SYNO VIAL MEMBRANE and FLUID (from Neo-Lat. synorialis, from synovia, lubri cating fluid secreted by a synovial membrane, so called because it resembles the white of an egg, from Gk. syn, together + Lat. ovum, egg). In every joint in which a considerable range of motion is required, the osseous segments (or contiguous extremities of bones) are sep arated by a space, which is called the cavity of the joint. The end of each of the bones enter ing into the composition of the joint is incrusted by a layer of articular cartilage adapted to its form, and the entire cavity of the joint is lined by a delicate membrane, which is termed the swim:qui membrane, which secretes a peculiar viscid matter, termed synoria, or synorial for the purpose of lubricating the inner surface. Being a serous membrane a synovial membrane is always a closed bag, like the pleura, for ex ample, with an attached and a free surface, the latter being smooth and moist. The minute structure of a synovial membrane is much the same as that of serous membranes elsewhere.
(See HisTotocy.) A very simple form of syno vial membrane—anatomically known as a bursa —is employed to facilitate the gliding of a tendon of a muscle or of the integument over a projec tion of hone. It consists of a bag connected by areolar tissue with the neighboring parts, and secreting a fluid in its interior. These bags are sometimes prolonged into synorial sheaths, which surround long tendons, such as those of the flexor and extensor muscles of the fingers and toes. In felon (q.v.), when inflammation extends to one of the sheaths, and gives rise to the forma tion of the motion of the inclosed tendon is destroyed, and a permanently stiff fin ger is the result. See SYNOVITIS.
The synorial fluid, or synoria, consists of water holding in solution mucin, albumen, fat, and inorganic salts. Excessive movement diminishes its amonnt, makes it more inspissated, and in creases the numb], but diminishes the salts.