248 



ELASTIC OR YELLOW CARTILAGE. 



circumference ; but this arrangement is not constant, and they often appear quite 

 irregular. The cells, with the exception of those lying upon the surface, frequently 

 contain drops of oil, the nucleus being often altogether concealed by the fat The 

 matrix is clear, except where fibres have been developed in it, in which parts it is 

 opaque and yellowish. Such fibrous patches are very frequent ; the fibres are fine, 

 straight, and parallel, appearing transparent when few together. Besides these fibrous 

 patches in the interior of the rib-cartilages, the subperichondral layer is also pervaded 

 by bundles of fibres which are directly prolonged from the fibre-bundles of the peri- 

 chondrium and gradually lose themselves in the cartilage-matrix. There is in fact 

 no sharp line of demarcation between the perichondrium and the subjacent cartilage, 

 the one tissue passing by imperceptible gradation into the other. There is indeed 

 reason to believe that the superficial layers of the cartilage are formed by a trans- 

 formation of the fibrous tissue of the perichondrium during the growth of cartilage. 

 It is not uncommon to find the rib-cartilages extensively ossified. 



The description given of the microscopic characters of the costal cartilages will 

 apply with little variation to the ensiform cartilage of the sternum, to the cartilages 

 of the larynx and windpipe, except the epiglottis and cornicula laryngis, and to the 

 cartilages of the nose. With the exception of the last, these resemble the rib- 

 cartilages also in their tendency to ossify. 



The characters of the temporary cartilages, which are hyaline, will be noticed in 

 the account of the formation of bone. 



ELASTIC OR 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 

 the "elastic," "yellow," or "spongy" cartilages. These are opaque and somewhat 



Fig. 290. SECTION OF THE ELASTIC CARTILAGE OF THE EAR. HIGHLY MAGNIFIED (Hertwig). 



Fig. 291. SECTION OF PART OF THE CARTILAGE OF THE EPIGLOTTIS (Ranvier). 



a, cartilage cell in clear area ; b, granular-looking matrix near the middle of the cartilage, the 

 granular appearance being due partly to the fine reticulum of elastic fibres, partly to the presence of 

 granules of elastic substance in the matrix ; c, clearer matrix with longer fibres. 



yellow, are more flexible and tough than the ordinary cartilages, and have little 

 tendency to ossify. They are made up of cells and a matrix, but the latter is every- 

 where pervaded with fibres (fig. 290), except in a small area or narrow zone left round 

 each of the cells. The fibres resist the action of acetic acid ; they are in many 

 parts short, fine, and confusedly intersecting each other in all directions, like the 



