Lrsem, Fore-Brain of Macacus. 5 
theory we may homologize the upper frontal gyrus of Macacus 
with the first frontal of man, and the remaining lower gyrus 
with the second frontal. 
The mesial aspect of the frontal lobe presents the marginal 
gyrus enclosed by the calloso-marginal fissure. The gyrus 
fornicatus is continuous with that portion of the frontal lobe 
which in man is known as the precuneus. 
We have already noted the concave non-developed orbital 
surface of the frontal lobe. 
The Parietal Lobe. 
The parietal lobe has two surfaces; an external one 
bounded anteriorly by Rolando, inferiorly by Sylvius, and pos- 
teriorly by the ‘‘Affenspalte,’’ and a mesial surface which is 
continuous with the gyrus fornicatus. The external surface 
presents the intra-parietal fissure. This sulcus lies between the 
fissure of Rolando and the external occipital sulcus. ~It starts 
a little posterior to the fissure of Rolando, and passes upwards 
and backwards. Then it curves upon itself, and terminates in 
the par-occipital sulcus. The intra-parietal fissure was origi- 
nally composed of three distinct fissures, a superior, an inferior, 
and a horizontal parietal sulcus. This condition is still evident 
in the adult human brain where the three parts of the intra- 
parietal sulcus are separated from one another by numerous 
annectent gyri. 
The external surface of the parietal lobe presents two gyri, 
a superior and an inferior parietal gyrus. The superior parietal 
gyrus represents the ascending parietal and the superior parietal 
convolutions of man. The inferior parietal gyrus may be 
divided into supramarginal and angular convolutions. The 
supramarginal is bounded anteriorly by the intra-parietal sulcus, 
posteriorly by the parallel fissure, and inferiorly by the fissure 
of Sylvius. The angular is bounded in front by the temporo- 
sphenoidal sulcus, below by the inferior occipital, and behind 
by the external occipital. 
