. Anatomy, descriptive and applied. Anatomy. Fig. 34.—Development of the sacrum. Period of Development.—At about the eighth or ninth week of fetal life ossification of the central part of the bodies of the first three vertebrae commences, and between the fifth and eighth months in the last two. Between the and eighth months ossification of the lamina takes place; and at about the same period the centres for the lateral masses for the first three sacral vertebrfe make their appearance. The period at which the arch becomes completed by the junc- tion of the laminae with the bodies in fron
. Anatomy, descriptive and applied. Anatomy. Fig. 34.—Development of the sacrum. Period of Development.—At about the eighth or ninth week of fetal life ossification of the central part of the bodies of the first three vertebrae commences, and between the fifth and eighth months in the last two. Between the and eighth months ossification of the lamina takes place; and at about the same period the centres for the lateral masses for the first three sacral vertebrfe make their appearance. The period at which the arch becomes completed by the junc- tion of the laminae with the bodies in front and with each other behind varies in different segments. The junction between the laminae and the bodies takes place first in the lower vertebrae as early as the second year, but is not effected in the uppermost until the fifth or sixth year. About the sixteenth year the epiphyses for the upper and under surfaces of the bodies are formed, and between the eighteenth and twentieth years those for each lateral surface of the sacrum make their appearance. The bodies of the sacral vertebrae are, during early life, separated from each other by intervertebral disks. At about the eighteenth year the two lowest segments become joined by ossification extending through the disk. This process gradually extends upward until all the segments become united, and the bone is completely formed from the twenty-fifth to the thirtieth year of life. The coccyx is developed from four centres, one for each piece. Occasionally one of the first three pieces of this bone is developed from two centres, placed side by side. The ossific nuclei make their appearance in the following order: In the first segment, between the first and fourth years; in the second piece, at from five to ten years; in the third, from ten to fifteen years; inthe fourth from fourteen to twenty years. As age advances these various segments become^ united with each other from below upward, the union between the first and second
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1913
