42 GENERAL ANATOMY. 



Cartilage is divided according to its minute anatomy into true or hyaline 

 cartilage, fibrous, or fibro- cartilage, and yellow, or elastic, or reticular cartilage. 

 The various cartilages in the body are also classified according to their function 

 and position, into articular, interarticular, costal, and membraniform. 



True Cartilage, which may be taken as the type of this tissue, consists of a 

 gristly mass, of a pearly bluish color, enveloped in a fibrous membrane, the 



perichondrium, from the vessels of 



Flg ' 13 ' which it imbibes its nutritive fluids, 



being itself destitute of bloodvessels ; 

 nor have nerves been traced into it. 

 Its intimate structure is very simple. 

 If a thin slice be examined under 

 QV. the microscope, it will be found to 

 ^H consist of cells of a rounded or an- 

 gular shape, with nucleus and nucleo- 



lus, lying in groups, surrounded by 



a granular or almost homogeneous 



Human cartilage cells, from the cricoid cartilage. ' . _.,... .. 



(Magnified 350 times.) matrix. By boiling the cartilage 



for some hours, and treating it with 



acetic acid, the cell membrane which lines the cavity in the matrix may be 

 made visible. The matrix is often arranged in the form of a concentric ring 

 around the cartilage-cell, forming what is described by some authors as the . 

 cartilage-capsule. 



The articular cartilages, the temporary cartilages, and the costal cartilages, 

 are all of the hyaline variety. They present minute differences in the size and 

 shape of their cells, and in the arrangement of the matrix. In the articular 

 cartilages, which show 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, 

 probably from some peculiarity in the intimate structure, or arrangement of the 

 component parts, of the matrix. In disease this tendency to a fibrous splitting 

 becomes very manifest. Articular cartilage in the adult is not covered by peri- 

 chondrium, at least on its free surface, where it is exposed to friction, though an 

 epithelial layer can be traced in the foetus over the whole surface of the car- 

 tilage, and in the adult over a small part of its circumference, continuous with 

 the epithelium of the synovial membrane. This is probably the remains of an 

 investing membrane which is worn away in after-life by the action of the joint. 

 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, whilst 

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

 according to the shape of the bone on which it lies ; where this is convex, the 

 cartilage is thickest over the convexity where the greatest pressure is received, 

 and the reverse is the case in the concavities of the joints. Articular cartilage 

 appears to imbibe its nutriment partly from the vessels of the neighboring 

 synovial membrane, partly from those of the bone upon which it is implanted. 

 Mr. Toynbee has shown that the minute vessels of the cancellous tissue, as 

 they approach the articular lamella, dilate, and, forming arches, return into the 

 substances of the bone. 



Temporary cartilage, and the process of its ossification, will be described 

 with bone. 



In the costal cartilages the colls and nuclei are large, and the matrix has a 

 tendency to fibrous striation, especially in old age. These cartilages also are 

 very prone to ossify. In the thickest parts of the costal cartilages a few large 

 va.-i-iilar channels may be detected. This appears at first sight an exception to 

 the statement that cartilage is a non- vascular tissue, but it is not so really, for 

 the vessels give no branches to the cartilage-substance itself, and the channels 



