Herrick, Brain of Certain Reptiles. 95 



in snakes, as in all other groups, of a sharply restricted conspic- 

 uous nidulus perched upon the summit of the diencephalon and 

 ■bounded caudad by the supracommissure. It is double, being 

 continued on either side some distance beneath the plexus to- 

 ward the cerebrum. The outline of a longitudinal section is tri- 

 angular with the acute projection cephalad. The area thus 

 marked off is enclosed by a close series of deeply staining cells 

 and the interior is frequently filled with concentric or irregular 

 rows of similar cells. This structure is found in a similar devel- 

 opment in fishes. 



The supracommissure penetrates the caudo-lateral part of 

 the nidulus and passes along the cephalo-lateral border of the 

 diencephalon, diverging to surround the ventral peduncles later- 

 ad and entering the sinus which separates the pyriform tuber- 

 osity from the postrhinal. A second part of the supra-commis- 

 sure of authors, which we have elsewhere called the commissura 

 habenaria, breaks up into numerous small bundles within the 

 habena. 



Laterad of the habena is a rather distinct nidulus ( nidulus 

 Meynerti ) which is the origin of the Meynet's bundle. The 

 cells of this nidulus are more scattered as wjU as smaller and 

 are irreglarly arranged in a stroma of crossing fibres. A third 

 nidulus is immediately ventrad of the habena and is enormously 

 developed in turtles. It is larger even in snakes than the others 

 and lies cephalo-dorsad and mesad of the ruber. It may be 

 called the nidulus infrahabcnaria. In structure it resembles nid- 

 ulus Meynerti but may have a concentric wall of cells like the 

 habena.. From the cephalic aspect of the habena the taenia 

 thalami extends to the cerebrum (?) From the caudo-ventral 

 aspect of the nidulus Meynerti the Meynert's bundle passes 

 almost directly caudo-ventrad to the inerpuduncular, while the 

 tract of the supracommissure lies upon the cephalo-lateral aspect 

 of the nidulus. The infrahabenary nidulus, in a section reveal- 

 ing these relations, lies mesad of the nidulus Meynerti and cau- 

 dad of the cephalic part of the habena. For corresponding re- 

 lations in fishes compare Plate VII, Figs. 6-9, and Plate VIII, 



