Herrick, Brain of Ccftain Reptiles. 129 



optic tract. The ganglion habenulae and the gray matter of the 

 tuber are distinguished and, in addition, a frontal and caudal 

 ganglion or, as he elsewhere terms them, nucleus anterior and 

 posterior occupying the median and lateral aspects of the thala- 

 mus. These masses constitute the subthalamus and ruber of 

 our papers. We have been able to locate several other niduli 

 and especially the homologues of the mammillaria just caudad 

 of the infundibulum. 



Where the thalamus adjoins the cerebrum the gray matter 

 is not segregated from the ventricular layer. The peduncles 

 pass into the striata in which are numerous scattered cells in a 

 dense stroma. (Plate XVI. Fig. 2.) In the midst of this gray 

 matter surrounding the preoptic recess of the third ventricle a 

 nidulus of larger cells — the pieoptic nididus which lies a short 

 distance caudad of the precommissure and extends from about 

 the level of that commissure to a point well ventrad. The large 

 fibres from these cells arch latero-ventrad and do not collect into 

 a definite tract. It seems most probable that they form a part 

 of the optic or infra-commissural system. Farther dorsad there 

 is a gap in the gray matter about the ventricle in which the for- 

 nix tracts lie. Dorsad of this region is a clustre of similar cells 

 which lie in the cephalo-caudal plane and give off processes 

 which may be traced in the clear space enclosing the descend- 

 ing fornix tracts. These cells seem to be intercalated in the 

 tracts. In longitudinal sections (Plate XVII. Figs. 2, 3.) a 

 clear space containing fibres from the preoptic nidulus separates 

 the gray matter of the preoptic recess into a cephalic and 

 candal portion //r. 0. c. i and pre. 0. c. 2. 



A transection somewhat caudad of the region just described 

 reveals the fact that the gray matter has considerable gained in 

 complexity. The habena lies dorsad and beneath it a strong 

 stratified nidulus which may be vaguely compared with the sub- 

 thalamicus of fishes. Immediately ectad and rather dorsad of 

 this group is what may be confidently homologized with the ex- 

 ternal geniculatum of fishes and, strangely enough, it shares 

 with the latter group the striking peculiarity of having a pseudo- 



