THE BRAIN OF THE LOWER ANIMALS 183 
that cases of arrested development of this orphan are always 
accompanied by imbecility or even idiocy. Moreover, in all 
animals the degree of intelligence varies with the relative size 
of the cerebrum as compared with other parts of the brain. 
The brain in the higher members of the order Primates 
is quite distinct in type from that of the Lemurs and all 
quadrupeds, i.e., the cerebellum is entirely covered by the 
cerebral hemispheres as it is in man. Although the brains of 
the three large “ man-like ” apes — the Gorilla, Orang-Outang, 
and Chimpanzee — are clearly distinguishable from one another, 
it is impossible to say that any one of the three is of higher 
conformation than the others. For example, the brain of the 
Orang comes first with regard to the number and complexity 
of the convolutions, whereas that of the Gorilla takes first place 
by the greater vertical height of the cerebral hemispheres. 
Again, the width of the latter as seen from above is perhaps 
greatest in the Chimpanzee, though on the whole this ape 
has a simpler brain than either the Orang or Gorilla. 
Among other orders of the mammalian class no definite 
relation has been traced between the type of brain and the 
intelligence of the animal ; for instance, while in the Beaver 
the cerebral hemispheres are almost smooth, they are more 
convoluted in the sheep than in the dog. The explanation of 
this apparent anomaly may perhaps be found in the fact that 
these three quadrupeds belong to three different orders, for in 
animals which are closely allied to one another, there is un- 
doubtedly some relation between intelligence and complexity 
of brain. Accordingly we may observe that the brain of the 
dog is rather more comple.x than that of the cat, more than 
half the cerebellum in the latter animal being visible from 
above, whereas in the dog it is almost covered by the brain 
proper. It is a remarkable fact that the Cetacea have more 
complex brains than any other group of mammals, except the 
“ man-like apes ” and the elephant — the most sagacious of 
quadrupeds. 
Although no definite serial order can be traced from the 
lower to the higher orders of mammals, it is manifest that 
the brain of the “ man-like ” ape shows almost as great an 
advance in type over that of even the most intelligent quadru- 
peds as the latter show over birds. There is little doubt that 
the mental powers of all animals are largely dependent on the 
development of a special sense endowment ; thus the Quadru- 
mana have the sense of touch almost as highly developed as 
man himself, and this is also the case with the elephant. Like- 
wise among the flesh-eaters the superior intelligence of the dog 
may be largely due to his abnormal sense of smell ; however, 
the mental faculties of the wild dog are not very different from 
those of the wolf. It would seem, therefore, that it is only his 
long association with mankind — dating back to prehistoric times 
— that gives the dog his mental superiority over these two last- 
