196 
ME. W. H. ELOWEE ON THE POSTEEIOE LOBES 
border of each lateral lobe. The extreme projection was T5 of an inch behind the cere- 
brum. In front the olfactory lobes extended i^th of an inch beyond the cerebrum. 
The hemispheres were 1-65 inch in length, and 1-3 inch across their broadest part. On 
gently separating the edges of the longitudinal fissure, the corpus callosum was seen to 
cover completely the corpora quadrigemina ; its length was '85 of an inch. 
The brain was now removed. The general surface of the cerebrum is smooth, but 
marked with strongly defined, deeply cut, regular, and almost symmetrical sulci. The 
anterior or frontal lobes are attenuated, being flattened above, compressed laterally, and 
excavated below for the orbital plates. They are distinctly marked ofiF from the tem- 
poral lobe by the fissure of Sylvius, which runs upwards and backwards to the parietal 
region, and has an abrupt and slightly bifurcated termination. The average depth of 
this fissure is nearly one-fourth of an inch, and on separating its lips, a small, smooth, 
but distinctly defined insula or median lobe of oval form was disclosed. This obseiwa- 
tion is important, as Geatiolet says, “ Le lobe central [insula] parait particulier a 
I’homme et aux singes ; peut-etre voit-on quelque chose d’analogue dans les makis, mais 
on ne voit rien de semblable chez les autres mammiferes.” The temporal lobe is full 
and deep, and terminates posteriorly without any definite boundary in the posterior or 
occipital lobe. This last is shallow, and excavated on its under and inner surface for 
the cerebellum. 
The sulci on the outer face of the hemisphere are — 1. The fissure of Sylvius (e). 
2. A well-marked longitudinal sulcus on the upper surface of the frontal lobe, inclining 
outwards posteriorly, probably corresponding with the infero-frontal (a). 3. A slight 
longitudinal indentation on the orbital surface of the same lobe. 4. A very distinct 
sulcus on the temporal lobe, parallel to, but extending rather higher than, the fissure 
of Sylvius, and curving forwards at its upper end (f) : this is the antero-temporal 
(scissure parallele). 5. A well-marked longitudinal sulcus on the upper surface of the 
parietal, and extending into the occipital lobe, marking off the upper limit of the 
angular gyrus. 6. A slight longitudinal indentation on the outer side of the occipital 
lobe. There is no trace of the temporo-occipital sulcus (scissure perpendiculaire ex- 
teme), so well marked in the higher Apes, or of either of the parietal fissures ; indeed 
the region on which they should be placed is very greatly reduced. In number, extent, 
and situation the sulci above described nearly correspond to those of Callitlirix moloch 
(as figured by Geatiolet), a Platyrrhine Ape about the same size as the Lemur. 
Upon the internal face of the hemisphere (Plate III. fig. 14) are seen — I. The calloso- 
marginal (^), distinct only in the middle third of the hemisphere. 2. A very deeply marked 
calcarine sulcus [I, Z), extending from below the posterior end of the corpus callosum, 
backwards and slightly upwards, to near the extremity of the hemisphere, where it ends 
abruptly without bifurcation. 3. Joining this, almost at a right angle, is the occipito- 
parietal ijc), which does not quite reach the upper margin of the hemisphere. 4. A shght 
indication of the collateral sulcus (w). 5. A well-marked dentate sulcus (m). 
The olfactory bulbs are in size intermediate between those of the lower Apes and 
