. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. i56 DEVELOPMENT OF BONE po pi C ^;. into a coarse network, the meshes of which they occupy to form the bone maigow (m), and the osteoblasts which they contain arrange themselves on the surface of the persisting trabeculse and deposit layers of bone upon their surfaces. In the meantime the calcifica- tion of the cartilage matrix has been extending, and as fast as the network of calcified trabeculse is formed it is invaded by the mesen- chyme, until finally the cartilage becomes entirely conver
. The development of the human body : a manual of human embryology. Embryology; Embryo, Non-Mammalian. i56 DEVELOPMENT OF BONE po pi C ^;. into a coarse network, the meshes of which they occupy to form the bone maigow (m), and the osteoblasts which they contain arrange themselves on the surface of the persisting trabeculse and deposit layers of bone upon their surfaces. In the meantime the calcifica- tion of the cartilage matrix has been extending, and as fast as the network of calcified trabeculse is formed it is invaded by the mesen- chyme, until finally the cartilage becomes entirely converted into a mass of spongy bone enclosed within a layer of more compact periosteal bone. As a rule, each cartilage bone is developed from a single center of ossification, and when it is found that a bone of the skull, for in- stance, develops by several cen- ters, it is to be regarded as formed by the fusion of several primarily distinct bones, a conclusion which may generally be confirmed by a comparison of the bone in ques- tion with its homologues in the lower vertebrates. Exceptions to this rule occur in bones situated in the median line of the body, these occasionally developing from two centers lying one on either side of the median line, but such centers are usually to be regarded as a double center rather than as two distinct centers, and are merely an expression of the fundamental bilaterality which exists even in median structures. More striking exceptions are to be found in the long bones in which one or both extremities develop from special centers which give rise to the epiphyses (Fig. 94, ep, ep'), the shaft or diaphysis (d) being formed from the primary center. Similar secondary centers appear in marked prominences on bones to which powerful muscles Fig. 93.—The Ossification Center of Fig. 92 More Highly Magnified. c, Ossifying trabeculse; cc, cavity of cartilage network; m, marrow cells; p, periosteal bone; pi, irruption of peri- osteal tissue; po, periosteum.
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Keywords: ., bookautho, bookcentury1900, bookdecade1910, booksubjectembryology
