80 HISTOLOGY 



trate the matrix of the cartilage. In some cases, however, vascular con- 

 nective tissue occupies an excavation in its peripheral portion. What- 

 ever nutriment the cells in the interior of the cartilage receive is obtained 

 by diffusion through the matrix. It has been asserted that this diffusion 

 takes place through a system of canals penetrating the matrix, and pass- 

 ing from one lacuna to another as in bone. But in mammalian carti- 

 lage the only canals which have been recorded are presumably the 

 result of shrinkage, such as may be produced by treating the specimen 

 with absolute alcohol or ether. 



The three principal forms of cartilage hyaline, elastic, and fibro- 

 cartilage and the exceptional "vesicular supporting tissue" may be 

 further described as follows: 



Hyaline cartilage, the commonest type, is characterized by its clear, 

 pale bluish or pearly translucent matrix, which is ordinarily free from 

 fibrils. The nasal cartilages, most of the laryngeal cartilages, and the 

 tracheal and bronchial rings are of this variety, together with the xiphoid 

 and costal cartilages, and the articular cartilages which cover the joint 

 surfaces of the bones. In embryos the greater portion of the skeleton 

 is at first formed of hyaline cartilage. Although the matrix usually ap- 

 pears homogeneous, it may be resolved into bundles of parallel fibers by 

 artificial digestion, and its behavior toward polarized light indicates an 

 underlying fibrillar structure. Sometimes, as a degenerative process, a 

 network of fibers may appear in the matrix, staining red with eosin, and 

 resembling the elastic fibers shown in Fig. 68, 3. Such a condition has 

 been observed in the trachea. In degenerating portions of the laryngeal 

 and costal cartilages, fibers having a luster like asbestos (or the mineral 

 amianthus) are sometimes seen; according to Prenant these "amianthoid 

 fibers" are neither white nor elastic. In old age a deposit of calcareous 

 granules often occurs in the matrix of hyaline cartilage, and in some of 

 the laryngeal cartilages this change may begin by the twentieth year. 

 With the increase and coalescence of the granules, the cartilage becomes 

 calcified, and blood vessels may enter it; but it does not form true bone. 

 As with other calcified structures, such as tendon, treatment with acids 

 shows that the underlying tissue has retained its characteristic features, 

 and remains quite different from bone. 



Elastic cartilage contains, in its matrix, granules, fibers or networks 

 of elastic substance (Figs. 67, B, and 68) ; consequently its color is yellowish. 

 It is found in the external ear, the auditory (Eustachian) tube, the epi- 

 glottis, and in certain small cartilages of the larynx, namely the cornicu- 

 late and cuneiform cartilages and the vocal processes of the arytsenoid 

 cartilages. It develops from hyaline cartilage, which it closely resembles. 

 Within its matrix, granules of elastic material are deposited, which 

 later coalesce to form fibers. Some authorities have stated that they 



