CARTILAGE. 



53 



t. a certain extent resemble tendon-cells, but may be distinguished from them by 

 being surrounded by an investing capsule and by their being less flattened (Fig. 24). 

 The fibro-cartilages admit of 

 arrangement into four groups 

 interarticular, connecting, 

 circumferential, and strati- 

 form. 



The interarticular fibro-car- 

 tilages (msni'st'-i} are flattened 



FIG. 24. White fibro-cartilage from the semiluuar disk of the 

 patella joint of an ox. Magnified 100 times. 



nisei) are 



fibre-cartilaginous plates, of a 

 round, oval, triangular, or 

 sickle-like form, interposed 

 between the articular carti- 

 lages of certain joints. They 

 are free on both surfaces, thin- 

 ner toward their centre than 

 at their circumference, and 

 held in position by their mar- 

 gins and extremities being con- 

 nected to the surrounding ligaments. The synovial membrane of the joint is 

 prolonged over them a short distance from their attached margins. They are 

 found in the temporo-maxillary, sterno-clavicular, acromio-clavicular, wrist and 

 knee-joints. These cartilages are usually found in those joints which are most 

 exposed to violent concussion and subject to frequent movement. Their use is 

 to maintain the apposition of the opposed surfaces in their various motions ; to 

 increase the depth of the articular surfaces and give ease to the gliding movement ; 

 to moderate the effects of great pressure and deaden the intensity of the shocks to 

 which the parts mav be subjected. Humphry has pointed out that these inter- 

 articular fibro-cartilages serve an important purpose in increasing the variety of 

 movements in a joint. Thus, in the knee-joint there are two kinds of motion, 

 viz. angular movement and rotation, although it is a hinge joint, in which, as 

 a rule, only one variety of motion is permitted ; the former movement taking 

 place between the condyles of the femur and the interarticular cartilage, the latter 

 between the cartilage and the head of the tibia. So, also, in the temporo-maxil- 

 lary joint, the upward and downward movement of opening and shutting the 

 mouth takes place between the cartilage and the jaw-bone, the grinding move- 

 ment between the glenoid cavity and the cartilage, the latter moving with the 

 jaw-bone. 



The connecting fibro-cartilages are interposed between the bony surfaces of 

 those joints which admit of only slight mobility, as between the bodies of the ver- 

 tebra? and between the pubic bones. They form disks, which adhere closely to 

 both of the opposed bones, and are composed of concentric rings of fibrous tissue, 

 with cartilaginous laminae interposed, the former tissue predominating toward the 

 circumference, the latter toward the centre. 



The circumferential fibro-cartilages consist of a rim of fibro-cartilage, which 

 surrounds the margin of some of the articular cavities, as the cotyloid cavity of 

 the hip and the glenoid cavity of the shoulder ; they serve to deepen the articular 

 surface and to protect the edges of the bone. 



The stratiform fibro-cartilages are those which form a thin coating to osseous 

 grooves through which the tendons of certain muscles glide. Small masses of 

 fibro-cartilage are also developed in the tendons of some muscles, where they 

 glide over bones, as in the tendons of the peroneus longus and the tibialis 

 posticus. 



Yellow, or reticular, elastic cartilage is found in the human body in the 

 auricle of the external ear, the Eustachian tubes, the cornicula laryngis. and the 

 epiglottis. It consists of cartilage-cells and a matrix, the latter being pervaded 

 in every direction, except immediately around each cell, by a network of yellow 



