340 ELIZABETH CAROLINE CROSBY 
Nucleus preopticus (figs. 9, 10, 18 to 21). This term has been 
applied to the cell mass which appears in the region of the pre- 
optic recess just in front of the level of the commissures and which 
extends caudad still occupying this position. It passes over 
into the hypothalamic region with no definite line of separation 
between the two areas. The nucleus preopticus receives im- 
pulses from the stria terminalis, from fibers of the medial olfac- 
tory tract which have decussated by way of the anterior com- 
missure, and, at its anterior end, from some few fibers of the 
tract of the diagonal band of Broca. 
Interstitial nucleus (figs. 10, 19, 20). Cajal (11, vol. 2; p. 
723) described this nucleus and figured it in the mouse, calling 
it ‘“‘noyau interstiel de la voie de projection de |’écorce tempo- 
rale.’ He says further ‘‘Malheureusement, il ne nous a pas 
été possible de déterminer de facon précise les relations qui 
existent éntre la bandelette semi-circulare et ce noyau, et cela 
& cause de la rareté des bonnes imprégnations. Ajoutans que 
cet amas de la région sousthalamique pourrait fort bien étre 
encore un ganglion moteur.” 
Johnston (’15) has described the olfactory projection tract 
of Cajal for the turtle but has said nothing of the interstitial 
nucleus. In the alligator the nucleus appears in the preoptic 
region near the posterior end of the hemisphere as a ridge of 
cells extending lateralward in close relation with the nucleus 
ventro-medialis, arching dorso-medialward above the forebrain 
bundles and extending medialward into relation with the more 
dorsal part of the mass of the preoptic nucleus. It extends 
caudad throughout the preoptic region but in the hypothalamic 
region is gradually replaced by the hypothalamic nuclear ridge. 
Part of the fibers of the olfactory projection tract of Cajal 
arise from the ventro-medial nucleus. Cajal (11, vol. 2, p. 
725, fig. 463) has shown some of the neurones of that nucleus 
giving rise to these fibers. Many of the fibers having such an 
origin quite probably send off collaterals among the cells of the 
interstitial nucleus. Part of the fibers of this olfactory projec- 
tion tract arises from the interstitial nucleus. The tract passes 
caudad with the fornix into the ventral part of the hypothalamus. 
