Abstract
Attention has been drawn to the localization of the pyramidal tract within the internal capsule of the rhesus monkey. This paper is based on experimens with 8 adult rhesus monkeys. An electrode was inserted stereotactically towards the posterior limb of the internal capsule. Its location at the internal capsule was confirmed by inducing movements of the contralateral forelimb with a current of 1 V or less, and the same site was electrocoagulated. Following the operation, the right upper extremity of the experimented animal revealed a characteristic transient paresis. Histological observations indicated that the pyramidal tract which projected the upper limb occupied the anterior third of the internal capsule. However, this conclusion is only acceptable at the horizontal level of the superior limit of the thalamus, since the pyramidal tract changes anatomical location within the posterior limb as it courses through the internal capsule.
