350 GENERAL ANATOMY. 



have a free surface, covered by the synovial membrane which 

 is closely attached to it, and a surface which also adheres in- 

 timately to the surface of the bone, without a continuity of 

 tissue however existing between them. Their circumference, 

 which is thinner than the rest, extends to that of the articular 

 surfaces of the bones. Their thickness, which is inconsidera- 

 ble and proportionate to their breadth, is from one to two 

 lines in the largest, and a fraction of a line in the smallest. 

 It is not the same in the whole of their extent. Those which 

 incrust or tip convex bony surfaces are thicker at the centre 

 than in the remainder of their extent. Those of the concave 

 surfaces, on the contrary, are thicker at the circumference 

 than at the centre. 



555. The texture of these cartilages is at first sight as in- 

 distinct as that of the others, so that they resemble a layer of 

 wax spread over the bone, but may be discovered by certain 

 modes of procedure, it is fibrous. Maceration of an articu- 

 lar part of a bone, continued for six months, effects the de- 

 struction of the synovial membrane, the only membrane co- 

 vering the cartilage which is destitute of the fibrous perichon- 

 drium, and produces disunion of the fibres of which it is 

 composed, which rise perpendicularly from the surface of the 

 bone like the pile of velvet. If a cartilage thus disposed by 

 maceration be dried, the fibres become smaller and thus sepa- 

 rate from each other, becoming more distinct. Decoction, 

 when not prolonged so as to dissolve the cartilage, produces 

 at first the same effect as maceration. The action of fire also 

 discloses the structure in the same manner. These cartilages 

 have no vessels. Delicate injection and microscopic inspec- 

 tion show the capillary vessels terminating at their circumfer- 

 ence and at their adherent surface, without ever penetrating 

 into their substance. 



These cartilages, which are compressible and elastic, deaden 

 the effects of pressure and concussions. The smoothness of 

 their surface facilitates the motion of the diarthrodial articula- 

 tions. They become much thinner in old age. 



556. In preternatural joints, no true cartilages are pro- 

 duced, but only desmo-chondroid tissue, a tissue which, in 



