OP THE CEKEBEIJM OE THE QUADETJMANA. 
193 
in Man. Wliether it is an actual or potential cavity is, however, of very little con- 
sequence, as there can be no question that the portion of the brain answering to that 
which in Man is called hippocampus minor, attains in Cercopithecus a really prodigious 
development in comparison with the size of the cerebral hemisphere. 
The proportionate length of the posterior lobe, as measured upon a section made 
while the base of the brain still remained within the cranium, slightly exceeds that of 
Man, being to the antero-median portion as 54 to 100. 
Macacus. — The brains of M. silenus, M. nemestrinus, M. cynomolgus, M. sinicus^ M. ra- 
diatus, and M. erythrceus have all been examined. They resemble one another so closely 
that the latter (the Rhesus Monkey) alone need be described. The length of the poste- 
rior lobes, both as to the extent to which the cerebellum is covered, and as ascertained by 
internal measurement, is slightly inferior to that of Cercopithecus. The convolutions of 
the inner face of the hemisphere (Plate II. fig. 4) have the same general arrangement as in 
that genus. The calcarine sulcus does not extend to quite so great a depth, but it con- 
ceals within it, though on rather a smaller scale, a similar gyrus (Calcarine, No. 26 B, 
Plate II. fig. 4). In adult examples the walls of the posterior cornu adhere very closely, 
but in a new-born Rhesus they were distinctly separate almost to the very end of the 
lobe. In this specimen the hemispheres were so elongated backwards as to project by 
nearly one-fourth of their length beyond the cerebellum. 
Cynocephalus. — Geatiolet has demonstrated that the principal cerebral characteristic 
of this genus is the great development of the occipital lobes. In a nearly full-grown 
example of C. porcarius, I find that they project ^^ths of an inch beyond the cerebellum, 
or rather more than ^th of the entire length of the hemisphere ; proportionally more, 
therefore, than in Man. Measured internally, the proportion of the posterior to the 
antero-median portion of the cerebrum is as 67 to 100 — greater than in any other of the 
Catarrhine Apes. The calcarine sulcus is very deep and complex, as in the last two 
genera, but the specimen did not reach my hands in time to give any drawings. 
Family 2. Platyrrhina. 
Cehus apella. — The brain of this species presents a different form from that of Cerco- 
pithecus^ or any of the Old World Apes. The hemispheres are much elongated and 
compressed laterally, so as to give a regularly oval outline to the entire cerebrum 
when seen from above. The cerebellum, though large, is entirely covered, and the 
posterior lobes are of great proportional length, being to the antero-median as 59 
to 100. 
The sulci upon the inner face of the cerebral hemisphere are shown in Plate III. fig. 5. 
The calcarine fissure at its anterior extremity joins the dentate, so that the callosal gyrus 
is not actually continuous with the uncinate as in Man and most of the Quadrumana ; but 
at the point of union the sulcus is extremely shallow, or, in other words, the band which 
connects the two above-named gyri does not quite reach the surface. At first the 
sulcus runs somewhat in a downward direction, but ultimately takes a considerable 
MDCCCXLII. 2 c 
