J. B. JOHNSTON 
REFERENCE LETTERS - 
b.o., bulbus olfactorius, formatio bul- 
baris. 
c. a., commissura anterior 
ch., chiasma opticum. 
c.hipp., commissura hippocampi. 
c.p., commissura posterior. 
c.p.a., commissura pallii anterior. 
C.p.p., commissura pallii posterior. 
c.sup., commissura superior (Osborn). 
dienc., diencephalon. 
di-tel., di-telencephalic boundary. 
d.p., decussatio postoptica. 
e., epiphysis. 
em.th., eminentia thalami. 
fi., foramen interventriculare. 
f.olf., fila olfactoria. 
f.p.p., fibers from the parapineal body. 
g., olfactory glomeruli. 
hem., hemisphere. 
hy., hypophysis. 
hyp., hypothalamus. 
l.o., lobus olfactorius (secondary cen- 
ters). 
l.s., lamina supraneuroporica. 
l.t., lamina terminalis. 
l.v., lateral ventricle. 
m., caudal margin of lamina supraneu- 
roporica. 
mesenc., mesencephalon. 
n.h., nucleus habenulae. 
n.olf., nervus olfactorius. 
nuc.olf.med., nucleus olfactorius medi- 
alis. 
par., paraphysis. 
p.c.b., precommissural body. 
p.h., primordium hippocampi. 
p.p., parapineal body. 
pt., pretectal region. 
rec.ph., recessus praehabenularis. 
r.m., recessus mammillaris. 
r. n.,recessus neuroporicus. 
r.p., recessus praeopticus. 
r.po., recessus postopticus. 
s.d., saceus dorsalis. 
s.l., suleus limitans hippocampi. 
s.l.H., suleus limitans of His. 
s.m., stria medullaris. 
s.m.1, first bundle of stria medullaris 
s.med., sulcus diencephalicus medius of 
Herrick. 
s.hy., sulcus hypothalamicus. 
sub.hab., subhabenular region. 
t.c., tela chorioidea. 
tel.m., telencephalon medium. 
t.f., taenia fornicis. 
thal., thalamus. 
t.p., tuberculum posterius. 
tr.c-h., tractus cortico-habenularis. 
ir.h-p., tractus habenulo-peduncularis. 
tr.o-h., tractus olfacto-habenularis. 
ir.op., tractus opticus. 
tr. pall.,tractus pallii. 
v. tr., velum transversum. 
Fig. 1 The medial surface of the right half of the brain of Mustelus to show 
the position of the velum transversum in selachians. 
eminentia thalami which is not lettered. 
Medial view of the right half of the telencephalon and diencephalon of 
The olfactory bulb is not drawn. 
Fig. 2 
an adult Acipenser. 
It is attached to a slight 
The velum transversum is 
a very deep fold of the tela chorioidea which is nearly horizontal in position. It 
is attached to the eminentia thalami as in selachinas, amphibians and others. 
