114 MARION HINES 
which lies between the levels of the lamina terminalis and the 
velum transversum is an area transitional to the sickle-shaped 
postvelar tissue in which little or no cortical differentiation has 
taken place. It is in the latter that the fissure is best indicated. 
The fissure is best developed, then, in the least differentiated 
part of the hippocampus. ‘The fascia dentata (fig. 41, Fas. den.) 
is now a continuous band of clumped cells opposite the sulcus 
limitans hippocampi. ‘The fascia dentata is not coextensive with 
either this sulcus or with the hippocampal formation. However, 
the ventricular sulcus limitans hippocampi (Sul. vent.) seems 
to delimit its ventral extent except in that region where the an- 
lage of the hippocampus gradually fades into the olfactory 
bulb. 
The condition of the septum and septum ependymale is the 
same as that of H 91 (28.7 mm.), with the exception that its most 
dorsal portion is much wider measured antero-posteriorly. 
The growth changes may be summed as follows: 
1. More ventral differentiation of the preterminal portion of 
the hippocampal anlage with a coincident decrease in the depth 
of the fissura hippocampi, ventrally. 
2. Further thickening of the outer layer in the septum ependy- 
male. 
The 39.1-mm. embryo, University of Chicago, H 163 
(figs. 42 to 46) 
At the level of the tuberculum olfactorium (fig. 42, ef. fig. 18, 
tub. olf.) the vault of the hemisphere from the corpus striatum 
laterally to the sulcus limitans hippocampi medially presents 
the typical cortical differentiation. Following the tissue which 
lies immediately dorsal to the sulcus limitans hippocampi to the 
level of the lamina terminalis, the typical cortical layers do not 
extend as far ventrally as the sulcus. In the marginal velum 
opposite it lies the fascia dentata (fig. 43, Fas. den.). ‘This 
tissue is the most rostral limit of the hippocampus. ‘The area 
immediately ventral to the hippocampus is that of the septum. 
Its growth is very marked in all directions. That growth is 
largely the result of differentiation of a new diffuse nucleus. 
