154 MARION HINES 
Levi's (04) description of the development of the fascia dentata 
in the rat, but his interpretation requires revision. 
The identification of the reptilian dorso-medial cortex with the 
fascia dentata of Meyer and Levi has been questioned by Cajal 
(11) and by Elliot Smith (10), who believes, however, that 
it is undergoing differentiation toward fascia dentata, a view 
supported also by Crosby (17) and in a modified form by John- 
ston (13, p. 391, and 715, p. 419). 
By what criterion hail the fascia dentata be eae 
connections, intrinsic chromatin staining, position, or history? 
To determine nerve connections in this material is impossible. 
The primordial fascia dentata shows the characteristic intensive 
nuclear staining even in its earliest stages of development. But 
its morphological disposition can be so followed from stage to 
stage up to the adult form that there is no doubt as to its identity. 
In vertebrates below the lowest mammals there is no represen- 
tative of this structure. Levi (04) has pictured the dorso- 
medial cortex of reptiles as containing a cortical lamination of 
deeply staining cells, whose connections according to Smith and 
Cajal are those of the hippocampus. Its boundaries have noth- 
ing in common with those of the mammalian fascia dentata. But 
knowing the origin of this tissue in human development, we 
naturally turn to the homologous region in the lower vertebrates. 
Such an area in both reptiles and mammals is the undifferentiated 
primordium hippocampi in the region of the developing fornix 
fibers. If the fascia dentata is a center for cortical reenforce- 
ment, as Cajal (11) thinks the neurone connections indicate, 
and not the main receiving station for incoming impulses over 
the medial olfactory tracts, as Elliot Smith (96) maintains, 
then it would seem natural for its development to be in abeyance 
in lower vertebrates. But if the reverse be true, we are at a loss 
to supply a reason for its undifferentiated condition in lower 
forms. It seems logical that it may develop from the cells of 
the primordium hippocampi, opposite the sulcus limitans hippo- 
campi, and that the development will be delayed in accordance 
with Cajal’s hypothesis of its function, until cortical associational 
mechanisms are well elaborated. Be that as it may, its anatomi- 
