The development of the human body; a manual of human embryology . portion of the transverse andspinous processes; a double center (see p. 178) gives riseto the body of the vertebra; and each rib ossifies from asingle center. These various centers appear early in em-bryonic life, but the complete transformation of the car-tilages into bone does not occur until some time afterbirth, each vertebra at that period consisting of threeparts, a centrum and two halves of an arch, separated byunossified cartilage (Fig. 94, A). At about puberty secon- THE VERTEBRA. 187 dary centers make their appearance;
The development of the human body; a manual of human embryology . portion of the transverse andspinous processes; a double center (see p. 178) gives riseto the body of the vertebra; and each rib ossifies from asingle center. These various centers appear early in em-bryonic life, but the complete transformation of the car-tilages into bone does not occur until some time afterbirth, each vertebra at that period consisting of threeparts, a centrum and two halves of an arch, separated byunossified cartilage (Fig. 94, A). At about puberty secon- THE VERTEBRA. 187 dary centers make their appearance; one appears in thecartilage which still covers the anterior and posterior sur-faces of the vertebral centra, producing disks of bone inthese situations, another appears at the tip of each spinousand transverse process (Fig. 94, B), and in the lumbarvertebrae others appear at the tips of the articulatingprocesses. The epiphyses so formed remain separateuntil growth is completed and between the sixteenth andtwenty-fifth years unite with the bones formed from the. Fig. 95.—A, Upper Surface of the First Sacral Vertebra, and B,Ventral View of the Sacrum showing Primary Centers ofOssification. c. Centrum; na, neural arch; r, rib center.—(Sappey.) primary centers, which have fused by this time, to forma single vertebra. Each rib ossifies from a single primary center situatednear the angle, secondary centers appearing for the capit-ulum and tuberosity. In some of the vertebrae modifications of this typicalmode of ossification occur. Thus, in the upper five cervi-cal vertebrae the centers for the rudimentary ribs are sup-pressed, ossification extending into them from the neural 188 THE DEVELOPMENT OF THE HUMAN BODY. arch centers, and a similar suppression of the costal cen-ters occurs in the lower lumbar vertebra, the first onlydeveloping a separate rib center. Furthermore, in theatlas a double center appears in the persisting hypo-chordal bar, and the centrum which corresponds to
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
