248 ARTICULATION 



a. Diarthrodial cartilage. The general small circular dimples wliere the little bundles 



characters of this class of articular cartilage of the cartilaginous fibres were fixed. Thus 



may be best examined on the articulating ex- we may compare the texture of a cartilage to 



tremities of the long bones. Here we observe the pile of velvet, its fibres rising up from the 



it moulded exactly to the forms of those sur- bone, as the silky threads of that rise from the 



faces, insomuch that, after a little maceration, woven cloth or basis. In both substances the 



the cartilage may, by careful dissection, be short threads sink, and bend in waves upon 



removed from the bone, to which it adheres being compressed, but by the power of elasti- 



with great firmness, and will be found to ex- city recover their perpendicular bearing as 



hibit an exact mould of the articular ex- soon as they are no longer subjected to a 



tremity ; hence these cartilages have been called compressing force. If another comparison 



" cartilages of incrustation. 1 ' This cartilage was necessary, we might instance the flower 



is perfectly distinct at the early periods of life of any corymbiferous plant, where the Jiosculi 



from the temporary cartilage which forms the and stamina represent the little bundles of 



nidus of the future bone, and cannot be re- cartilaginous fibres, and the calyx, upon which 



garded as a portion of that cartilage left un- they are planted, bears analogy to the bone."* 



ossified ; this may easily be seen by examining The total absence of vessels capable of car- 



a vertical section of a femur or tibia at this rying red blood in articular cartilage is proved 



period ; and the peculiar arrangement of the by the failure of even the minutest injections to 



fibres of the articular cartilage, hereafter to be pass into the cartilage, and a further confirma- 



noticed, constitutes an additional proof that it tion of this opinion is derived from the fact 



is completely distinct from that which is after- that madder taken into the system of a young 



wards transformed into bone. animal does not stain them. The attempts of 



The physical properties and general charac- anatomists to trace lymphatics and nerves into 

 ters of this form of cartilage do not differ from this structure have been equally unavailing, 

 those of the others ; it possesses the same The design of articular cartilages, as means 

 pearly whiteness the same apparent homoge- to break the violence of shocks, is well illus- 

 neousness of structure the same elasticity the trated by comparing the different arrangement 

 same absence of vessels carrying red blood. It of the cartilaginous incrustation on convex arti- 

 is not covered by a perichondrium ; the surface cular surfaces from that on concave. In the 

 towards the joint is peculiarly smooth and glis- former, we observe the layer of cartilage to be 

 tening, and is generally supposed to owe these very thin at the circumference of the articular 

 properties to its being lined by a layer of the surface, its thickest portion being in the centre, 

 synovial sac of the joint ; this point, however, while the opposite arrangement obtains on con- 

 has been controverted, as we shall notice in a cave surfaces : there the thinnest portion of the 

 subsequent part of the article. The first and cartilage is in the centre, and the layer increases 

 the most complete investigation of the true in thickness as it approaches the circumference, 

 anatomical construction of articular cartilage " The articulating cartilages are most hap- 

 was that announced by Dr. William Hunter so pily contrived to all purposes of motion in 

 long ago as 1743.* His paper still deserves those parts. By their uniform surface they 

 the most attentive perusal, not only for the move upon one another with ease : by their 

 actual information it affords on its professed soft, smooth, and slippery surface mutual abra- 

 subject, but as a specimen of the careful and sion is prevented : by their flexibility, the con- 

 original method of observation pursued by its tiguous surfaces are constantly adapted to each 

 distinguished author. To examine the structure other, and the friction diffused equally over the 

 of articular cartilages, it is necessary to subject whole : by their elasticity, the violence of any 

 them to boiling or along-continued maceration.f shock, which may happen in running, jumping, 



" When an articulating cartilage is well pre- &c. is broken and gradually spent ; which 

 pared," says Dr. Hunter, " it feels soft, yields must have been extremely pernicious, if the 

 to the touch, but restores itself to its former hard surfaces of bones had been immediately 

 equality of surface when the pressure is taken contiguous. As the course of the cartilaginous 

 off. This surface, when viewed through a fibres appears calculated chiefly for this last 

 glass, appears like a piece of velvet. If we advantage, to illustrate it, we need only reflect 

 endeavour to peel the cartilage off in lamellae, on the soft undulatory motion of coaches, which 

 we find it impracticable, but if we use a certain mechanics want to procure by springs, or upon 

 degree of force, it separates from the bone in the difference betwixt riding a chamber-horse 

 small parcels, and we never find the edge of and a real one."f 

 the remaining part oblique, but always perpen- 

 dicular to the subjacent surface of the bone. * Loc. cit. p. 516. 



If we view this edge through a glass, it appears t Hunter, in loco citato. Hunter's account of 



like the edge of velvet, a mass of short and articular cartilage is completely confirmed by M. 



nearly paraUel Bbres rising from the bone, and %%?, In 178^^1^ 



terminating at the external surface of the carti- cart iiage as " une multitude des petits filets adosses 



lage : and the bone itself is planned out into et lies les uns aux autres tous perpendiculaires au 



plan de 1'os, en un mot parfaitement semblables 



* Of the Structure and Diseases of Articular par leur structure, ou par leur position a. la substance 



Cartilage, Phil. Trans, vol. xlii. emaillee des dents, laquelle n'est composec, comme 



t The articular cartilage on the patella may be on sait, que de filets osseux, poses perpendiculake- 



selected as very favourable for this purpose. See ment sur le corps de la dent : la comparaison est 



the plate annexed to W. Hunter's paper. des plus exactes." 



