192 
ME. W. H. ELOWEE ON THE POSTEEIOE LOBES 
removed with the saw and bone forceps, then the dura mater was taken away, and the 
contents of the cranial cavity exposed. While still in an undisturbed condition, the 
extent to which the posterior lobes of the cerebrum projected beyond the cerebellum 
was ascertained to be fully |th of an inch. On comparing the form of the brain with 
that of the human subject, very great similarity is seen in the contour of the posterior 
half of the cerebrum, but the anterior lobes in the Monkey are much reduced, being 
narrowed almost to a point, flattened, and largely excavated in the orbital regions. 
Fig. 6 (Plate III.) is a profile view of this brain, and shows accurately the relative form 
and situation of the difierent parts while in situ, and the arrangement of the sulci upon 
the outer face of the hemisphere. 
Fig. 3 (Plate II.) is a sketch of the convolutions of the inner face of the right hemi- 
sphere. The calcarine sulcus is very strongly marked, and describes a curve ha'vdng the 
concavity up^vards ; it bifurcates as usual at the posterior end. The occipito-parietal 
sulcus, instead of running downwards and forwards as in Man and Preshytes, is directed 
somewhat backwards, and does not join the calcarine sulcus, but terminates at the upper 
margin of a prominent gyrus (the second internal annectent) which borders the last- 
named fissure superiorly. The sections show that the calcarine fissure extends to a greater 
depth than in any other genus (yet examined), and has a singular complexity of form, 
as there is concealed within it, and attached to its floor, a small but distinct gyrus 
(Plate II. fig. 3, and Plate III. fig. 7, 26). This convolution, which may be called from 
its position “ calcarine,” commences anteriorly by a slight elevation of the floor of the 
calcarine fissure, increases as it proceeds backwards, and comes to the surface where the 
sulcus turns up towards its termination ; then, bounded superiorly by the lower branch 
of the sulcus, sweeps round the inferior border of the lobe, and becomes continuous 
with the infero-occipital gyrus of the outer side. It appears to be always present ia 
Cercopitliecus, Macacus, and Cehus, and probably in all the allied genera, but is absent 
in the highest and lowest members of the order. The consequence of the depth and 
complexity of the calcarine sulcus is that the involution of grey matter forming its walls 
is much increased, and bears a very large proportion to the mass of the lobe, and the 
cornu of the ventricle is thrown quite to the outer side of the hemisphere, being at its 
termination only separated by a thin stratum of white matter from the cortical layer of 
its external face. The walls of the comu are in such close apposition that I have not 
been able to satisfy myself that it is in the adult Cercopithecus an actual cavity in the same 
sense as the remaining portion of the ventricle, especially as the staining of the lining 
membrane found in other parts rarely extends more than a quarter of an inch upon the 
surface of the hippocampus minor. But as fine sections of hardened brains show a line 
in which the cerebral substance is absent, having always the same definite extent, form, 
and direction, — as the slightest touch with the handle of the scalpel will separate the 
walls, — as in some genera it is undoubtedly as distinctly open as any other part of the 
cavity, and as it has been so considered by Geatiolet, Huxley, and other competent 
observers, I have no hesitation in looking upon it as homologous to the posterior cornu 
