THE OSSEOUS SYSTEM. 289 



and having a length of 0'05 of a line, may be distinctly noticed in almost 

 every preparation. 



Fig. 123. 



The sacro-iliac synchondrosis is effected by means of a flattened layer 

 of cartilage, f-1 J- of a line in thickness, which is closely attached to the 

 articular surfaces of the corresponding bones, between which it is inter- 

 posed. The cartilage-cells close to the bone are flattened, with their 

 surfaces directed towards it, and present beautiful transitionary forms 

 into half and wholly isolated bone-cells, which exist on the border of the 

 bone. In the interior of this cartilaginous layer, according to Zaglas, 

 there is always a narrow cavity, which separates the cartilaginous layers 

 of the two bones completely, or almost completely, from each other. It 

 contains a synovia-like fluid, and is bounded by smooth and even walls, 

 which differ from the rest of the cartilaginous substance in their greater 

 hardness, as well as in their structure. The matrix of these cartila- 

 ginous layers, in the direction of the surface, is finely fibrous; the cells 

 are all of large size (as much as 0'035 of a line), with numerous secondary 

 cells and uncommonly thick walls, so that the cavities, even of the se- 

 condary cells, often appear extremely contracted ; but they do not exhi- 

 bit any distinct indication of pore-canals or calcareous deposit. 



The costal cartilages are invested by a strong perichondrium, composed 

 of connective tissue and numerous elastic elements, which commences at 

 the sternal end in connection with the synovial membrane there existing, 

 and at the other is continuous with the periosteum of the ribs. The 

 cartilage, which is in connection with this membrane by a roughened 

 surface, is of considerable firmness although elastic, pale, yellow, or in 

 thin sections, exhibiting a transparent blue tint, internally almost always, 



FIG. 123. Cartilaginous border, towards the cartilage of the symphysis in Man; a, carti- 

 lage cells with thickened walls; 6, the same undergoing ossification; c, cells nearly ossified, 

 with homogeneous walls free in the matrix of the cartilage ; d, similar cells with calcareous 

 granules: e, ossified cells at the border of the matrix of the bone containing calcareous gra- 

 nules, and half projecting from it. Magnified 350 diameters. 



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