46 



THE ESSENTIALS OF HISTOLOGY 



(fig. 54). Near the circumference, and under the perichondrium or 

 fibrous covering of the cartilage, they are flattened and parallel to the 

 surface, but in the deeper parts they have a more irregular or a radi- 

 ated arrangement. They frequently contain fat. The cartilages of the 

 larynx and windpipe and of the nose resemble on the whole the costal 

 cartilages, but the study of them may be deferred until the organs 

 where they occur are dealt with. 



Elastic or yellow fibro-cartilage occurs in only a few situations. 

 These are, the cartilage of the external ear and that of the Eustachian 

 tube, the epiglottis and cartilages of Santorini of the larynx, and in 

 some animals, e.g. the ox, the upper third of the arytenoids. The 

 matrix is everywhere pervaded with well-defined branching fibres, 

 which unite with one another to form a close network (fig. 55). These 



41 



FIG. 55. SECTION OF THE ELASTIC CARTI- 

 LAGE ov THE EAR. (Highly magnified.) 



FIG. 56. SECTION OF PART OF THE CAR- 

 TILAGE OF THE EPIGLOTTIS. 



a, cartilage-cell in clear area; b, granular- 

 looking matrix near the middle of the carti- 

 lage, 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. 



fibres resist the action of acetic acid, and are stained deeply by magenta; 

 they are evidently elastic fibres. In the ox they are very large, but 

 smaller in man, especially in the cartilage of the epiglottis (fig. 56). 

 They appear to be developed by the deposition of granules of elastiii 

 in the matrix, which at first lie singly, but afterwards become joined to 

 form the fibres. 



White fibre-cartilage is found wherever great strength combined 

 with a certain amount of rigidity is required : thus we frequently find 

 fibro-cartilage joining bones together, as in the case of the intervertebral 

 disks and other symphyses. Fibro-cartilage is frequently employed to 

 line grooves in which tendons run, and may also be found in the tendons 

 themselves. It is also employed to deepen cup- shaped articular sur- 

 faces ; and in the case of the interarticular cartilages, such as those 

 of the knee and lower jaw, to allow greater freedom of movement 

 whilst diminishing the liability to dislocation. Under the microscope 



