THE CARTILAGE. 1093 



network of very fine fibres, in other cases apparently destitute of any intercellular 

 substance. This is found in the external ear of rats, mice, and some other 

 animals, and is present in the chorda dorsalis of the human embryo, but is not 

 found in any other human structure. The various cartilages in the body are also 

 classified, according to their function and position, into articular, interarticular, 

 costal, and rnembraniform. 



Hyaline cartilage, which may be taken as the type of this tissue, consists of a 

 gristly mass of a firm consistence, but of considerable elasticity and of a pearly- 

 bluish color. Except where it coats the articular ends of bones, it is covered 

 externally by a fibrous membrane, the perichondrium, from the vessels of which it 

 imbibes its nutritive fluids, being destitute of blood-vessels. It contains no nerves. 

 Its intimate structure is very simple. 

 If a thin slice is examined under the 

 microscope, it will be found to consist 

 of a rounded or bluntly angular for in, 

 lying in groups of two or more in a 

 granular or almost homogeneous matrix 

 (Fig. 620). The cells, when arranged 

 in groups of two or more, have gener- 

 ally a straight outline where they are 

 in contact with each other, and in the 

 rest of their circumference are rounded. 

 The cell-contents consist of clear trans- C artFi^"o uman cartila e e - cells from the cricoid 

 lucent protoplasm, in which fine inter- 

 lacing filaments and minute granules may sometimes be seen ; imbedded in this 

 are one or two round nuclei, having the usual intranuclear network. The cells are 

 imbedded in cavities in the matrix, called cartilage lacunce ; around these the 

 matrix is arranged in concentric lines, as if it had been formed in successive por- 

 tions around the cartilage-cells. This constitutes the so-called capsule of the 

 space. Each lacuna is generally occupied by a single cell, but during the division 

 of the cells it may contain two, four, or eight cartilage-cells. By exposure to the 

 action of an electric shock the cell assumes a jagged outline and shrinks away 

 from the interior of the capsule. 



The matrix is transparent and apparently without structure, or else presents 

 a dimly granular appearance, like ground glass. Some observers have shown 

 that the matrix of hyaline cartilage, and especially the articular variety, after 

 prolonged maceration, can be broken up into fine fibrils. These fibrils are proba- 

 bly of the same nature, chemically, as the white fibres of connective tissue. It 

 is believed by some histologists that the matrix is permeated by a number of 

 fine channels, which connect the lacunae with each other, and that these canals 

 communicate with the lymphatics of the perichondrium, and thus the structure is 

 permeated with a current of nutrient fluid. This, however, is somewhat doubtful. 



Articular cartilage, costal cartilage, and temporary cartilage are all of the 

 hyaline variety. They present minute differences in the size and shape of their 

 cells and in the arrangement of their matrix. In articular cartilage, which shows 

 no tendency to ossification, the matrix is finely granular under a high power ; the 

 cells and nuclei are small, and are disposed parallel to the surface in the superficial 

 part, while nearer to the bone they become vertical. Articular cartilages have a 

 tendency to split in a vertical direction ; in disease this tendency becomes very 

 manifest. Articular cartilage is not covered by perichondrium, on its free surface, 

 where it is exposed to friction, though a layer of connective tissue can be traced 

 in the adult over a small part of its circumference continuous with that of the 

 synovial membrane, and here the cartilage-cells are more or less branched and pass 

 insensibly into the branched connective-tissue corpuscles of the synovial membrane. 



Articular cartilage forms a thin incrustation upon the joint-surfaces of the 

 bones, and its elasticity enables it to break the force of any concussion, while its 

 smoothness affords ease and freedom of movement. It varies in thickness accord- 



