MOTOR CORTEX AND INTERNAL CAPSULE IN AN ORANG-OUTANG, 133 
Method of Investigation. 
In accordance with onr present mode of recording the results of excitation of the 
cortex cerebri, we proceeded to expose and explore the surface of the so-called motor 
region in the left hemisphere in the following manner ;— 
1. Anwsthetisation. —The animal was thoroughly narcotised with ether. It was 
interesting to note that, in harmony with the greater size and the more highly 
evolved intelligence of the animal, it required, relatively, as well as of course absolutely, 
more ether than the lower Macacque Monkeys do. 
2. Operation .— The brain was exposed by the method described elsewhere (‘ Brit. 
Med. Journ.,’ 1887). The large flap of scalp and segments of the dura mater were 
carefully replaced after each measurement of the surface {vide infra) or excitation, 
so as to entirely preclude the possibility of the cortex becoming damaged by drying 
and cooling. For the special prevention of the two latter sources of error, the 
temperature of the room was maintained at 75°-80° F., the animal was placed upon a 
hot tin (temperature about 100° F.) and, finally, the surface of the brain was 
occasionally irrigated with w^arm '75 per cent, salt solution. 
We found that these precautionary measures preserved the excitability of the 
cortex at its normal level for many hours. 
3. Method of Recording. —The positions of the sulci of the area exposed were then 
transferred by means of fine compasses to paper ruled mathematically with squares, 
whose sides measured 2 mm. We thus obtained a projection of the configuration of 
the cortex, the surface of which was already divided into squares of 4 square mm."''' 
in extent. The actual drawing made at the time of the experiment is seen in fig. 3. 
Each of these squares was then excited, the strength of the minimal stimulus 
noted, and also the resulting movement evoked. 
4. Mode of Excitation. —The excitation was provided by the current from the 
secondary coil of a Du Bois-Reymond inductorium, furnished with a 1 litre bichro¬ 
mate cell. No side wire was employed {vide strength required mfra). The electrodes 
were fine platinum points, 2 mm. apart, and they were applied horizontally, i.e., in 
the long axis of the brain, each electrode resting on the mid point of the two sides 
of each square. 
The strength of current required to evoke any movement was notably in excess of 
that which we have found necessary to use in the Macacque. With the Orang a 
minhnal stimulus {i.e., the weakest which would produce a movement) was obtained 
only when the secondary coil was moved to 9'5 centims. from the zero point of 
completely covering the primary coil. This current was such as to cause discomfort 
bordering on pain when applied to the tip of the tongue of the experimenter. This 
(minimal) stimulus was used throughout. 
The method of investigating the internal capsule is given further on; see p. 147. 
* Tliroughout this paper we shall refer to these units of localisation as “squares.” 
