CARTILAGE, commonly called Gristle, a substance intermediate in density between the membranous and bony structures of the body. It is distinguished from every other texture by its pearly whiteness, its smoothness, its firmness, and its great elasticity. When divided it appears to be perfectly homogeneous, without fibres and without lamina; ; but when examined under the microscope it is seen to consist of nucleated cells, disseminated in a solid mass or matrix. Articular Cartilage has no blood-vessels, the nutrient fluid required being supplied from vessels in adjoining textures. In other kinds of cartilagecanals are observed conducting blood, but not for the immediate supply of the cartilaginous tissue. No nerves have been found in any of the cartilages, and they are now known to be desti tute of sensibility.
The simplest form of Cartilage consists merely of nucleated cells, and closely resembles the cellular tissue of plants. This kind is found in the rudimentary spinal column of the early embryo ; it also exist. in the ehorda dorsalis of the cartilaginous fishes. In other kinds of cartilage the cells are embedded in an intercellular subetanee, presenting certain varieties of appearance.
In .Articular Cartilage the cells are oval or roundish, dispersed in groups through a nearly homogeneous intercellular substance. The cells measure from the 1300th to the 900th of an inch in diameter. In the Interior part of the incrusting cartilages the cells usually assume a more or less linear arrangement. In the different cartilages tho cells vary In size and form.
Ordinary permanent cartilage contains about three-fifths of its weight of water and becomes transparent when dried. It is resolved into chondrin by boiling. Cartilage contains a certain amount of mineral matters. Frornmherz and Gugert obtained 3.4 per cent. of ashes. When analysed these ashes were found to consist of— Carbonate of Soda . . . . 35'07 Sulphate of Soda . 24'24 Chloride of Sodium 8•`23 Phosphate of Soda . 0'92 Sulphate of Potash P20 Carbonate of Limo . 18'37 Phosphate of Lime 4'08 Phosphate of Magnesia . . . . . 6'91 Oxide of Iron, and loss 1.00 The vital processes are carried on very slowly in cartilage. It is subject to absorption, and when thus removed by disease or when taken away by operation it is not again renewed. When fractured or broken the union is not effected by new cartilage, but by fibrous or areolar tissue, or bone.
Cartilage is not only closely allied to bone in the mechanical arrangement of its component fibres and in its chemical composition, but it sometimes supplies the place of bono, as iu the fectus and in young persons. Cartilages of this class, which regularly disappear as
ossification advances, are called Temporary, in contradistinction to the Permanent, which remain during all perioda of life. Permanent Cartilages either cover the extremities of the bones in the moveable joints or articulations, and are thence, called Articular; or are attached to the extremities of the ribs, and are thence termed CostaL The Articular Cartilage consists of a layer of the same shape as the extremity of the bone which it covers, varying in thickness from one or two lines to the fraction of a line, and over its external or free surface there is always reflected a fine and delicate membrane, termed the synovial, which secretes the fluid by which the joint is lubricated and its free and easy motion secured, denominated synovia, or joint oiL The Costal Cartilages, which are cartilaginous productions of the osseous ribs, are much larger and thicker than the Articular, assist in the formation of the thoracic cavity, and perform a very important part in the function of respiration.
The distinctive property of this peculiar form of organised matter, to which the name of Cartilage has been given, is elasticity, on which depends the specific use of this substance in the economy. It is mainly an adjunct to bones, counteracting certain evils which, but for the intervention of some substance of this kind, must necessarily have resulted from the hard unyielding nature of the osseous fibres. Covering thee• extremities of bones, or interposed between layers of bony fibres, without in the least diminishing the firmness and strength of the osseous fibres, it enables the bones to yield in the shocks to which the body is exposed in the ever-varying movements of tho frame; defends them from fracture and displacement; and at the same time protects the great centres of the nervous system, the spinal cord and brain, from the concussions and jars to which these tender and delicate organs would, but for its interposition, have been constantly exposed.
(Quoin's Elements of Anatomy, by Sharpey ; Carpenter, Principles of Physiology; Simon, Animal Chemistry ; Schwann, On (he Accordance in (he Structure of Animals and Plants ; Kolliker, Ilandbuch der Gewebekhre.)