The present investigation is a continuation of anatomic studies on the pyramidal tract of man and is directed at a classification of the large cells of the motor cortex (area 4 of Brodmann). In spite of the fact that the cells designated as Betz or giant cells are probably the best known in the cerebral hemisphere, it is not possible to give an unequivocal description of them. As Cobb1 said, "No definition is given as to how large a 'giant' cell has to be to deserve that name." Yet these elements, whatever their volume, are commonly said to give entire origin to the pyramidal tract fibers and thus to control isolated movements. With respect to this question Walshe2 said:
... the statement that "giant cells" alone give rise to pyramidal fibers has no meaning unless we are agreed as to what constitutes a giant cell. On examination we find