174 
NATURAL HISTORY. 
see what this long slender organ is doing, that most children think there is an eye at the end of it. 
Directly the Spider Monkey rises on its hind legs, up goes the tail straight behind its back, and curves 
a little at the tip downwards : the delicate hairs stick out and feel the slightest touch or passage of 
air ; and the least touch induces the last few joints to clasp hold. The animal will walk along and 
catch hold of things with its tail at every other step or so, and will change its hold in exact propor- 
tion to its rate of progression. All these movements necessitate clasping, unclasping, twisting, and 
a regular succession of efforts, and are not likely to Ixj carried out except by an animal with a well- 
developed nervous system. Hence it has been a matter 
of some interest to compare the brain of Ateles with those 
of other Monkeys, and even with that of man. 
Even in this Monkey, which is low in the scale on 
account of its having badly-developed thumbs, the struc- 
tures of the brain greatly resemble those of the Monkeys 
of the Old World. The nerves are large in proportion to 
the substance of the brain, and the brain proper is narrow 
in front and hollowed out beneath, where it rests on the 
orbits. But these proofs of a low kind of intelligence and 
of great muscular power are accompanied by structures 
which mimic or sketch out those of the human brain in 
an extraordinary manner. The cerebellum, or little brain, is large, as it is the organ which has much to 
do with regulating and co-ordinating the movements of the muscles, but it is quite covered by the back 
part, or posterior lobes, of the brain. Inside the brain the cavities called the 
ventricles may be seen, and they are made on the human plan, for the cavity on 
either side (lateral ventricle) has a front part, a back part, and a deep one, and on 
its lower surface, or floor, certain roundings, which are called by odd names, such 
as the hippocampus minor and the hippocampus major. These are visible in the 
brain of Ateles as they are in man. How, it is very remarkable that, allowing for 
the difference in the size of the brain of most other Monkeys and of man, that 
the Spider Monkey should have larger posterior lobes to its brain than they have. 
Moreover, this unusual size produces a greater length of the back part (or horn, 
or cornu) of the lateral ventricle in Ateles. The difference, however, between the 
packing of the nervous substance of the brain in man and in the Spider Monkey 
is vast, for in this last there are few convolutions, but the principal are happily 
said by Huxley to sketch out the position of the most important in the human 
brain. The projection of the back part of the brain of the Spider Monkeys over 
the cerebellum is at least one-tenth of an inch. Hence there is much nervous 
matter in the back part of the brain, and this compensates for the narrowing and 
diminution of nervous matter in the front. Are the nerves, then, which give the 
Spider Monkey its wonderful power of activity and complicated movement, situated 
in the back part of the head 1 At present physiologists have not satisfactorily 
shown what are the offices of these back or occipital lobes of the brain; the rounded 
floor of the cavity in the brain, which goes by the absurd name of hippocampus, 
because it is curved like a “ sea horse,” and which is well seen in Ateles, has much to do with the 
sensation of touch, and the nervous matter at the sides of the brain appears to be connected with 
the nerves of the muscles of the limbs. The Ateles lead a life of very great sameness in their forests, 
and their perceptions and intelligence are never greatly stimulated, hence the fore part of the brain 
is small. 
THE COAITA * 
This is the Monkey of which an extraordinary story is told by Acosta. It belonged to the 
Governor of Carthagena, and was regularly sent to the tavern for wine. They who sent him put an 
JAW OF THE SPIDER MONKEY. 
* Ateles paniscus. 
