260 



THK ARTICULATIONS, OR JOINTS 



The matrix varies in the different varieties of cartilage. In hyaline cartilage it is bluisl 

 or pearly in appearance, and under low magnification is apparently homogeneous; in the fibro 

 cartilage the matrix consists mainly of white fibrous tissue arranged in bundles of varying sizi 

 with islands of hyaline matrix and cartilage cells at intervals; the matrix of elastic cartilag' 

 is mainly yellow elastic tissue with islands of hyaline matrix and cartilage cells. 



.1. Hyaline cartilage is surrounded by its perichondrium, internal to which is found th 

 apparently homogeneous or slightly granular matrix. If the latter be examined by polarize* 

 light or be first treated with potassium hydrate, the fundamental fibrillae are discernible. Thj 

 fibrils form a meshwork that contains the hyaline substance and cells. 



In joints the hyaline cartilage is found as a thin layer covering the articular surfaces o 

 the bones concerned, and is here called articular cartilage. In this form the peripheral cell 

 are parallel to the surface; deeper in toward the bone the cells become arranged in rows a 

 right angles to the surface. The latter condition may account for the vertical splitting of articula 

 cartilage that occurs in certain diseases. 



Hyaline cartilage is also found in the costal, tracheal, bronchial, and most of the laryngea 

 cartilages. It tends to calcify and even ossify in old age, and upon boiling yields a substanc 

 called chondrin. 



The hyaline cartilage that covers the joint surfaces of the bones, by its elasticity enables i 

 to break the force of any concussion, while its smoothness affords ease and freedom of move 

 ment. It varies in thickness according to the shape of the articular surface on which it lie? 

 where this is convex the cartilage is thickest at the centre, where the greatest pressure is received 

 the reverse is the case on the concave articular surfaces. 



/ <* 



FIG. 213. Sections of cartilage. A. Hyaline cartilage, a. Fibrous layer of perichondrium. b. Geneti 

 layer of perichondrium. c. Youngest chondroblasts. d. Older chondroblasts. e. Capsule, /.cells, g. Lacuna 

 B. Elastic cartilage. C. Wnite fibrocartilage. (Radasch.) 



B. Fibrocartilage is surrounded by a perichondrium; its matrix differs from that of th 

 hyaline variety in consisting chiefly of white fibrous tissue arranged in bundles with little island 

 of hyaline substance and cells scattered here and there. It is found in the intra-articular cai 

 tilages, deepening joint cavities, and in the intervertebral disks. It is arranged in thre 

 groups (1) intra-articular, (2) connecting, and (3) circumferential. 



1. The articular fibrocartilages, or articular disks (menisci articulares), are flattened, fibre 

 cartilaginous plates, of a round, oval, triangular, or sickle-like form, interposed between th 

 articular cartilages of certain joints. They are free on both surfaces, thinner toward thei 

 centre than at their circumference, and held in position by the attachment of their margin 

 and extremities to the surrouneling ligaments. The synovia! membrane of the joint is prolongei 

 over them a short distance from their attached margins. They are found in the temporo 

 mandibular, sternoclavicular, acromioclavicular, wrist- and knee-joints. These cartilages ar 



