112 MARION HINES 
ventralis, that area which in mammals is said to represent the 
whole lateral half of the hemisphere evagination, only two cellu- 
lar layers on the ventricular contour of the caudate nuclei and 
a diffuse cellular mass beneath them can be identified. Upon 
careful examination a thin layer of cells may be seen, swinging 
around the ventro-medial corner of the hemisphere in the marginal 
velum, the first evidence of the cortex of the tuberculum ol- 
factorium. ‘The relationship of tissue within the ventro-medial 
and ventro-lateral sectors is identical in the 19.1-mm. and 20- 
mm. embryos. 
This embryo shows an advance over the last in: 
1. The appearance of a clear zone in the septum ependy- 
male. 
2. Growth of neopallial tissue in the caudal and inferior aspect 
of the hemisphere. 
3. The hippocampal anlage begins to assume its definite 
shape caudally, i.e., the caudal end of the hippocampal forma- 
tion has advanced forward to define the temporal lobe (figs. 16 
and 17). 
4. The fascia dentata has differentiated as far as the temporal 
tip of hippocampal primordium. 
The 27.8-mm. embryo, University of Chicago, H 91 (figs. 38 and 39) 
The general relationships of the various components of the 
telencephalon are the same in this embryo as those described for 
the 20-mm. However, the intrinsic differentiation within the 
cortex has become evident. Within the neopallium two cell 
layers have migrated out of the matrix. The outermost layer 
is that of the pyramids (fig. 29, Pyr. c. l.), and one next the matrix 
is the intermediate cell layer (figs. 38, 39, Poly. c. 1.). But in 
the hippocampus the latter group only has appeared. The cells 
occupy the dorsal lip of the hippocampal fissure. This differen- 
tiation is especially marked anterior to the paraphyseal arch. 
Here also, as before, the primordial fascia dentata (figs: 38, and 
39, Fas. den.) lies opposite the sulcus limitans hippocampi (figs. 
38 and.39, Sul. vent.). 
