The postnatal development of sensory nerve endings has been studied in the skin of the planum nasale of the cat. The Merkel nerve endings develop in the prenatal period; after birth some redundant axons perish. Up to the third postnatal day, sporadic Merkel cells and nerve terminals still can be observed in the stratum papillare of the dermis. The free nerve endings in the dermis appear before birth. In the postnatal period the nerve fibres as well as the nerve endings ramify. A few of them come into contact with the stratum basale of the epidermis, others may perish. Most of these nerve endings are located in the stratum papillare of the dermis. The simple encapsulated corpuscles with an inner core develop after birth. In the depth of the dermis, the corpuscles are arranged mainly in groups, in the stratum papillare, however, they are more isolated. The development of those corpuscles, located in the depth of the dermis, already begins before birth and finishes mostly about the 39th postnatal day. The development of the corpuscles in the stratum papillare starts later and ends between the 3rd and 4th month. The nerve terminal of the corpuscle changes only slightly during development. It elongates, becomes thicker, and the number of mitochondria increases. During all stages it sends cytoplasmic spines in between the lamellar system of the inner core. The inner core is formed by cytoplasmic lamellae of the peripheric glial cells. In the course of development the number of cytoplasmic lamellae increases, they become thinner and gradually each one will be covered by a basal lamina. A mature corpuscle possesses an inner core with one or two longitudinal clefts. These clefts occur more frequently in corpuscles with complete capsules. The connective tissue cells primarily form a primitive capsule around the inner core. During development the layers of the capsule increase in number. Mature corpuscles have a one- to four-layered capsule. The capsular cells are then ensheathed by a basal lamina.
