52 



GENERAL ANATOMY. 



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 their 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 is not covered by perichondrium, at least 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, whilst its 

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

 ing to the shape of the bone on which it lies ; where this is convex the cartilage 

 is thickest at the centre, where the greatest pressure is received ; and the reverse 

 is the case on the concave surfaces of the bones. Articular cartilage appears to 

 imbibe its nutriment partly from the vessels of the neighboring synovial mem- 

 brane, 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 form arches, and then return into the substance of the 

 bone. 



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

 tendency to fibrous striation, especially in old age (Fig. 23). These cartilages 



are also very prone to ossify. In the 

 thickest parts of the costal cartilages a 

 few large vascular channels may be 

 detected. This appears at first sight an 

 exception to the statement that cartilage 

 is a non-vascular tissue, but is not so 

 really, for the vessels give no branches to 

 the cartilage-substance itself, and the 

 channels may rather be looked upon as 

 involutions of the perichondrium. The 

 ensiform cartilage may be regarded as 

 one of the costal cartilages, and the 

 cartilages of the nose and of the larynx 

 and trachea resemble them in microscop- 

 ical characters, except the epiglottis and 

 cornicular laryngis, which are of the 

 reticular variety. 



The hyaline cartilages, especially in 

 adult and advanced life, are prone to 

 calcify that is to say, to have their 



FIG. 23. Costal cartilage from a man seventy-six 

 years of age, showing the development of fibrous 

 structure in the matrix. In several portions of the 

 specimen two or three generations of cells are seen 

 enclosed in a parent cell-wall. High power. 



matrix permeated by the salts of lime without any appearance of true bone. 

 The process of calcification occurs also and still more frequently, according to 

 Rollett, in such cartilages as those of the trachea, which are prone afterward to 

 conversion into true bone. 



White fibro-cartilage consists of a mixture of white fibrous tissue and cartilag- 

 inous tissue in various proportions ; it is to the first of these two constituents 

 that its flexibility and toughness are chiefly owing, and to the latter its elasticity. 

 When examined under the microscope it is found to be made up of fibrous con- 

 nective tissue arranged in bundles, with cartilage-cells between the bundles ; these 



