[Structure of the perineurium of the peripheral nervous system]

The structure of the perineurium in different parts of the peripheral nervous system of rats, rabbits and cats was studied by light-optical and electron microscopic methods. The structure of the perineurium in all the animals studied is sim8lar and consists of different number of the epithelial type layers of the perineural cells, with bundles of cooagnous fibres between them. The greatest anount of layers is found in the perineurium of the sensory and vegetative ganglia, their amount being less between the nerve trunks and bundles. Solitary sensory mielinated nerve fibres are surrounded with a perineural etui consisting of one or two cellular layers. The thickness of the perineural cells varies from 300 to 1500 A and only in the nucleus field it is equal to 1-2 mu. Every layer of the perineural cells is surrounded by a basal membrane. In their cytoplasm there are many pinocytic vesicles in addition to main organells. Between the perineural cells there exist close contacts. The internal layer of the perineurium is the place of origin of intraganglionic septa and in certain distance surrounds the vessels entering the ganglion. Ultrastructurally the perineural cells are similar to the endothelium of the vessels.