14 Proceedings of the Royal Physical Society. 
their brain-being markedly pointed as compared with that 
of man. The vertical extent of the frontal lobe is also greatly 
diminished by the upward projection of the roof of the orbit. 
Taken as a whole, therefore, the frontal lobe is relatively 
much smaller in the anthropoids than in the human subject, 
and the diminution specially involves the outer part, of the 
lobe. These facts, taken in connection with the discovery 
of Broca of the seat of articulate language in the inferior 
frontal convolution, lend a certain amount of probability to 
the contention of Bischoff and others that this convolution 
is either absent or very poorly represented in the apes. 
Gratiolet recognised in the brain of the apes superior middle 
and inferior frontal convolutions corresponding to those found 
in man, and Cunningham, after a very careful and elaborate 
investigation of the comparative and developmental anatomy 
of the frontal fissures, supports the éonclusions of Gratiolet. 
In the New-World monkey, Cebus albifrons, the outer surface 
of the frontal lobe shows two fissures. One of these has a 
T-shaped form, its vertical limb dividing above into an 
anterior and a posterior branch. Eberstaller and Cunning- 
ham believe this to be the inferior preecentral sulcus. ~The 
other fissure runs from the anterior end of the brain back- 
wards towards the preecentral sulcus, and ends below its 
anterior branch. This fissure, generally known as the gyrus 
rectus in the apes, is supposed by some to be absent in man ; 
but Cunninghain holds that this gyrus rectus represents the 
inferior frontal sulcus of man. The frontal fissures show a 
gradually increasing complexity as we advance from the 
lower to the higher forms of the Primate brain. According 
to Cunningham, the human frontal lobe is distinguished from 
that of the chimpanzee by the fact that its superior frontal 
convolution is generally divided into two parts by a sulcus- 
frontalis mesialis. This fissure, however, is absent or poorly 
developed in the brain of the Negro. Further, in man the 
inferior frontal convolution possesses two Sylvian opercula, 
a frontal and an orbital, both of which are completely absent 
in the anthropoids, so that in them a portion of the island 
of Reil is uncovered and exposed on the surface of the 
cerebrum. : 
