The ultrastructure of sensory corpuscles in the skin in the hedgehog snout.

The ultrastructure of sensory nerve endings was examined in the snout skin in 3 adult hedgehogs (Erinaceus europaeus). The material was taken intravitally under total anaesthesia and processed in a usual way for the electron microscopy. The corpuscles were evaluated in the individual sections and series sections made through the whole corpuscle. In the superficial layers of the dermis simple sensory corpuscles and free endings were found. The simple sensory corpuscles can be divided into three types. a) Corpuscles containing a greater number of lamellae in the inner core, the lamellae are arranged regularly and are separated by two opposite clefts. The capsule is formed by only several lamellae undoubtedly of fibrocytic origin. b) Corpuscles containing a smaller number of wider lamellae in the inner core situated often at random. The clefts are also irregular and are often closed in the superficial layers of the inner core. The capsule is quite simple mostly formed by a single lamella of fibrocyte which often fails to form a continuous coat of the corpuscle. c) The third type is typical of its inner core being formed by few lamellae arranged irregularly. These corpuscles have no connective tissue capsule and are separated from the environments only by the basement membrane of superficial lamellae of the inner core. The corpuscles of the second type resemble considerably the developmental stages of simple sensory corpuscles as described in the literature in the cat. They are the same in size or smaller than the corpuscles of the first type. The free nerve endings occurred in two forms. a) Flattened (lanciform) nerve terminals. The axon is rich in mitochondria. The sides of the flattened terminal is lined with one to three wide lamellae while the axon reaches as far as the surface of the formation which is covered only with the basement membrane. b) Typical free endings rich in mitochondria which are embedded in the cytoplasm of Schwann cells or occasionally are covered only with the basement membrane. The lanciform endings which are not linked up with the hairs here may represent a transition from free endings to simple sensory corpuscles.