BONE. 79 



2. The articular cavities of bones are sometimes deepened and ex- 

 tended by means of a rim or border of fibro-cartilage. A good example 

 of one of these circumferential or mari/incil fibro-eartilages is seen in the 

 hip-joint, attached round the lip of the cotyloid cavity. 



3. Conncctitui fibro-cartilages are such as pasr> between the adjacent 

 surfaces of bones in joints which do not admit of gliding motion, as at 

 the symphysis of the pubes and between the bodies of the vertebrae. 

 They have the general form of disks, and are composed of concentric 

 rings of fibrous tissue with cartilage interposed ; the former itredomi- 

 nating at the circumference, the latter increasing towards the centre. 

 The bony surfaces between which they pass are usually encrusted with 

 true cartilage. The modifications which they present in particular 

 instances are described in the special anatomy of the joints. 



4. The bony grooves in which tendons of muscles glide are lined with 

 a thin layer of fibro-cartilage. Small nodules of this tissue {scscimoid 

 fihro-carfUcujes) may also be developed in the suljstance of tendons, of 

 which there is an example in the tendon of the tibialis posticus, where 

 it passes beneath the head of the astragalus. Lastly, fil)ro-cartilage is 

 sometimes connected with muscular tissue, and gives attachment to 

 muscular fibres, like that which is known to exist at the orifices of the 

 heart. 



Fibro-cartilage appears under the microscope to be made up of 

 bundles of fibres, like those of ordinary ligament, with cartilage-cells 

 intermixed ; but the proportion of the two elements diflFers much in 

 the difterent instances above enumerated. In general the fibrous tissue 

 very greatly predominates, and in some cases, as in the interarticular 

 laminaj of the knee-joint, it constitutes almost the entire structure. In 

 the intervertebral disks the cartilage-corpuscles are abundant towards 

 the centre of the mass where the cartilaginous tissue prevails, and the 

 substance is softer. 



In chemical composition this texture agrees most with ligament, 

 yielding gelatin when boiled. 



Its blood-vessels are very few, and, according to Toynbee,* are con- 

 fined to the parts that arc fil)rous. Its vital changes are slow ; it is 

 subject to absorption, but much less readily so than bone ; hence it is no 

 uncommon thing to find the intervertebral disks entire when the 

 adjacent bodies of the vertebras have been destroyed by disease. It 

 has not much tendency to ossify. 



Little is known concerning the mode of development of fibro-cartilage. 

 It is probable that the matrix is at first hyaline and that fibrous tissue 

 is subsequently developed within it, but whether as an ingrowth from 

 the perichondrium or not is not known with certainty. 



BONE OR OSSEOUS TISSUE. 



The bones are the principal organs of su]iport, and the passive in- 

 struments of locomotion. Connected together in the skeleton, they 

 form a framework of hard material, whicli afibrds attachment to the 

 soft parts, maintains them in their due position, and shelters suc-h as 

 are of delicate structure, giving stability to the whole fabric, and pre- 

 serving its shape ; and the difterent pieces of the skeleton, being joined 



* riiil. Trans. ISil. 



