The development of the human body; a manual of human embryology . gethemselves in rows (Fig. 88) and the process of calci-fication extends into thetrabecular of matrix whichseparate these rows. Whilethese processes have beentaking place the mesen-chyme surrounding thecartilage has become con-verted into a periosteum(po), similar to that ofmembrane bone, and itsosteoblasts deposit a layerof bone (p) upon the sur-face of the cartilage. Thecartilage cells now disap-pear from the intervals be-tween the trabecular ofcalcified matrix, whichform a fine network intowhich masses of mesen-chyme (Fig. 89
The development of the human body; a manual of human embryology . gethemselves in rows (Fig. 88) and the process of calci-fication extends into thetrabecular of matrix whichseparate these rows. Whilethese processes have beentaking place the mesen-chyme surrounding thecartilage has become con-verted into a periosteum(po), similar to that ofmembrane bone, and itsosteoblasts deposit a layerof bone (p) upon the sur-face of the cartilage. Thecartilage cells now disap-pear from the intervals be-tween the trabecular ofcalcified matrix, whichform a fine network intowhich masses of mesen-chyme (Fig. 89, pi), con-taining blood-vessels and osteoblasts, here and there pen-etrate from the periosteum, after having broken throughthe layer of periosteal bone. These masses absorb portionsof the fine calcified network and so transform it into acoarse network, the meshes of which they occupy to formthe bone marrow (m), and the osteoblasts which they con-tain arrange themselves on the surface of the persistingtrabeculae and deposit layers of bone upon their wmm The Ossification Center More Highly Magni- c, Ossifying trabeculae; cc, cavity ofcartilage network; m, marrowcells; p, periosteal bone; pi, ir-ruption of periosteal tissue; po,periosteum.—(Szymonowicz.) I78 THE DEVELOPMENT OF THE HUMAN BODY. In the mean time the calcification of the cartilage matrixhas been extending, and as fast as the network of calcifiedtrabeculse is formed it is invaded by the mesenchyme,until finally the cartilage becomes entirely converted intoa mass of spongy bone enclosed within a layer of morecompact periosteal bone. As a rule, each cartilage bone is developed from a singlecenter of ossification, and when it is found that a bone ofthe skull, for instance, develops by several centers, it isto be regarded as formed by the fusion of several prima-rily distinct bones, a conclusion which may generally beconfirmed by a comparison of the bone in question withits homologues in th
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
