37 



BUFFERS AND GLIDING SURFACES. 



Bones are the solid frame-work of the whole body and pos- 

 sess but little elasticity. 



These supporting and moving structures being also in sec- 

 tions and destined to move freely upon the ends of each other, 

 would have been peculiarly liable to concussion, and their 

 moving surfaces susceptible to attrition but for the interven- 

 tion of a substance of such a nature that would fully meet both 

 requirements. Such a substance we have in articular cartilage. 

 It combines those properties in the most eminent degree, that 

 break the violence of concussion, and by its extremely smooth 

 and glass-like surface, with the aid of the synovial fluid as a 

 lubricator enables the moving surfaces to glide on each other 

 with the greatest facility. Its anti-concussive functions may 

 be likened to those of the buffers upon the different sections of 

 a railway train ; while its free-gliding purposes may be fitly 

 illustrated by those of the smooth portions of the axle trees 

 upon which the train moves. 



ARTICULAR CARTILAGE; REMARKABLE CHARACTERISTICS. 



It is remarkable too, that no nerves or blood-vessels are 

 found in articular cartilage, while they are found in all other 

 kinds of cartilage. Why is this ? Because it would be incom- 

 patible with the exercise of its functions if it possessed either 

 sensibility or vascularity. In the former case, every jar or 

 quick movement would be necessarily attended by pain ; and 

 in the latter the vessels would be liable to rupture and extra- 

 vasation of their contents, when the weight of the animal was 

 thrown upon these structures. 



As nutrition and decay are necessary and constant processes, 

 the nutrient blood-vessels that supply these cartilages approach 

 them as closely as possible at their base from the interior of 

 the bone to which they belong, not terminating in the cartilage, 

 but abutting against their base by large numbers of small loops, 

 the cartilage having the property of imbibing their nutrient 

 particles from mere contact with the circular terminations of 



