The development of the human body; a manual of human embryology . y processwhich grows forward and ventrally to form the anteriorboundary of the mouth, while the remaining portion of thearch forms the mandibular process. Cartilage appears inthe posterior or dorsal part of each maxillary process, andthe rod so formed applies itself by its ventral end to the under surface of thesphenoid region ofthe chondrocranium,forming the cartilagi-nous internal ptery-goid plate. The wholeof the axis of themandibular process,on the other hand,becomes chondrified,forming a rod knownas Meckels cartilage,and th
The development of the human body; a manual of human embryology . y processwhich grows forward and ventrally to form the anteriorboundary of the mouth, while the remaining portion of thearch forms the mandibular process. Cartilage appears inthe posterior or dorsal part of each maxillary process, andthe rod so formed applies itself by its ventral end to the under surface of thesphenoid region ofthe chondrocranium,forming the cartilagi-nous internal ptery-goid plate. The wholeof the axis of themandibular process,on the other hand,becomes chondrified,forming a rod knownas Meckels cartilage,and this, at its dorsalend, comes into relation with the periotic capsule, asdoes also the dorsal end of the cartilage of the secondarch. In the remaining three arches cartilage formsonly in the ventral portions, so that their rods do notcome into relation with the skull, though it will be con-venient to consider their further history together withthat of the other branchial arch cartilages. The ar-rangement of these cartilages is shown diagrammatic-ally in Fig. Fig. 100.—Diagram showing the FiveBranchial Cartilages, / to V. I1, Internal pterygoid process of the sphe-noid; At, atlas; Ax, axis; 3, third cervi-cal vertebra. THE SKULL. 195 By the ossification of these various parts three catego-ries of bones are formed: (i) cartilage bones formed inthe chondrocranium, (2) membrane bones, and (3) car-tilage bones developing from the cartilages of the bran-chial arches. The bones belonging to each of these cat-egories are primarily quite distinct from one another andfrom those of the other groups, but in the human skull avery considerable amount of fusion of the primary bonestakes place, and elements belonging to two or even to allthree categories may unite to form a single bone of theadult skull. In a certain region of the chondrocraniumalso and in one of the branchial arches the original carti-lage bone becomes ensheathed by membrane bone andeventually disappears completely, so
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectembryol, bookyear1902
