THE STRUCTURE OF THE ELEMENTARY TISSUES. 



53 



come calcified in old age, as also do some of those of the larynx. Fat- 

 globules may also be seen in many cartilages (fig. 55). 



In articular cartilage the cells are smaller and arranged vertically in 

 narrow lines like strings of beads. 



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 ma- 



Fig. 55, 



Fig. 56. 



Fig. 55. Costal cartilage from an adult dog, showing the fat globules iu the cartilage cells. 

 (Cadiat.) 



Fig. 56. Yellow elastic cartilage of the ear. Highly magnified. (Hertwig.) 



trix is found in the human subject and in the higher animals generally, 

 in early foetal life, when it constitutes the chorda dorsalis. 



Nutrition. 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, however, 

 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 in this variety of cartilage are rounded or oval, 

 with well-marked nuclei and nucleoli (fig. 56). The matrix in which 

 they are seated is composed almost entirely of fine elastic fibres, which 



