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ARTICULATION. 



249 



b. Synarthrodial cartilage. The cartilages 

 synarthrodial articulations are destined in 

 some degree to act as bonds of union, as well 

 as means of separation and for the prevention 

 of the effects of concussion. They are simply 

 cartilaginous laminae interposed between the 

 osseous articular surfaces, very adherent to both, 

 and adherent likewise by their margins to the 

 periosteum or ligamentous expansions which 

 may pass from one bone to another. We find 

 instances of these cartilages in the sacro-iliac 

 symphysis, or synchondrosis, as it has been 

 called from the junction of the bones by carti- 

 lages;* also in the sutures, where there are 

 very thin cartilaginous laminae interposed be- 

 tween the osseous margins. These laminae 

 will be found to be triangular in their section, 

 the thin edge or apex being internal, which, as 

 Meckel observes, may in some degree account 

 for the earlier obliteration of the sutures on the 

 internal than on the external surface of the 

 cranium. These cartilages of sutures are not 

 strictly permanent ; they disappear with age : 

 and according to Beclard, hold the midway, as 

 to frequency of ossification, between permanent 

 and temporary cartilages.f 



The cartilages of the ribs perform in some 

 degree the office of articular cartilage ; they are 

 situated between two osseous surfaces ; they 

 form bonds of union, and their elasticity is 

 eminently essential to the full performance of 

 the movements of the thorax. 



In fishes most of the moveable articulations 

 are provided with elastic cartilages, which serve 

 the double purpose of forming bonds of union 

 as well as of permitting motion by their elasticity. 



3. Fibro-cartilage. This remarkable struc- 

 ture, called by the older anatomists ligamentous 

 cartilage or cartilaginiform ligament, is made 

 much use of in the articulations ; and it is well 

 adapted for a means of union, by reason of its 

 great strength, which it owes to its ligamentous 

 part, and of its elasticity, for which it is indebted 

 to its cartilaginous portion. We find fibro- 

 cartilage to be connected with the joints under 

 three forms : 



a. In the form of laminae, free on both sur- 

 faces to a greater or less extent, and lined to 

 the same extent by the synovial membrane re- 

 flected upon them. | These are the interarti- 



* No one can have failed to notice the peculiar 

 yellow appearance of the cartilage in the sacro- 

 iliac articulation. Does that arise from an admix- 

 ture of the yellow elastic tissue with the pure carti- 

 lage, by which the elasticity of the latter is in- 

 creased ? 



t It is doubted by some whether these cartilagi- 

 nous laminje can be admitted into the class of arti- 

 cular cartilages; they being regarded as forming a 

 nidus for the extension of the flat cranial bones, 

 and the sutures being supposed to be useful only for 

 this purpose, viz. to admit of the growth of these 

 bones at their margins in a manner analogous to 

 that of long bones at their extremities. See Soem- 

 merring de Corp. Hum. Fab. t. i. p. 212, and Gibson 

 on the use of sutures in the skulls of animals, 

 Manchester Memoirs, 2d series, vol. i. 



t This point, however, is liable to the same 

 objections as that of the continuity of the synovial 

 membrane over diaithrodial articular cartilages, 

 which will be considered in a subsequent part of the 

 article. 



cular cartilages or menisci of authors. They 

 are found in the temporo-maxillary, sterno- 

 clavicular, and tibio-femoral articulations, some- 

 times in the acromio-clavicular, between the 

 bodies of the cervical vertebrae in birds, and in 

 general in those joints where there is constant 

 and extensive motion, and consequently where 

 the articular surfaces are exposed to consider- 

 able friction. The principal use of these fibro- 

 cartilaginous laminae must unquestionably be 

 to guaid against any bad consequences likely 

 to arise from this continued friction ; this is 

 particularly obvious in the sterno-clavicular 

 articulation. To increase the depth of an arti- 

 cular excavation is another object, as appears 

 from the semilunar cartilages of the knee-joint; 

 and moreover, in conjunction with the attain- 

 ment of these two objects, to ensure in all the 

 motions of the joint a perfect adaptation of the 

 articular surfaces to one another, as will appear 

 obvious to any one who carefully considers the 

 construction of the temporo-maxillary or even 

 of the knee-joint. 



It will be observed, that I do not include in 

 the class of interarticular fibro-cartilages, the 

 lamina which is commonly known by the name 

 of the triangular cartilage of the wrist joint, as is 

 done by all the systematic writers I have looked 

 into ; for, first, it does not appear to me to be 

 fibro-cartilaginous in its structure ; it is purely 

 cartilaginous ; and, secondly, it is not interar- 

 ticular, in the sense in which we here use that 

 term, viz., as lying between two articular surfaces. 

 This lamina seems to be merely an extension of 

 the cartilaginous incrustation of the inferior ex- 

 tremity of the radius, which completes the ar- 

 ticular surface for the reception of the first row 

 of carpal bones. The scaphoides and lunare are 

 provided for by the radius; but as the ulna 

 could not be brought into the composition of 

 the wrist-joint without interfering with the 

 motions of the inferior radio-ulnar articulation, a 

 structure such as the triangular cartilage, was 

 necessary one which would present a sufficient 

 opposing surface to the articular portion of the 

 os cuneiforme, and which would not impede or 

 obstruct the necessary motions of the joint 

 between the radius and ulna. 



In the cases of the temporo-maxillary and 

 sterno-clavicular articulations, these fibro-carti- 

 lages form, in general, complete septa between 

 two portions of the joint : so that there are then 

 two synovial sacs; but sometimes there is a per- 

 foration in the centre of the fibro-cartilage. 



b. The second class of articular fibro-carti- 

 lages consists of those which Meckel designates 

 fibro-cartilages of circumference, or cylindrical 

 fibro-cartilages. They form fibro-cartilaginous 

 brims to certain articular excavations; they are 

 triangular in their section, attached by their 

 basis to the osseous margin of the articular 

 cavity, and free at their apices, lined by synovial 

 membrane on the whole of one side, and a 

 great part of the other. They are to be found 

 only in two joints, namely, on the margin of 

 the acetabulum in the hip-joint, and on the 

 edge of the glenoid cavity in the articulation of 

 the shoulder ; in the former, this fibro-cartilage 

 is much larger and stronger, and is evidently 



