THE BRAIN IN THE ANTHROPOMORPHA. 411 



3erebriim, wliich, in this antliropomorplioiis Ape, do not over- 

 lap the cerebellum as they do in all the others. 



The cerebral hemispheres are higher in proportion to their 

 length in the Orang than in the other AntliroponfiorpTia j but, 

 in all, they are elongated and depressed, as compared with 

 those of Man. The frontal lobes taper off anteriorly, and their 

 inferior surfaces are excavated from without downward and 

 inward, in correspondence with the projection of the upwardly 

 convex roofs of the orbits into the cranial cavity. The pos- 

 terior cornu of the lateral ventricle is always well developed, 

 and contains a prominent hippocampus minor and eminentia 

 coUateralis. An occipito-temporal or "external perpendicu- 

 lar " sulcus is always present. It is most nearly obliterated in 

 the Orangs. All the gyri of the human brain are represented 

 in the cerebral hemispheres of the Chimpanzee ; but they are 

 simpler and more symmetrical, and larger in proportion to the 

 brain [see Figs. 21 and 22). The fissure of Sylvius is less in- 

 clined backward, and that of Rolando is placed more forward 

 than in Man. The insula has simpler and fewer radiating sulci, 

 and is not completely hidden by the temporal lobe. Only the 

 second, third, and fourth annectent gyri appear upon the sur- 

 face. The first remains folded upon itself, and gives rise to 

 the characteristically simian occipito-temporal or external per- 

 pendicular sulcus. The occipito-parietal sulcus, on the inner 

 face of the hemisphere, is much more nearly perpendicular 

 than in the human brain. The corpus callosum is relatively 

 smaller ; the septum lucidum is very thick, and the precom- 

 missural fibres are well developed. The vermis is small in 

 proportion to the lateral lobes of the cerebellum, and the iloc- 

 culi are relativelv small, and lie below the latter. 



The whole cerebellum is larger in proportion to the cere- 

 bral hemispheres; the latter being to the former, as 8 J to 1 in 

 Man, but as 5f to 1 in the Chimpanzee.* The nerves are 

 larger in proportion to the brain than in Man. There are no 

 corpora trapezoidea^ such as exist in the lower Mammals, and 

 the corpora alhicantia are double. 



In all the Anthropomorpha^ the inner incisors are larger 

 than the outer, in the upper jaw ; smaller in the lower jaw. 

 There is a diastema, though it is often but small in the female 

 Chimpanzees. The canines are large and strong, and may be 

 grooved longitudinally on their inner sides. The premolars 



* It must be recollected that the brains of young anthropomorphous 

 Apes, only, have been examined. Perhaps this has to do with the absence of 

 mineral deposits in the pineal gland of the Apes. 



