SHEATH

n. Sheth. Gr., lAvrpov. Lat., vagina. Fr.. gaine. Ger., Scheide. 1. An enveloping structure, a case or covering. 2. In botany, see VAGINA (3d def.) and BUNDLE s. Axis-cylinder s. See Huxley's LAYER. Capillary s. See Cir cum vascular a. Cellular s. See EPINEURIUM. Cir cum vascular s. A wide lymphatic tube completely surrounding the smallest blood-ve els of bone, of the central nervous system, of the retina, and of the liver. [a, 34.] Cortical s. Of Nageli, the whole of the primary bast bundles, [a, .] Dentinal s. Ger., Zahnscheide. Of Neumann, the s.-like structure (supposed to be an elastic limiting layer) lining the dentinal canals and thus containing the dentinal fibres [J 32 35.] Dural s. See DURA. Elastic s. of the axis-cylinder.' See Mauthner's s. Fibril-s. Ger.. Fibrillfii-Hciutctien (oder Scheide). 1. Of Key and Retzius, a kind of s. for the individual nerve-fibres of a nerve funiculus, formed outside the primitive s. of the nerve-fibril by the longitudinal connective-ti ue fibrils of the endoneurium. [" Arch. f. mikr. Anat.," 1873, p. 308 (J).] 2. A supposed membrane inclosing the muscle columns and appearing as a sharp, clear line around Cohnheim's areas. [DBnitz, " Arch f Anat. und Phys.," 1870, p. 436 (J).] Henle's root-s. (of the hair). See Henle's LAYFR. Henle's s. \. See Henle's LAYER. 2. Of Ranvier (1878), the connective-ti ue envelope of the finest fasciculi of medullated nerve-fibres. This s. consists of a single lamella of perineurium covered on both surfaces by endothelium. It may inclose but a single nerve-fibre, in which case there is a space (lymph space) between it and the neurilemma of the nerve A, ape; A, at: A. ah: A 4, all; Ch. chin; Ch2, loch (Scottish); [s. 480]