THE CORTICOSPINAL tracts are present in all Mammalia and have provoked more studies than any other tract. Nevertheless, the vast literature contained little ontogenic information until Humphrey's account of human corticospinal tract development.1 Perhaps one reason for the lack of ontogenic data is that investigators have despaired of operating on the mammalian fetus to study the dynamics of tract formation. Efforts of the few previous workers in fetal surgery2-5 have now been extended by personal experiments showing that the rat fetus can survive a variety of neurosurgical operations. The fetus can then be delivered and nurtured into adulthood by a few simple techniques.6 Thus far, rats have survived postnatally after intra-uterine spinal cord transection, destruction of one hemispheric wall, destruction of the dorsal column nuclei, destruction of the rhombic lip, or optic enucleation. The rat fetuses were operated on during day 15.5 or 16.5 of gestation,
DeMyer W. Ontogenesis of the Rat Corticospinal Tract: Normal Events and Effects of Intra-Uterine Neurosurgical Lesions. Arch Neurol. 1967;16(2):203–211. doi:10.1001/archneur.1967.00470200091008
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