Ultrastructure of the leptomeninx of the fetal ferret spinal cord and cerebrum.

The ultrastructures of the leptomeninx of the spinal cord and cerebrum was examined in the 32 d post-conception fetal ferret. Leptomeningeal cells of the fetal ferret spinal cord have a moderately electron dense cytoplasm and nucleoplasm. The cisternae of endoplasmic reticulum are filled with an amorphous material and are more numerous in cells covering the lateral part of the cord. Collagen fibrils are also abundant in this region. Glycogen granules are only rarely present and then only in arachnoid cells. Cells of the cerebral leptomenix have a much less electron dense cytoplasm and nucleoplasm and glycogen is present in most cells, sparsely scattered in pial cells, but more plentiful in arachnoid cells. Collagen fibrils are much less numerous and of a finer diameter than those found in the spinal leptomeninx. Cells of the spinal leptomeninx are therefore at a more advanced stage of differentiation than those of the cerebral leptomeninx.