IOWA ACADEMY OF SCIENCE 
217 
THE MIGRATION OF NERVOUS ELEMENTS INTO THE DORSAL AND 
VENTRAL NERVE-ROOTS OF EMBRYOS OF THE PIG.* 
BY ALBERT KUNTZ. 
With two Figures. 
That nervous elements migrate peripherally from the neural tube, during 
early embryonic development, has been observed by several investigators. Har- 
rison (’01) called attention to medullary cells migrating into the ventral nerve- 
roots of embryos of the salmon. Bardeen (’03) observed that “in mammals, 
as well as in the lower vertebrates, a certain number of cells wander out from 
the spinal ganglia and cord along with the bundles of axis-cylinder processes.” 
In his work on embryos of the chick. Carpenter (’06) has shown that cells of 
an indifferent character migrate from the ventral wall of the mid-brain along 
the oculomotor nerve and become transformed into nerve cells of the ciliary 
ganglion. In a more recent paper Carpenter and Main (’07) have described 
the migration of medullary cells into the ventral nerve-roots of embryos of 
the pig. 
In his study of the earliest differentiations in the central nervous system, 
Schaper (’97) has shown that the germ cells (Keinzellen) of His cells of epi- 
blastic origin undergoing mitotic division near the internal limiting membrane 
of the medullary tube — give rise to cells ^vhich he characterizes as indifferent, 
which migrate toward the mantle layer and are there transformed either into 
neuroblasts or into embryonic supporting cells. In the higher vertebrates some 
of these indifferent cells undergo further division by mitosis in the mantle 
layer, thus giving rise to other indifferent cells after having migrated from 
their original position. 
■ In the cells which Carpenter and Main observed migrating into the ventral 
nerve-roots of embryos of the pig, they have recognized the indifferent cells of 
Schaper. 
In studying embryos of the pig for the purpose of tracing the development 
of the sympathetic nervous system, the writer has observed medullary cells 
migrating into both ventral and dorsal nerve-roots. In transverse sections of 
embryos of the pig from 9 to 13 mm. in length, breaches of considerable extent 
in the external limiting membrane of the medullary tube may be observed in 
the region of the ventral nerve-roots. Among the fibers of the nerve-roots 
passing through these breaches cells may be observed migrating out from the 
neural tube (fig. I). I have been able to substantiate the observation of Car- 
penter and Main that cells may be found “just inside the external limiting 
membrane, in an intermediate position half in and half out of the neural tube, 
and in the base of the nerve-root just outside the external limiting membrane.” 
*From the Laboratories of Animal Biology of the State University of Iowa. 
