THE UNCROSSED PYRAMIDAL TRACT

The uncrossed pyramidal tract, the subject of this paper, is not the normal tract of uncrossed pyramidal fibers in the anterior column that occurs in man and a number of other mammals, but the pyramid that without crossing at the transition of the medulla and thc cord proceeds en masse in the ipsilatcral half of the cord. As is generally known the majority of the pyramidal fibers at the caudal end of the medulla in man cross from the anterior position to the lateral column of the contralateral half of the cord. A small nuinher of fibers, about one fifth of the total amount, proceed on their way unchanged and a very small number go laterally and dorsally to the ipsilateral lateral funiculus. Only cases in which the massal crossing of the pyramid at the transition of the medulla and the cord does not take place are the subject of this paper. In such cases the whole pyramidal tract just remains in the anterior part of the neuraxis and descends in the anterior column of the cord. So the pyramidal crossing, the most conspicuous feature of the lowest levcl of the medulla, is missing and a cross section at this level in such cases presents a very uncommon aspect. The pyramidal crossing is frequently asymmetric; in such cases many inore fibers cross from one side than from the other one. Consequently the anterior funiculus of the cord on one side is much larger than on the other, and one half of the cord contains a much greater number of pyramidal fibers than the other. Total lack of the massal crossing of pyramidal fibers a t the usual level, however, seems to be rare, and as far as could be ascertained

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