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Because of the lack of agreement existing in respect to the origin of the pyramidal tract, it was thought that the application of a refined silver stain to the lower part of the human pyramid might give a clue as to its cells of origin and, in addition, furnish information about the size and number of its component fibers. It is commonly taught that the fibers of the pyramidal tract originate from the gigantopyramidalis cells of Betz in the motor area (area 4). As these cells are the largest found in the cerebral cortex, it is logical to assume that they give rise to reasonably large fibers. These cells, although conspicuous by their size, are not abundant numerically. On the basis of counts made by Campbell,1there are about 25,000 Betz cells on one side of the human cerebral cortex. In contrast to this, Weil and Lassek,2using
A. M. Lassek (Wed,) studied this question.