1911.] Motor Localisation in the Brain of the Gibbon. 71 



lobe along the external surface to the anterior extremity. The electrodes 

 placed elsewhere on the occipital lobe gave no movements. It may there- 

 fore be inferred that owing to the infolding of the cortex to form the fissure 

 stimulation of this region by bipolar excitation extended to a sufficient 

 number of motor neurones, or that it is in this region indicated in fig. 1 E by 

 area 28 that the optic radiations terminate in greater numbers than elsewhere 

 in the occipital lobe. 



Again, it is probable that unilateral stimulation was inefficient in the 

 production of adduction of the vocal chord, because this experiment was the 

 last performed. Definite movements were obtained for a short time, however, 

 by bipolar stimulation of the region 26 indicated; later on, however, the 

 same strength of stimulus failed to give any response, and the animal was 

 killed. 



It is of interest to note that unipolar stimulation gave no result when 

 applied to the ascending parietal convolution ; this fact, as we shall see, 

 accords completely with the histological observations. 



Histological Observations. 



At the close of the experiments, after the animal had been killed, the 

 brain was hardened in situ by an injection of formalin solution through the 

 carotid artery. It was thought that in this way the structure of the cells 

 would be best preserved. Subsequent examination showed that this 

 anticipation was not realised, for the preservation was not sufficiently 

 good to make a_ complete survey of the cell lamination of the whole brain 

 profitable. It was, however, quite adequate for the purpose of determining 

 the extent of the principal areas in the lateral and mesial surfaces of the 

 frontal lobe. For this purpose the brain was divided into blocks, arranged in 

 such a way as to avoid, as far as possible, the necessity of cutting any part of 

 the cortex obliquely or tangentially, and the planes of section were plotted 

 carefully on outline drawings of the surface of the hemispheres. After the 

 blocks had also been drawn, they were embedded in paraffin in the usual way, 

 and cut into sections parallel to their faces. The sections were stained with 

 polychrome methylene blue. 



Both hemispheres were examined, but the results have been mapped only 

 on the drawings of the right hemisphere (figs. 2 and 3). Since the types of 

 cortex here dealt with have been often and fully described and figured, and 

 since their structure in this case presents apparently no unusual features, 

 special descriptions or drawings have not been given. 



Figs. 2 and 3 show the distribution of two quite distinct types -of 

 cortex in the lateral surface of the Gibbon's brain. That portion which is 



