334 ELIZABETH CAROLINE CROSBY 
absolutely clear) found in the olfactory bulb of the alligator 
illustrate this condition, for they lie in the granule cell layer— 
the position of the primitive central gray—yet aid in the for- 
mation of the glomeruli and send their axones into the tractus 
olfactorius. Sheldon (’12) has shown a similar condition in his 
description of certain stellate and goblet cells in the olfactory 
bulb of teleosts. 
Other stellate cells and many of the larger goblet cells of the 
reptilian granule cell layer have lost their connection with the 
fila olfactoria and receive their impulses by way of the axones 
of the mitral cells. In turn, they send their axones through 
the tractus olfactorius and, from a functional standpoint, are 
secondary olfactory neurones. A similar state of affairs has 
been described by Sheldon (’12) for teleosts. 
A smaller number of small stellate cells and goblet cells have 
lost their connection with the tractus olfactorius and discharge 
into the plexiform layer, serving apparently the usual correlat- 
ing and summating function of granule cells. Are these the 
forerunners of the most highly specialized granule cells of higher 
forms? 
Olfactory crus 
The anterior continuation of three of the centers of the hem- 
isphere are to be found in the crus (fig. 14). These are the nu- 
cleus olfactorius anterior, the pyriform lobe complex, and the 
hippocampus. Mitral cells are found in the olfactory bulb 
back to the point where it passes over into the crus. There 
they are replaced on the lateral side by cells of the pyriform 
lobe complex and on the medial side by the anterior continua- 
tion of the hippocampus. In the anterior end of the crus, the 
granule cell layer is replaced by the cells of the nucleus olfac- 
torius anterior, which takes its characteristic ventro-medial posi- 
tion. The position, cell structure, and significance of these 
centers will be discussed immediately under the head of centers 
of the hemisphere. 
