. The science and practice of dental surgery. lete separation of the oral margin of theprimitive jaw to form the lips and gums givesrise to the condition known as atresia of thelips and gums, a rare malformation except inits slight forms, in which it occurs in associationwith a complete hare-lip. A thick fraenumlabii is a less marked degree of this mandible at an early period consistsentirely of Meckels cartilage, embedded inembryonic tissue; at an earher .stage it con-sisted of mesoderm enclosed between the snrfaceectoderm and the entoderm of the fore-gut. theentire structure be
. The science and practice of dental surgery. lete separation of the oral margin of theprimitive jaw to form the lips and gums givesrise to the condition known as atresia of thelips and gums, a rare malformation except inits slight forms, in which it occurs in associationwith a complete hare-lip. A thick fraenumlabii is a less marked degree of this mandible at an early period consistsentirely of Meckels cartilage, embedded inembryonic tissue; at an earher .stage it con-sisted of mesoderm enclosed between the snrfaceectoderm and the entoderm of the fore-gut. theentire structure being known as a visceral arch(see Fig. 1(5). Growing into each of the fivevisceral arches is an artery (visceral arch 6 vessel) arising from the truncus arteriosus ofthe primitive heart (see Fig. 10). The visceralarch vessel supplying the first and secondarches is derived from the external carotidartery. The nerve of supply to the first visceralarch {i. e. the mandibular nerve) is derived fromthe first cephalic ganghon,a segment of the neural. Fig. 10.—Hiiman embryo of about three weeks,showing the visceral arclies and clefts (after Quain). S, StomatodEieum; O, Olfactory depression; CV,Cerebral vesicles; H, Heart; TA, Truncus arteri-osus ; A^, Aortic branch of first visceral arch;VC, Visceral cleft (first); OV, Otic vesicle; JV,Jugular vein; CV, Cardinal vein; DC, Duct ofCuvier; W, Vitelline vein ; UV, tjmbUical vein;UA, Umbilical artery; All, Allantois; P, Placenta;PS, Primitive mesodermal somite; nf, Naso-frontalprocess; »i. Maxillary process; md, Mandibularprocess. crest or ectodermic tliickening of the medullarygroove, the earliest representative of a centralnervous system in the embryo (see Figs. 6, 7). The mcsodermic tissue of the visceral archesbecomes differentiated into connective tissue,and this constitutes the membranous stage of theJaw, the remaining mesoderroic tissue forming the muscular and connective tissues around thejaw (see Fig. 17). Cartilage develops in e
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectdentistry, bookyear19
