506 
PROFESSORS D. FERRIER AND G. F. YEO ON THE EFFECTS OF 
one approaching, this animal made no sign of curiosity until the person came within 
the range of vision. 
It was noted two days subsequently that the ears did not twitch when loud sounds 
were made, as they did in the other Monkeys whose hearing was undoubted. 
Daily observation was continued, and every variety of test that could be thought 
of Aas made with a view to elicit any signs of hearing, but in vain. Occasionally a 
doubt was raised, but repetition of the tests, and elimination of mere coincidences as 
regards the movements of the head, failed to establish any satisfactory evidence of 
hearing. 
A month after the operation it was placed in a cage with another Monkey, affected 
with hemiplegia. While sounds made in the vicinity invariably excited the attention 
of the hemiplegic animal, the other would go on quietly with what it was engaged 
in, without appearing to have noticed anything. 
The animal was exhibited, six weeks after the operation, before a specially invited 
number of the physiologists attending the International Medical Congress in London 
in August, 1881. While it was climbing about before the audience a percussion cap 
was suddenly exploded in its neighbourhood without causing the slightest start or 
sign of perception ;—in marked contrast to the behaviour of its hemiplegic companion 
exhibited at the same time. (See the Transactions of the International Medical 
Congress, 1881, vol. i., p. 237.) 
Six months after the operation the animal was in the same condition, in excellent 
health and spirits, and deficient in nothing but hearing. Sounds which always 
attracted the attention of the Monkeys failed to elicit any signs of perception. When 
the experiment was tried of one person going to a distance out of sight, while another 
watched, and the one in the distance called the Monkeys as if coming with food, &c., 
all the others would go to the bars of the cage and watch eagerly, while this animal 
would go on with its occupation quite unheedingly. 
Thirteen months after the operation the condition was unchanged. The animal 
was perfectly well, in full possession of all its other faculties, but manifestly totally 
deaf. 
It was killed with chloroform. 
Post-mortem examination .—The orifices in the skull were covered by membrane 
which was adherent to the brain at these points, but there were no adhesions.or 
abnormalities at any other part. 
The left hemisphere .—The membrane was adherent over the lower extremity of 
the anterior limb of the angular gyrus, and over the region corresponding with the 
position of the superior temporo-sphenoidal convolution. This had entirely disap¬ 
peared, its place being indicated by a groove, which was deepest at the lower 
extremity. A small portion of undestroyed cortex was seen at the lower extremity, 
separating the groove from the commencement of the fissure of Sylvius. Elsewhere 
there was no trace of the superior temporo-sphenoidal convolution (Plate 22, fig. 24). 
