FLOWER ON THE BRAIN OF THE SIAMANO. 
281 
the Siamang {If. syndactylus ), which presents so many peculiarities 
of form, that a brief description of it may not be unacceptable as a 
contribution to our knowledge of the cerebral anatomy of the Pri¬ 
mates. As the cast taken from the interior of the skull may be pre¬ 
sumed to represent in all its proportions the brain which filled that 
cavity, I shall in future speak of it as such, and when reference is 
made to the brain of allied forms, casts of the interior of the skulls 
of adult male specimens are intended, unless otherwise specified. 
The most obvious characteristics of the general form of this 
brain (see Pig. 1) are its breadth and great depression. It even 
exceeds in flatness that of some of the lower apes, and presents a 
marked contrast to the globular brain of its ally, the Orang. The 
length of the cerebrum is 3 inches, its greatest breadth 2 5 inches, 
its height T9 inches. Its outline, when seen from above, presents a 
five-sided figure, with the angles rounded off; truncated behind, 
with lateral boundaries nearly parallel for more than half their 
length, and afterwards rapidly converging to the anterior pointed 
apex. This extremity is prolonged downwards and forwards, and 
ends in the well developed olfactory bulbs, which project slightly 
beyond the cerebrum, occupying the cavity of which the floor is 
formed by the wide cribriform plates of the ethmoid bone, and 
which has not that extremely contracted aperture seen in the Cyno- 
cephali and other lower apes. In the depressed and pointed 
form of the frontal lobes, and the position of the olfactory bulbs, the 
Siamang departs widely from the more anthropomorphous apes, in 
all of which the cerebral hemispheres are so developed in the frontal 
region as to cover the olfactories. But, on comparing this brain 
with that of a Macaque or Baboon, the under surfaces of the anterior 
lobes appear less excavated, and consequently contain a larger 
amount of cerebral substance. The temporal lobes are well pro¬ 
longed downwards, flattened on their external surface, and when 
seen from below appear narrow, and standing wide apart from each 
other. 
But the most striking peculiarity of the brain is the backward 
projection of the cerebellum beyond the level of the cerebral hemis¬ 
pheres, a circumstance, as far as I am aware, unknown in any other 
ape, either of the Old or ISTew World. On looking from above, both 
the posterior surface of the vermis, and the rounded edges of the la- 
it is in contact, so plastic that it may be pulled out, without injury, from any 
underhanging depressions in the skull cavity, and yet so elastic that it will imme¬ 
diately regain its exact form. From this a mould is made in plaster in as many 
pieces as may be necessary, according to the complexity of the form of the object, 
and out of this mould any number of casts are taken in the usual manner. These 
casts give a perfect and most convenient working model of the general form of the 
brain, which, owing to the peculiar softness of the cerebral tissues, can rarely be 
preserved in the actual specimen. Their utility has especially been insisted on 
by Gratiolet. 
