78 CARTILAGE. 



ELASTIC OB YELLOW CARTILAGE. 



The epiglottis and cornicula of the larynx, the cartilages of the ear 

 and of the Eustachian tube, differ so much from the foregoing, both in 

 intimate structure and outward characters, that they have been included 



in a class apart, under the name of 

 Fig. 47. the "elastic," "yellow," or "spongy" 



cartilages. These are opaque and some- 

 what 3'ellow, are more flexible and tough 

 '^ )!<(if , than the ordinary cartilages, and have 



little tendency to ossify. They are made 

 up of cells and a matrix, but the latter 

 is everywhere pervaded with fibres (fig. 

 47), except sometimes in a little area 

 or narrow zone left round each of the 

 cells. These fibres resist the action of 

 acetic acid ; they are in most parts 

 short, straight, and confusedly intersect- 

 ing each other in all directions, like 

 Fig. 47.-SECTION OF THE Epi- ^| fiiauients in a piece of felt ; in such 



GLOTTIS, MAGNIFIED 3S0 DIAME- , • i i t 



TERs (Daly). parts the matrix has a rough mdis- 



tinctly granular look. Here and there the 

 filjres are longer and more fasciculated, but still interlace at short dis- 

 tances. In thin sections the cells readily drop out from the matrix, 

 leaving empty the cavities which they occupied. 



In the foetus the matrix of elastic cartilage is at fii-st homogeneous and hyaline, 

 and the elastic fibres are subsequently produced in it. They appear first in those 

 parts of the matrix which are in immediate connection with the cartilage-cells 

 (Hertwig. Deutschmann). In the cartilage of the external ear this change occurs 

 about the fifth month of intra-uterine life, and is .said to commence in the more 

 central parts, i.e., those furthest from the perichonckium (Rabl-Riickhard.) 



"WHITE riBRO-CARTILAGE. 



This is a substance consisting of a mixture of the fibrous and carti- 

 laginous tissues, and so far partaking of the qualities of both. Like 

 hyaline cartilage, it possesses firmness and elasticity, but these pro- 

 perties are united with a much greater degree of flexibility and tough- 

 ness. It presents itself under various forms, which may be enumerated 

 under the following heads. 



1. Intcrarticular fibro-cartilages. These are interposed between the 

 moving surfaces of bones, or rather of articular cartilages, in several 

 of the joints. They serve to maintain the apposition of the opposed 

 surfiiccs in their various motions, to give ease to the gliding movement, 

 and to moderate the effects of great pressure. In the jr)int of the lower 

 jaw and in that of the clavicle they have the form of round or oval 

 plates, growing thinner towards their centre ; in the knee-joint they 

 are curved in form of a sickle, and thinned away towards their concave 

 free edge. In all cases their surfaces are free ; while they are fixed by 

 synovial or fibrous membrane at their circumference or extremities. 

 The synovial membrane of the joint is prolonged for a short distance 

 upon these fibro-cartilagcs, from their attached margin. 



