THE FISSURA HIPPOCAMPI 125 
of Warren and Bailey; it simply calls attention to a fact not 
recognized before, that the paraphyseal arch is present even in 
very young embryos in a simple form, extensive when compared 
to the whole midline, especially in these brains. It of necessity 
retains its fundamental importance as a midline structure. 
cE 
1 ah : e vent. qua 
5 | um pl ch en 4 v 
esr pl : 
Epey va - ; Oe Rec. preop. 
Dien. r-pl. 
. Kh : Lam.term. 
Vel. trans. tnt, 
Tel.r. pl. Tub. olf. 
fein OT Sat epen 
27” _ Prim. hip 
lan 
Undif. f.den. SS 
dul. vent. 
Fig. 8 This is a pen-and-ink outline of the same model as that shown in 
figure 7. Histologically distinct areas in the telencephalic medial wall are pro- 
jected in their relative positions upon its surface. The key to these areas as 
well as those of the other models will be found below the list of abbreviations 
(p. 121). The annotations on all of the models refer to numbers of specific sec- 
tions, whose photographs are reproduced in this paper or will appear in those 
which follow. 
If these midline structures prove to be the landmarks which 
the writer has shown them to be in the embryos so far studied (and 
certainly all the well-preserved embryos between the ages men- 
tioned which have been studied in the Department of Anatomy at 
Chicago and the Mall Collection in Baltimore substantiate that 
decision), the growth of the telencephalon adjoining them may 
be followed accurately. Herein lies an approach to data which 
