100 MARION HINES 
than in the stage previously described. ‘On the medial wall, 
the hippocampus does not bulge into the hemisphere except pos- 
terior to the region of the tela chorioidea telencephali medii. 
However the sulcus limitans hippocampi lying ventral: to the 
hippocampus extends from the tip of the temporal pole over the 
foramen and becomes lost just caudal to the olfactory bulb 
evagination. The original caudal pocket of the ventricle has 
swung ventro-anteriorly and carried with it the lateral complex 
of the nucleus caudatus. The neopallial arch which bridges the 
lateral division of the corpus striatum and the medial olfactory 
area is much higher than before. The plexus chorioideus ven- 
triculi lateralis almost fills the cavity. The chorioidal fissure is 
filled with mesenchyme and blood vessels. 
The outer contour of the telencephalon begins to resemble 
that of the adult. In the center of the lateral surface an area of 
retarded growth is present, the future island of Reil. Dorsal, 
caudal, caudo-ventral, and rostral to this point of slow growth, 
the telencephalon swings out, growing as it were between its 
points of attachment to the diencephalon. Upon the medial 
surface the line of separation of the cerebral hemisphere from the 
evaginating olfactory bulb is carried up on the wall as a small 
indentation, which terminates rostral to the lamina terminalis. 
This is the fissura prima of His. Caudal to the velumtransversum 
the fissura hippocampi can be traced to the tip of the temporal 
pole. Rostral to this point this fissura no longer can be identified 
on the medial surface of the hemisphere. The changes which 
have taken place in growth between the two embryos H 41 
(32.1 mm.) and‘H 163 (39.1 mm.) are as follows: 
1. Marked evagination of the olfactory bulb, which accentuates 
the fissura prima of His. 
2. Great growth of the lamina terminalis, together with a 
lateral extension of the septal region into the ventricle. 
3. The fissura hippocampi is restricted to the medial wall 
caudal to the velum transversum. 
4. Constriction of the foramen Monroi by the growth of the 
midthalamic region. 
