36 CARTILAGES AND THEIR STRUCTURE. 



portion required, if its object only was that of nourishing the 

 bones. 



Its purpose in this animal, besides being a deposit of aliment 

 in reserve, is believed to be that of buoying up its head to ena- 

 ble it to respire with greater freedom. 



Cartilages and their Structure. 



CARTILAGES are white elastic substances, much softer than 

 bones, in consequence of a smaller quantity of earth entering 

 into their composition. 



Their structure is not so evidently fibrous as that of bones ; 

 yet by long maceration, or by tearing them asunder, a fibrous 

 disposition is perceptible. 



In articular cartilages their fibres are parallel to each other, 

 and directed towards the cavities of the respective joints. 



Their vessels are extremely small, though they can be readily 

 injected in cartilages where bone is beginning to form. The 

 vessels of the cartilages of the joints, however, seem entirely to 

 exclude the red blood ; no anatomist having yet been able to 

 inject them. They have no cancelli, nor internal membranes, 

 for lodging marrow ; no nerves can be traced into them ; nor do 

 they possess any sensibility in the sound state. 



Upon their surface, there is a thin membrane termed peri- 

 chondrium, which in cartilages supplying the place of bone, as 

 in those of the ribs or at the ends of long bones in children, is 

 a continuation of the periosteum, and serves the same general 

 purposes to cartilage as this does to bone. 



Upon the surface of articular cartilages, the perichondrium is 

 a reflection of the inner surface of the capsular ligament, and is 

 so very thin, and adheres so closely, as to appear like part of 

 the cartilage itself.* 



One set of cartilages supplies the place of bone, and by their 

 flexibility admit of a certain degree of motion, while their 



* The articular cartilages are the only ones not provided with a fibrous peri- 

 chondrium. The synovial membrane which is supposed to cover them by being 

 reflected from the inner face of the capsular ligament, is said to supply the place 

 of perichondrium. p. 



