THE OSSEOUS SYSTEM. 



295 



increase in thickness, Cruveilhicv (" Diet, de M(^d. et Chir. prat." III., 

 514) having noticed fibres of this kind as much as G lines in length, thus 

 far exceeding the normal thickness of articular cartilage. They some- 

 times wear away rapidly, or even disappear altogether (in suppuration 

 in the bone or in the articulation), so that the surface of the bone is left 

 exposed; they also undergo partial loses of substance; when they 

 exhibit ulcerous excavations, which may penetrate to the bone, or com- 

 mence on the osteal surface of the cartilage. 



§ 96. The articular capsules [capsulce s. memhrance synoviales) are 

 not closed capsules, but short, wide tubular sacs, which are attached by 

 two open ends to the borders of the articular surfaces of the bones, and 

 thus connect them together. They are essentially more or less delicate, 

 transparent membranes, but are in many situations so closely and com- 

 pletely invested externally by fibrous layers — the fibrous capsules as they 

 are termed, — as on cursory inspection to present the aspect of tolerably 

 tough capsules. These fibrous coats are met with especially in situations 

 where the articulation is either wholly unprotected, or but thinly covered 

 by soft parts, or where a very firm connection is required (as in the hip- 

 joint); they are absent for the most part, or are undeveloped, where 

 muscles, tendons, and ligaments rest upon the articulation, or where, for 

 special purposes, the synovial membrane is exposed to more considerable 

 movements (as in the knee and elbow). 



The relation of the articular capsules to the bones and articular car- 

 tilages, more precisely described, is as follows (Fig. 126) : — The articular 

 capsule is attached, either simply to the border of 

 the cartilaginous surface, extending thence directly 

 to the other bone [patella, ampliiartliroses) ; or it 

 may, in the first place, besides the border of the 

 cartilage, also invest a larger or smaller extent of 

 surface of the bone itself, and then pass to the 

 second bone, with which it is connected in the one 

 way or the other. In either of these cases the 

 synovial membrane does not adhere immediately to 

 the hard tissues subjacent to it, but is more or less 

 closely connected with the periosteum and peri- 

 chondrium, ultimately ceasing without any distinct 

 margin, not far from the border of the articular cartilage, with the 

 perichondrium of which it is inseparably united. 



With respect to the intimate structure of these tissues, the synovial 



Fig. 12G. — Diagram of a transverse section of a phalangeal articulation, partly after 

 Arnokl : a, bones ; 6, articular cartilage; c, periosteum continuous with the pcrkhnnd rkan of 

 tlie articular cartilage; d, synovial inembrane at the edge of the cartilage, connected at first 

 with the perichondrium ; c, its epithelium. 



Fiff. 126. 



