88 MARION HINES 
extended backward beyond this junction accompanying the 
differentiation of the hippocampal formation in the temporal 
lobe (figs. 16, 18). The whole of the lamina epithelialis of these 
embryos becomes the lamina epithelialis of the adult lateral 
choroid plexus. The relations above described are expressed 
in the accompanying table 3. 
The morphological changes noted here in comparison with 
the 11.8-mm. embryo are as follows: 
1. The appearance of the pontile flexure and the lateral recess. 
2. The marked medial growth of the basal plates in the mesen- 
cephalon. 
3. Slight advance in the delimitation of hypothalamic struc- 
tures and more marked increase in the thalamic region lying 
between the sulcus limitans and the sulcus dorsalis. 
4, Change in the angle of the vault above the foramen in- 
terventriculare. 
5. Marked growth in the telencephalon, i.e., increase in size 
of the cerebral hemispheres, 1) by dorsal, caudal, and rostral 
growth, and, 2) by appearance of the corpus striatum as a ridge 
in the floor of the lateral ventricle. 
The 19.1-mm. embryo, University of Chicago, H 173 
(figs. 15 and 16) 
The whole of this brain was not modeled, but from the sections 
it is evident that the development of both the basal plate and 
the ganglia of the cord is precocious. The processes of develop- 
ment, already described in the medulla oblongata, have proceeded 
with a slight shifting of relative morphology only. The floor 
plate has maintained a progressive thickening. The depth of 
the lateral recess has increased. The primordium of the cere- 
bellum has appeared in the dorsal lip of the lateral recess. The 
midbrain has grown medially by a ventricular extension of the 
basal plate, while the roof plate and the alar plate have increased 
in thickness. 
In this embryo, as in the 14-mm., the changes in the contour 
of the thalamus and telencephalon are most marked. ‘The two 
ventricular markings, namely, the sulcus limitans and the dorsal 
