A Quantitative Study

The University of Michigan Embryological Collection has recently acquired several specimens exhibiting stages in the genesis of a variety of malformations of the nervous system. The study of these abnormalities has stimulated a restudy of certain aspects of normal development. One phase in particular in which the need for more accurate data has been repeatedly encountered is the angulation of the spinal nerves. In such malformations as myeloschisis, the spinal cord is so anchored to adjacent body structures that no cauda equina is formed (Patten, '53). Cephalic to such defects there is abnormal traction on the cord. One means of assessing the extent of this traction is to study the degree to which spinal nerves depart from normal angulation. Again, in connection with the Arnold-Chiari malformation of the rhombencephalon the angulation of the spinal nerves offers important evidence on the moot question of cord traction as a possible etiological factor. Still another instance in which disturbances of the angulation of the spinal nerves are known to occur are tumors of the spinal cord, especially those originating early in development. There is, therefore, a real need for detailed information on the normal changes in the angulation of the entire series of the spinal nerves during the course of development. This need is especially urgent since the best studies in this general field at present available are those of