The development of the human body; a manual of human embryology . and fifth sacral vertebra?. As devel-opment proceeds a rotation of the cartilage, accompaniedby a slight shifting of position, occurs, so that eventually the plate has its long axisalmost parallel with thevertebral column and isin relation with the firstthree sacrals. Ossifica-tion appears at threepoints in each cartilage,one in the upper part toform the ilium (Fig. 109,il) and two in the lowerpart, the anterior of thesegiving rise to the pubis(p), while the posteriorproduces the ischium(is). At birth thesethree bones are still
The development of the human body; a manual of human embryology . and fifth sacral vertebra?. As devel-opment proceeds a rotation of the cartilage, accompaniedby a slight shifting of position, occurs, so that eventually the plate has its long axisalmost parallel with thevertebral column and isin relation with the firstthree sacrals. Ossifica-tion appears at threepoints in each cartilage,one in the upper part toform the ilium (Fig. 109,il) and two in the lowerpart, the anterior of thesegiving rise to the pubis(p), while the posteriorproduces the ischium(is). At birth thesethree bones are still sep-arated from one an-other by a Y-shapedpiece of cartilage whosethree limbs meet at thebottom of the acetabu-lum, but later a secondary center appears in this carti-lage and unites the three bones together. The centralpart of the lower half of each original cartilage plate doesnot undergo complete chondrification, but remains mem-branous, constituting the obturator membrane whichcloses the obturator foramen. In addition to the Y-shaped secondary center, other. Fig. 109.—The Ossification Centers of the os , b, c, and d, Secondary centers for the crest, anterior inferior spine of symphysis, and ischial tuberosity; il, ilium; is, ischium; p, pubis.— (Testut.) THE PELVIC GIRDLE AND LOWER LIMB SKELETON. 211 epiphysial centers appear in the prominent portions of thecartilage, such as the pubic crest (Fig. 109, c), the ischialtuberosity (d), the anterior inferior spine (b) and the crestof the ilium (a), and unite with the rest of the bone atabout the twentieth year. The femur, tibia, and fibula each develop from a singleprimary center for the shaft and an upper and a lowerepiphysial center, the femur possessing, in addition, epi-physial centers for the greater and lesser trochanters(Fig. 90). The patella does not belong to the same cate-gory as the other bones, but resembles the pisiform boneof the carpus in being a sesamoid bone developed in thetendon of the quadri
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
