CARTILAGE. BONE. TEETH. 29 



tilages, those of the joints, the cartilages of the nose, 

 the thyroid, cricoid, and arytenoid cartilages, and 

 the cartilaginous rings of the trachea and bronchial 

 tubes. 



Fibro-cartilage differs from true cartilage only in 

 the nature of its fundamental substance or basis, 

 which, instead of being structureless, is fibrous. The 

 fibres of which it consists are of the elastic variety, at 

 least in most fibro-cartilages (PL V. fig. III). The 

 intervertebral discs and the semi-lunar cartilages of 

 the knee-joint we have found to be the only excep- 

 tions to this rule ; their fundamental substance con- 

 sisting almost entirely of connective fibres. 



The principal fibro-cartilages are those of the Distribution. 

 external ear and Eustachian tube, the epiglottis, the 

 little cartilaginous masses at the summits of the ary- 

 tenoid cartilages, the intervertebral discs, and inter- 

 articular cartilages. 



Cartilage, like all other tissues, is developed from Development, 

 embryonic cells. Those cells which are about to take 

 on the cartilaginous transformation, secrete from their 

 external surfaces an enveloping membrane, which 

 becomes their capsule, whilst a solid structureless 

 material is deposited around them, constituting the 

 fundamental substance. In the formation of fibro- 

 cartilage a portion only of the original formative cells 

 take on the changes above described, whilst the 

 remainder transform themselves into connective and 

 elastic fibres. 



The growth of cartilage is effected in part by the Growth. 

 endogenous multiplication of its cells (vide sect. 1, 

 chap. 1), and in part by the addition of new tissue to 



