1908.|] Cell Lamination of Cerebral Cortex of the Lemur. 503 
Type“ R” Bess4, 
If the lips of the Sylvian fissure are opened out, it will be seen that. 
the anterior portion of both the superior and inferior walls form an 
operculum, and cover an area of cortex which is continuous with the 
cortex below the orbital sulcus anteriorly, and with that which lies directly 
above the rhinal fissure posteriorly. It is triangular in shape, the apex of 
the triangle being wedged between the walls of the Sylvian fissure about. 
half way between its posterior extremity and the vallecula Sylvu. This 
corresponds to the floor of the Sylvian pit in the human fcetal brain before 
the temporal and fronto-parietal opercula have covered it up to form the 
Sylvian fissure. It is bounded within the fissure both anteriorly and 
posteriorly by small sulci, which lie at the base of the superior and inferior 
walls respectively. Histological examination shows that this cortex is similar 
to, and continuous with, the type which borders the olfactory tract anteriorly, 
and the olfactory area posteriorly. When, in the higher apes, the develop- 
ment of the frontal lobe pushes the fronto-orbital sulcus downwards and 
backwards until its posterior extremity joins the Sylvian fissure (thus 
forming, according to Elliot Smith, the anterior ramus of the complete 
Sylvian fissure), this cortex is pressed downwards and backwards within the 
Sylvian fissure. And, further, the fuller development of the temporal lobe 
may press the part bordering the rhinal fissure forwards—also within the 
increasingly operculated Sylvian fissure. It is thus probable that this type 
of cortex, which borders the olfactory area in the lemur, may be the 
homolovue of the island of Reil in the higher anthropoids. 
This area has been designated, for convenience, type “R.” As it is impos- 
sible to show the whole extent of the area on the surface map (fig. 1), in 
fig. 3 a diagram of a transverse section of the Sylvian fissure has been given, 
to show the position of the submerged gyrus. 
kixtent and Boundarves.—This cortex covers (a) that part of the orbital 
surface which borders the olfactory bulb and tract:; (>) the continuation of 
this area into the gyrus lying within the Sylvian fissure; (¢) the portion of 
the temporal lobe which lies immediately above the rhinal fissure. 
Characteristics.—The depth of the cortex is about 1°8 mm. The molecular 
layer is comparatively deep, measuring about 0°25 mm. (fig. 11). The cells 
of the superficial layer of the pyramids resemble those found in the same 
position in the olfactory area, but are smaller. That is to say, they are 
of irregular triangular or quadrilateral shapes, and frequently have more 
than one branching process passing upwards. In the remainder of the 
pyramidal layer the cells are less elongated in shape than the typical 
