246 



HYALINE CARTILAGE. 



intensely blue colour) to mix with the circulating blood of animals, which after a time are 

 killed and the cartilages examined. Proceeding in this way, Gerlach was unable to see any 

 blue channels in the cartilage-matrix, while Arnold, on the other hand, obtained results from 

 which he was led to infer the existence of minute cleft-like spaces throughout the matrix, 

 connected by fine radiating canaliculi on the one hand with the lymphatics in the perichon- 

 drium, and on the other hand with the cell-spaces of the cartilage. 



Such is the structure of hyaline cartilage in general, but it is more or less modi- 

 fied in different situations. 



In articular cartilage, the matrix in a thin section appears dim, like ground 

 glass, having sometimes an almost granular aspect. The cells and cell-groups are 

 smaller and more dispersed, as a rule, than in rib-cartilage. As is the case also with 

 the cartilage of the ribs, the groups are flattened at and near to the surface, and lie 



Fig. 286. VERTICAL SECTION OF ARTICULAK CARTILAGE COVERING THE LOWER END OP THE TIBIA 

 (HUMAN). MAGNIFIED ABOUT 30 DIAMETERS. (E. A. S.) 



a, cells, and cell-groups flattened conformably with the surface ; 6, cell-groups irregularly arranged ; 

 c, cell-groups disposed perpendicularly to the surface ; d, layer of calcified cartilage ; e, bone. 



parallel with it (fig. 286, a) ; deeper and nearer the bone, on the other hand, they are 

 narrow and oblong, like short irregular strings of beads, and are mostly directed 

 vertically (fig. 286, c). It is well known that articular cartilages readily break in a 

 direction perpendicular to their surface, and the surface of the fracture appears to 

 the naked eye to be striated in the same direction, as if they had a columnar 

 structure ; this may be due to the vertical arrangement of the rows of cells, or to the 

 substance of the matrix being disposed in a fibrous or columnar manner (Leidy). 

 It was formerly held that the free surface of articular cartilage is covered with 

 epithelioid cells, but no such covering really exists. It is easy, no doubt, to peel off 

 a thin film from the surface of the cartilage of the head of the hurnerus or femur ; 

 but this superficial layer is really part .of the cartilage, and its broad patches of cells 

 with the intermediate matrix are not to be mistaken (fig. 287). 



Near the margin of the articular cartilages connective tissue is prolonged a 

 certain way into them from the periosteum and synovial membrane, and the cartilage- 

 cells acquire processes and present transitions to the connective-tissue corpuscles of 

 that membrane (fig. 288). There is no sharp demarcation between the two tissues, 

 which here pass continuously into one another. 



Except at this transitional zone the matrix of articular cartilage rarely 



