THE FISSURA HIPPOCAMPI ez: 
end, there is no change in these relationships. Anteriorly, how- 
ever, the cortical differentiation is comcident with the sulcus 
limitans hippocampi (fig. 49, Sul. vent.) and seems to be continu- 
ous with the same type of differentiation which lies dorsal to the 
root of the olfactory bulb. At both of these levels the septum 
contains three groups of cells as outlined in H 163 (39.1 mm.) 
and is separated from the hippocampus by the sulcus limitans 
hippocampi. There are no discernible paraphyseal pouch or 
postvelar tubules. 
Development in these two embryos may be summarized as 
follows: 
1. Cortical differentiation in the region of the hippocampal 
formation, anterior to the paraphyseal arch, and the coincident 
reduction in depth of the fissura hippocampi in this region. 
2. The great growth of the lamina terminalis in all directions 
and an intrinsic differentiation into three cell groups, the septal 
nuclei. 
3. The dorsal extension of the fascia dentata along the margin 
of the medial wall. 
4, The development of the anterior commissure and the fornix 
system. 
The eight brains described in the preceding pages have been 
arranged according to the time interval between the initiation of 
the growth process and its arrest, measured as the greatest length 
attained by the individual. The greater the difference in length 
the greater the growth changes. These embryos may be divided 
into the following groups: 
1. The 11.8-mm. 
2. The 14.0-mm. 
3. The 19.1-mm. and the 20.0-mm. 
4, The 27.8-mm. and the 32.1-mm. 
5. The 39.1-mm. and the 43.0-mm. 
This division is also a logical one, for when these groups are com- 
pared to the curve of change through which this particular 
protoplasm has passed, certain similarities are noticed, from which 
it seems that the recapitulation of phylogenetic processes is 
