BOXE. Ixxxvii 



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 nbro-cartilage. Small nodules of this tissue (sesamoid fibro- 

 cartilages) may also be developed in the substance 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, nbro-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 differs much in the different instances 

 above enumerated. In general the fibrous tissue very greatly predominates, 

 and in some cases, as in the iuterarticular laminse of the knee-joint, ifc 

 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 Mr. Toynbee,* are 

 confined to the parts that are fibrous. 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 vertebrae have been destroyed by disease. It has not much 

 tendency to ossify. 



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

 Mr. Toynbee concludes from his researches that the cartilaginous element is 

 relatively more abundant at early periods. 



BONE, OR OSSEOUS TISSUE. 



The bones are the principal organs of support, and the passive instruments 

 of locomotion. Connected together in the skeleton, they form a framework 

 of hard material, which affords attachment to the soft parts, maintains them 

 in their due position, and shelters such as are of delicate structure, giving 

 stability to the whole fabric, and preserving its shape ; and the different 

 pieces of the skeleton, being jointed moveably together, serve also as levers 

 for executing the movements of the body. 



While substantially consisting of hard matter, bones in the living body 

 are covered with periosteum and filled with marrow ; they are also pervaded 

 by vessels for their nutrition. 



External configuration. In their outward forms the bones present much 

 diversity, but have been reduced by anatomists to the following classes. 

 1. Long or cylindrical, such as the chief bones of the limbs. These consist 

 of a body or shaft, cylindrical or more frequently angular in shape, and two 

 ends or heads, as they are often called, which are usually much thicker than 

 the shaft. The heads, or ends, have smooth surfaces for articulation with 

 neighbouring bones. The shaft is hollow and filled with marrow, by which 



* Phil. Trans. 1841. 



