An electron microscopic study of the pericytes of the developing capillaries in human fetal brain and muscle.

Capillaries of the developing cerebral cortex were examined by electron microscopy and compared with those developing in the superior rectus oculi muscle. The pericytes of cerebral vessels were found to be of very elaborate form and involved in complex 'peg and socket' relationships with endothelial cells. They were numerous and formed an almost complete investment of the endothelium. In the muscle, by contrast, pericytes were rare, although often of complex form. Cerebral capillaries were always completely and closely invested by neuropil, in marked contrast to the very loose connective tissues in the vicinity of muscle capillaries. The significance of the findings is discussed.