44 



GENERAL ANATOMY. 



is to maintain the apposition of the opposed surfaces in their various motions-, 

 to increase the depth of the articular surface, and give ease to the gliding 

 movement ; to moderate the effects of great pressure, and deaden the intensity 

 of the shocks to which the parts may be submitted. Virchow describes in the 

 semilunar cartilages of the knee a system of anastomosing tubes, formed by 

 cells which communicate with each other, and by means of which the nutritious 

 fluids are conveyed into the interior of the mass. The semilunar disks, accord- 

 ing to this author, are wrongly denominated cartilages, since they yield no 

 chondrine on boiling ; and he appears to regard them as a modification of ten- 

 dinous structure, which, however, agrees with the cartilages in the important 

 particular of being non-vascular. (See Yirchow's "Cellular Pathology," by 

 Chance, pp. 87-89.) 



The connecting fibro-cartilages are interposed between the bony surfaces of those 

 joints which admit of only slight mobility, as between the bodies of the verte- 

 brae and the pubic symphyses ; they form disks, which adhere closely to both 

 of the opposed bones, and are composed of concentric rings of fibrous tissue, 

 with cartilaginous laminae interposed, the former tissue predominating towards 

 the circumference, the latter towards the centre. 



The circumferential fibro-cartilages consist of a rim of fibre-cartilage, which 

 surrounds the margin of some of the articular cavities, as the cotyloid cavity 

 of the hip, and the glenoid cavity of the shoulder ; they serve to deepen the 

 articular surface and to protect the edges of the bone. 



The stratiform fibro-cartilages are those which form a thin layer in the osseous 

 grooves, through which the tendons of certain muscles glide. 



Fis. 16. 



Yellow cartilage, ear of horse. (High power.) 



The Yellow or Reticular Cartilages found in the human body are the epiglot- 

 tis, cornicula laryngis, and the cartilaginous parts of the ear (auricle and 

 Eustachian tube). In this variety the cartilage cells lie in the meshes of a 

 network of yellow elastic fibres, with a double outline, branching and anasto- 

 mosing in all directions. The fibres resemble those of the yellow elastic 

 fibrous tissue, both in appearance and in being unaffected by acetic acid, and 

 according to Eollett their continuity with the elastic fibres of the neighboring 

 cellular tissue admits of being demonstrated. 



The distinguishing feature of cartilage as to its chemical composition is that 

 it yields on boiling a substance called chondrine, very similar to gelatine, but 

 differing from it in not being precipitated by tannin. 



