. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. QE3f£IlAL PAliT. sheaths, which are prolonged over their processes and so over the nerve fibres. Very generally several ganglion cells are enclosed in a common sheath. Nerve fibres are either centrifugal, , they carry nervous impulses from the central organ to the peripheral organs (motor, secretory nerves) ; or they are ceutripo- tal, , they carry them from the periphery to the central organs (sensory nerves). They are prolongations of ganglion cells, and, like them, are fre-. FiG. 38.—Nerv
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. QE3f£IlAL PAliT. sheaths, which are prolonged over their processes and so over the nerve fibres. Very generally several ganglion cells are enclosed in a common sheath. Nerve fibres are either centrifugal, , they carry nervous impulses from the central organ to the peripheral organs (motor, secretory nerves) ; or they are ceutripo- tal, , they carry them from the periphery to the central organs (sensory nerves). They are prolongations of ganglion cells, and, like them, are fre-. FiG. 38.—Nerve fibres (partly after M. Schultze). a, non-medullated sympa- thetic fibre, b, medullated fibres, one of them with commencing coagulation of the axis cylinder, c, medullated ner\'e fibre with the sheath of Schwann. Fio. 37.—a bipolar ganglion cell. 6, nerve cell, from the human spinal cord (anterior cornu), (after Gerlach). P, pigment body. quently enclosed in a nucleated theath. The larger and smaller nerves are composed of a number of such fibres bound together. According to the minute structure of the nervous sub- stance we distinguish two kinds of nerve fibres—(1) the so-called medullated nerves, with a double contour; (2) the non-medullated or naked axis cylinders (fig. 38, a, b, c). The former are distinguished by the fact that, on the death of the nerve and as the result of coagulation, a strongly retractile fatty substance which forms a sheath for the nerve fibre comes into view. This sheath is known as the medullary sheath, and the central fibre as the axis cylinder. The medullary sheath disappears near the ganglion cell, the axis cylinder only entering the protoplasm. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Claus, Carl, 1835-1899; Metcalf Collection (North Carolina State University).
Size: 1631px × 1532px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
