496 



CARTILAGE. 



two forms : 1, the articular, attached to bone, 

 and entering into the formation of joints ; 2, the 

 non-articular, forming canals more or less per- 

 fectly. 



I. The articular cartilages are called diar- 

 throdial, abducent, or of incrustation, when 

 they belong to the moveable articulations; 

 synarthrodial when connected with those very 

 limited in their motions, or the immoveable 

 articulations of some authors. We think it 

 unnecessary to do more than refer to these 

 cartilages here, as their characters will be found 

 fully described in the article ARTICULATION. 



II. The non-articular cartilages are usually 

 much more flexible than the articular. In some 

 cases they are attached to bones, and lengthen 

 them out, as the preceding class. Of this we 

 see examples in the nose, the auditory canal, 

 and the Eustachian tube. In other cases they 

 are insulated, forming the basis of distinct 

 organs, as the larynx, the trachea, the eyelids. 

 All the cartilages of this class have a well- 

 marked perichondrium.* Some of them, as 

 the epiglottis, the tarsal cartilages, and those of 

 the alae nasi, are so thin, so flexible, and assume 

 so much of a fibrous appearance from their 

 perichondrium, that Bichat placed them amongst 

 the fibre-cartilages ; but these last never have 

 perichondrium, and their fibrous texture is 

 distinctly independent of their investment, as 

 is easily seen without any preparation. (See 



FlBRO-CARTILAGE.) 



The structure of non-articular cartilage, like 

 the other forms, may, by protracted maceration, 

 be shown to be fibrous ; but the arrangement 

 of its fibres is different; they interlace a good 

 deal more. 



The physical properties of cartilages are such 

 as to fit them admirably for the functions which 

 they have to perform. They are solid, resisting, 

 and incapable of extension, that they may be 

 able to preserve the form of certain parts as 

 effectually as bone ; and they are flexible and 

 elastic, to enable them to yield in some degree, 

 and immediately to resume their original shape. 



Elasticity is the property most essential to 

 them, and on this their usefulness mainly de- 

 pends. Its existence is easily demonstrated. 

 If the blade of a knife be pressed into a diar- 

 throdial cartilage, the reaction of the displaced 

 fibres expels it with force ; and a piece of any 

 cartilage, if bent between the fingers, returns 

 with a spring to its former shape. The elastic 

 fibres of diarthrodial cartilage are so placed as 

 to receive impressions on their extremities ; 

 they yield a little to force, and only a little, 

 else the ligaments would be too much relaxed ; 

 but they yield enough to let the opposite sur- 

 faces accommodate themselves to each other, 

 and to deaden the shocks which would other- 

 wise have an injurious effect on the nervous 

 centre. In fact, these articular cartilages serve 

 as a series of springs between the ground and 

 the delicate organs which they support. The 



* If we except the capsule of the lens and the 

 posterior layer of the cornea, supposing these 

 structures to belong to the cartilaginous system. 

 See EYE. 



elasticity of the costal cartilages is obvious and 

 essential. They are subject to torsion in the 

 act of inspiration, and by their reaction become 

 an important agent in expiration. 



Differences depending upon age. Cartilages 

 are soft, transparent, and like jelly in the very 

 young foetus. Gradually, as the individual 

 advances to maturity, they become opaque, 

 white, firm, and elastic; and in the adult these 

 qualities are in their greatest perfection. In 

 old age they lose again their elasticity and 

 flexibility ; a yellowish colour takes the place of 

 their beautiful pearly white; they become dry 

 and brittle, and shew a great tendency to ossify. 



Organization. Cartilage appears at first 

 sight to be perfectly homogeneous throughout, 

 like a concrete jelly, not shewing any traces of 

 organization, nor exhibiting the least appear- 

 ance of vessels. But, as an attentive examina- 

 tion proved it to be fibrous, so we shall be able 

 to satisfy ourselves that it possesses an organi- 

 zation similar to other parts of the living sys- 

 tem. In healthy cartilage, it is true, no red 

 vessels can be demonstrated, neither can the 

 finest injection be made to penetrate it, nor 

 will madder used in food colour it. But dis- 

 ease sometimes shows red vessels ramifying 

 through its substance ;* and several other phe- 

 nomena lead us to the conviction that it is at 

 all times permeated with vessels, though they 

 may be too fine to admit the red globules. For 

 instance, we find cartilage assume a yellow 

 tinge in jaundice. If we slice off a bit, the dry 

 surface is soon moistened with a serous fluid, 

 which, doubtless, comes from its colourless 

 vessels. Exposed cartilages have been known 

 to granulate, which implies the existence of 

 vessels, and perhaps of cellular substance. And 

 we know that in the old and laborious there is 

 often not the least sign of wear, although the 

 enamel of the teeth be quite worn away. Where 

 a perichondrium is present, we may suppose 

 the vessels first ramify in it before they enter 

 the cartilage. Dr. William Hunter describes 

 the arrangement of the vessels which supply 

 diarthrodial cartilage to be very peculiar. lie 

 says, " All around the neck of the bone there 

 are a great number of arteries and veins which 

 ramify into smaller branches, and communicate 

 with one another by frequent anastomoses, like 

 those of the mesentery. This might be called 

 the circulus articuli vascnlosus, the vascular 

 border of the joint. The small branches divide 

 into still smaller ones upon the adjoining sur- 

 face, in their progress towards the centre of the 

 cartilage. We are seldom able to trace them 

 into its substance, because they terminate ab- 

 ruptly at the edge of the cartilage, like the 

 vessels of the albuginea oculi when they come 

 to the cornea.''f 



It does not appear that nerves or absorbents 

 have ever been traced into cartilages : but the 

 phenomena of disease, pain, ulceration, &c., 

 convince us that they are supplied with both. 

 Even in their healthy condition, though their 



* Brodie on Diseases of Joints, p. 183, third 

 edition. 



f Phil. Trans. 1743. 



