Localisation of the corticospinal fibres in the internal capsule in man.

The myelogenetic development of the corticospinal fibres in the internal capsule was studied using eight brains of the Yakovlev Collection and two brains of the collection in Hannover Medical School. The myelin sheaths of the corticospinal fibres stained by the Loyez method can best be seen in the third postnatal month. During their course through the internal capsule their relative position changes. In the superior portion of the internal capsule, at the level of the interventricular foramen, the pyramidal tract is located in the middle of the posterior limb and in the inferior portion, at the level of the subthalamic nucleus and metathalamus, in the posterior third of the posterior limb. The classical concept of the localisation of the pyramidal tract has, therefore, to be revised for the inferior portion of the internal capsule. The result of this study confirms those of stereotactic, neuropathological and macroscopic observations and underlines the importance of the Yakovlev Collection for the neurosciences.