The development of the human body; a manual of human embryology . 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
The development of the human body; a manual of human embryology . 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-. Fig. 102.—Sphenoid Bone from Embryo op 3J to 4 parts which are still cartilaginous are represented in black, as,Alisphenoid; b, basisphenoid; /, lingula; os, orbitosphenoid; p,internal pterygoid plate.—(Sappey.) noids extend into the external pterygoid plates, but theinternal plates (p) are formed by membrane bone whichencloses and eventually replaces the pterygoid cartilagederived from the first branchial arch. It seems probablethat the upper anterior angle of the alisphenoids arisesfrom a special ossification developing in membrane in thisregion. The cartilage of the ethmoidal region of the chondro-cranium forms somewhat later than the other portionsand consists at first of a stout median mass projectingdownward and forward into the fronto-nasal process (Tig. 198 THE DEVELOPMENT OF THE HUMAN BODY. 103. lp) afld two lateral masses (Im), situated one on eitherside in the mesenchyme on the outer side of each olfactorypit. Ossification of the lateral masses or ectethmoids
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
