THE FISSURA HIPPOCAMPI 87 
(ventro-medial sector of the hemisphere, p. 107) and resembles 
in form and morphology the septum ependymale of the amphibian 
brain (fig. 14, Sept. epen.). Almost the whole of this portion 
ultimately is thickened by intrinsic differentiation of neuro- 
blasts. 
The portion of the area epithelialis lying above the angulus 
terminalis is permanently membranous. Its ventral border is 
continuous with the septum ependymale, from which at this 
age it is not structurally distinguishable. Medially it is bounded 
by the area chorioidea of the telencephalon medium, and dorsally 
and laterally by the sulcus limitans hippocampi and primordial 
TABLE 3 
Telencephalic structures in and near the midplane 
MIDPLANE STRUCTURES OF THE TELENCEPHALON CONTIGUOUS AREAS OF THE CEREBRAL 
MEDIUM HEMISPHERE 
Recessus preopticus Septum 
Lamina terminalis 
Pars crassa Septum 
Area epithelialis 
Pars tenuis Septum ependymale 
Angulus terminalis 
Area chorioidea 
Tela chorioidea telencephali medii Area intercalata 
Paraphyseal arch Lamina epithelialis 
Velum transversum Lamina epithelialis 
hippocampus. It extends backward beyond the velum trans- 
versum toward the occipital part of the hemisphere (figs. 12 and 
14, A. ep.), and in later stages it follows the ventral border of 
the hippocampal formation as far as the tip of the temporal 
lobe (figs. 17, 18, 20). 
In the light of future differentiation, the entire area epithelialis 
may be further subdivided into: 1) the septum ependymale, 
already referred to; 2) the area intercalata (fig. 14, A. int.) lying 
contiguous with the tela chorioidea telencephali medii (fig. 14, 
Tel. ch. tel. med.) within which choroid plexus is never developed; 
3) the lamina epithelialis (Lam. ep.) lying opposite to the para- 
physeal arch and the di-telencephalic junction and in later stages 
