40 HAND-BOOK OF PHYSIOLOGY. 



of an onion, arranged round each cell or group of cells. It is thus 

 shown to consist of nothing but a number of large systems of capsules 

 which have become fused with one another 



The cavities in the matrix in which the cells lie are connected to- 

 gether by a series of branching canals, very much resembling those in the 

 cornea: through these canals fluids may make their way into the depths 

 of the tissue. 



In the hyaline cartilage of the ribs, the cells are mostly larger than in 

 the articular variety, and there is a tendency to the development of fibres 

 in the matrix. The costal cartilages also frequently become calcified in 

 old age, as also do some of those of the larynx. Fat-globules may .also be 

 seen in many cartilages. 



In articular cartilage the cells are smaller, and arranged vertically in 

 narrow lines like strings of beads. 



Temporary Cartilage. In the foetus, cartilage is the material of 

 which the bones are first constructed; the "model" of each bone being 

 laid down, so to speak, in this substance. In such cases the cartilage is 

 termed temporary. It closely resembles the ordinary hyaline kind; the 

 cells, however, are not grouped together after the fashion just described, 

 but are more uniformly distributed throughout the matrix. 



A variety of temporary hyaline cartilage which has scarcely any matrix 

 is found in the human subject only in early foetal life, when it constitutes 

 the chorda dorsalis. 



Nutrition of Cartilage. Hyaline cartilage is reckoned among the 

 so-called non-vascular structures, no blood-vessels being supplied directly 

 to its own substance; it is nourished by those of the bone beneath. 

 When hyaline cartilage is in thicker masses, as in the case of the cartilages 

 of the ribs, a few blood-vessels traverse its substance. The distinction, 

 howeyer, between all so-called vascular and non-vascular parts, is at the 

 best a very artificial one. 



2. Yellow Elastic Cartilage. 



Distribution. In the external ear, in the epiglottis and cornicula 

 laryngis, and in the Eustachian tube. 



Structure. The cells are rounded or oval, with well-marked nuclei 

 and nucleoli (Fig. 41). The matrix in which they are seated is composed 

 almost entirely of fine elastic fibres, which form an intricate interlace- 

 ment about the cells, and in their general characters are allied to the yel- 

 low variety of fibrous tissue: a small and variable quantity of hyaline in- 

 tercellular substance is also usually present. 



A variety of elastic cartilage, sometimes called cellular, may be obtained 

 from the external ear of rats, mice, or other small mammals. It is com- 

 posed almost entirely of cells (hence the name), which are packed very 

 closely, with little or no matrix. When present the matrix consists of 



