THE OSSEOUS SYSTEM. 291 



sometimes more extensive. In the former case, it does not proceed 

 further than to the incrustation of the cartilage-cells, and of the matrix 

 in which they are lodged, which has become fibrous ; in the latter, and 

 frequently, also, in the former, the ossification is preceded by the forma- 

 tion of hollow spaces in the cartilage, in which is deposited a cartilage- 

 marrow, containing vessels, which are connected, in part with those of 

 the perichondrium, in part with those of the ribs ; and the osseous sub- 

 stance is more that of normal bone, though almost always more opaque, 

 less homogeneous, and with imperfectly formed lacunse, which frequently 

 contain a calcareous deposit. Under the name of cartilage-marrow, are 

 understood the medulla-cells, fat-cells, bundles of connective tissue and 

 vessels which are presented instead of the detritus, afforded by the dis- 

 integration of cartilage, and which may be said to correspond in all re- 

 spects with those of developing foetal bone, and may be readily observed 

 in ossifying costal and laryngeal cartilages. 



95. B. Movable Articulation (Diarthrosis). The articular extremi- 

 ties of the bones, or any other surfaces entering into the formation of a 

 joint, are invariably invested with a thin layer of cartilage, which in the 

 middle of the surfaces covered by it, is of tolerably uniform thickness, 

 gradually thinning as it extends outwardly, and finally terminating with 

 a very abrupt edge. This articular cartilage is closely applied to the 

 bone with a rough, hollowed or raised surface, but is not united to it by 

 any interposed substance ; and, on the opposite surface, it is in most joints 

 usually quite bare, and directed towards the cavity of the articulation. 

 Sometimes, however, it is invested with a special fibrous membrane, a 

 pericJiondrium, which is an immediate prolongation of the periosteum, 

 and extends most generally only over a small portion of the cartilage, 

 gradually ceasing without any defined margin.* In some joints (shoulder, 

 hip) the more secure lodgment of the articular head of the bone is in- 

 sured by special cartilaginous lips. These are firm, yellowish-white, 

 fibrous rings, attached, at the border of the articular cartilage, by a 

 wider basis, immediately to the bone or partly to the cartilage. They 

 thin off to an acute edge, and for the most part free and uncovered by 

 the synovial membrane, or any epithelium, project into the articulation, 

 being exteriorly in relation with the periosteum and synovial capsule. 



* [Reichert, who has paid particular attention to the question of the existence of an epi- 

 thelium upon the articular cartilages, says, that in the foetal condition of Man and the domes- 

 tic Mammalia, an epithelium exists over the whole surface of the synovial capsules, and, on 

 the articular cartilage, lies in immediate contact with its substance. It resembles the epi- 

 thelium of the vessels. In adults, on the other hand, he could discover an epithelium only 

 on those parts of the articular capsules which are not subject to friction ; and here it had the 

 same appearance as in the fcetal condition. It was wanting upon the articular cartilages and 

 their immediate neighborhood ; but it was not uncommon to meet with fine desquamated 

 flakes of cartilage in the synovia, which fell readily into folds, and thus resembled a fibro- 

 cartilaginous tissue (Bericht, Mailer's "Archiv.," 1849, p. 10.) TRS.] 



