186 G. ELLIOT SMITH. 
physis (pit.), which extends forwards for a considerable dis- 
tance. It consists of a dense mass of highly convoluted 
tubules (fig. 11, pié.), lined with cubical epithelium. Imme- 
diately in front of the optic chiasma the floor again becomes 
depressed (fig. 2, 7. 0.), and on either side of the middle line 
forms a distinct recess (fig. 11, 7. 0.). A comparison with the 
early stage of the Perameles brain shows that this recess is 
the remains of the optic diverticulum, and therefore cor- 
responds to His’s recessus opticus (preopticus—Burck- 
hardt). According to His, the recessus opticus corresponds 
to the anterior extremity of the limiting furrow (Grenz- 
furche) between his alar (Fligelplatte) and basal (Grund- 
platte) laminze, to which Reichert has given the name “ sulcus 
Monroi,” without, however, recognising its important mor- 
phological significance. 
Immediately in front of the recessus opticus the median 
wall takes a sudden bend into the vertical direction, and at the 
same time becomes enormously thickened to form a large mass 
rhomboidal in section (fig. 2, 2. inf.), which His calls the 
“lamina terminalis” and Burckhardt the “lamina 
infra-neuroporica.” According to His it is formed by the 
meeting and fusion in the middle line of his Fliigelplatten, 
but according to v. Kupffer and Burckhardt it forms part of 
the floor (Bodenplatte). The researches of His seem to 
indicate clearly enough that it corresponds to part of the frontal 
suture (Schlussnaht), but more convincing evidence is required 
before it can be granted that it is formed purely from the 
Fligel-, aud not also from the Grund-, platte. This question 
will be again referred to later on. In the dorsal part of the 
lamina infra-neuroporica a large rounded mass of fibres will be 
seen (a. c.) near the posterior surface. This is the anterior 
commissure. In all Vertebrates this phylogenetically very 
ancient and primitive connecting link between the two hemi- 
spheres crosses the middle line in the same position in the 
lamina infra-neuroporica, so that it forms an easily recognisable 
basis for comparing the perplexing regions which surround it, 
Immediately in front and above it there is a small scattered 
