OSSIFICATION IN CONNECTIVE TISSUE. 



269 



is magnified about twelve diameters. The bone is formed in membrane as in the 

 human foetus, but a thin plate of cartilage rises up on its inside from the base of the 

 skull. The ossification, however, is decidedly unconnected with the cartilage, and 

 goes on in a membrane lying outside of it. 



When further examined with a higher magnifying power, the tissue or membrane 

 in which the ossification is proceeding, appears to be made up of fibres and granular 

 corpuscles, with a ground-substance between, and, in point of structure, may not 

 unaptly be compared to connective tissue in a certain stage of development. The 

 corpuscles are large and angular, and they are densely packed all over the area of 

 ossification, covering the bony spicula, and filling up their interstices. 



On observing more closely the points of the growing osseous rays at the circum- 

 ference of the bone, where they shoot out into the soft tissue, it will be seen that 

 the portion of them already calcified is granular and rather dark in appearance 

 (fig. 309), bat that this character is gradually lost as they are traced further out- 

 Fig. 308. PARIETAL BONE OF AN EMBRYO SHEEP. 

 SIZE OF THE EMBRYO 2^ INCHES. (Sharpey.) 



The small tipper figure represents the bone of 

 the natural size, the larger figure is magnified about 

 12 diameters. The curved line, a, b, marks the 

 height to which the subjacent cartilaginous lamella 

 extended. A few insulated particles of bone are 

 seen near the circumference, an appearance which 

 is quite common at this stage. 



wards in the membrane, in which they are 

 prolonged for a little way in form of soft 

 and pliant bundles of transparent fibres 

 (fig. 309, B, of). 



These are termed osteogenic fibres, the 

 soft transparent matter of which they are 

 composed being known as osteogenic sub- 

 stance, or simply as osteogen. They 

 exhibit faint fibrillation, and have been 

 compared to bundles of white connective 

 tissue fibres, with which, in some 

 situations, they appear to be continuous 

 (G-egenbaur). But although similar in 

 chemical composition, they are somewhat 



different from these in appearance, having a stiffer aspect and straighter course, 

 besides being less distinctly fibrillated. The fibres become calcified by the 

 deposition within them of earthyfsalts in the form of minute globules, which 

 produce a darkish granular opacity, until the interstices between the globules 

 also become calcified, and the minute globules becoming thus fused together, the 

 new bone again looks comparatively clear (fig. 309, B, I). 



As already stated the fibrils which compose the osteogenic fibres themselves, are, according 

 to v. Ebner, not calcified, but the calcification affects only the matrix which unites 

 them. 



The bundles of osteogenic fibres which prolong the bony spicules, generally 

 spread out from the end of each spicule so as to come in contact with those from 

 adjacent spicules. When this happens, the innermost or proximal fibres frequently 

 grow together (fig. 309, B, c), whilst the other fibres partially intercross as they 

 grow further into the membrane. The ossific process extends into the osteogenic 



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