1908.] Cell Lamination of Cerebral Cortex of the Lemur. 491 
III. GENERAL DESCRIPTION OF THE BRAIN. 
The lemur’s brain measures about 5 cm. by 3°5 cm., and weighs on an 
average about 19 grammes. The surface is broken by few fissures. There 
is no occipital lobe, the cerebellum being only partially covered by the 
cerebral hemispheres (vide fig. 1). 
The olfactory bulbs and: tracts are comparatively large, and the rhinal 
fissure is seen on the lateral surface of the temporal lobe. It is therefore 
evident that the lemur has a well-developed olfactory area. 
On the dorso-lateral surface there are four main fissures, which, according 
to the nomenclature of Elliot Smith (1), may be termed the sulcus rectus, 
the lateral sulcus, the Sylvian fissure, and the parallel sulcus. Two small 
fissures are found on the fronto-orbital surface—the orbital, near the anterior 
pole, and behind it the fronto-orbital. On the mesial surface are seen the 
bifurcated calcarine fissure, the intercalary sulcus, and the hippocampal 
fissure. ‘The latter gives off a branch in front of a small hippocampal 
tubercle. A short fissure, called by Elliot Smith the inferior occipital 
sulcus, lies on the under surface of the occipital region. In some species a 
small sulcus rostralis can be seen on the fronto-mesial surface. To these 
more prominent fissures may be added a few others, which though small and 
shallow are constant. The most anterior of these lies in the middle of the 
triangular space formed on the dorsal surface by the sulcus rectus, the 
anterior part of the sulcus lateralis, and the border of the mesial surface, 
and is probably the homologue of the sulcus cruciatus of the carnivora. 
Between the superior extremities of the Sylvian fissure and of the parallel 
~ sulcus a small series of fissurets is usually present, tending to join the two 
sulci. This has been pointed out by Elliot Smith, who observes that in 
the aye-aye the communication is complete, as in the lower mammals, and 
the two fissures form one continuous arch; but that in the primates these 
fissures are always separated. Some shallow linear depressions are seen near 
the margin of the posterior pole. The superior of these, which is constant 
although it varies a little in position, is possibly an indication of a rudi- 
mentary “ Affenspalte.” | 
The lemur’s brain forms an interesting study for comparison with the 
brains of carnivora, ungulates and the apes. Whereas in size, in simplicity 
of convolutional pattern, in the uncovered cerebellum, and in the well- 
developed olfactory area and bulbs, it is allied to the lower mammals’, 
in many respects it bears resemblance to the ape’s brain; notably in the 
bifurcated calcarine fissure, the separate intercalary sulcus, the more com- 
pletely developed Sylvian fissure, and the separation of this fissure from the 
parallel sulcus. 
