The development of the human body; a manual of human embryology . n to the fusion of two or some-times four centers of ossification, appearing in the mem-branous roof of the embryonic skull. The bone so formed(ip) interparietal of lower vertebrates and, at an early stage, uniteswith the supraoccipital,although even at birthan indication of the lineof union of the two partsis to be seen in two deepincisions at the sides ofthe bone. The union ofthe exoccipitals and su-praoccipital takes placein the course of the firstor second year afterbirth, but the basioccipi-tal does not fuse
The development of the human body; a manual of human embryology . n to the fusion of two or some-times four centers of ossification, appearing in the mem-branous roof of the embryonic skull. The bone so formed(ip) interparietal of lower vertebrates and, at an early stage, uniteswith the supraoccipital,although even at birthan indication of the lineof union of the two partsis to be seen in two deepincisions at the sides ofthe bone. The union ofthe exoccipitals and su-praoccipital takes placein the course of the firstor second year afterbirth, but the basioccipi-tal does not fuse withthe rest of the bone untilthe sixth or eighth will be noticed thatno special centers occurfor the four occipital ver-tebrae, these structures having become completely incor-porated in the chondrocranium, and even the cartilagi-nous partitions which divide the anterior condyloid for-amen usually disappear during the process of the sphenoidal region the number of distinct boneswhich develop is much greater than in the occipital Fig. 101.—Occipitai, Bone of a Fetus at Term. bo, Basioccipital; eo, exoccipital; ip, interparietal; so, supraoccipital. THE SKULL. 197 In the first place, the basal portion of the cartilage ossifiesto form two bones, an anterior or presphenoid and a poste-rior or basisphenoid (Fig. 102, b), and on each side of eachof these an ossification appears giving rise to two lesserwings or orbito sphenoids (os) and two greater wings oralisphenoids (as), and an additional center appears oneach side of the basisphenoid to form the lingula (I). Inthe course of the third month the lingular fuse with thebasisphenoid, the orbitosphenoids unite with the pre-sphenoid at about the sixth month, and a little later thepresphenoid and basisphenoid unite, the fusion of thealisphenoids with the basisphenoids not taking place untilafter birth. The centers which give rise to the alisphe-
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
