral margin 

 fibers are given off that join with the bundle from the nidus 

 centralis (Fig. 31). Caudad of these structures is another 

 nidus lying ventrad of Meynert's bundle (Fig. 36) to which the 

 name ruber was given, following the interpretation of Herrick. 



Large cells extend from the region of the nidus subthala- 



