Demonstration of Perineural Epithelium in Whale and Shark Peripheral Nerves

Abstract

IT has been shown previously by us^1,2 that the peripheral nerve fasciculus in rat, cat, guinea pig and frog is surrounded by flat, stratified squamous epithelial layers, five in number in the sciatic nerves of the former three animals and only two-layered in the frog. The squamous cell layer surrounding the peripheral nerve fibre has also been shown by Key and Retzius³, Krenjevic⁴, Lehmann^5,6, and Rohlich and Weiss⁷. The cells of this squamous epithelium are uninucleated, the nucleus being very flat, and sex chromatin has been demonstrated in female cats and rats in these cells. In serial isolation of this epithelium we have demonstrated that the perineural epithelium represents a continuation of the pia-arachnoid membrane from the central nervous system. In a further investigation, we have been able to show³ that the lamellatod sheath of the Pacinian corpuscle is made up of the extended perineural epithelium, indicating that the pia-arachnoid not only covers the central nervous system but also covers the peripheral nervous system as a perineural epithelium extending up to and over the motor and sensory end organs.