Operative surgery, for students and practitioners . Face.—About the twelfth day thearrangement of the head end of the embryo is quite simple. A cross-section shows it to consist of two tubes, one being situated in frontof the other. The anterior is the blind, head end of the alimentarytube,—the future pharynx. The posterior is the enlarged neural tubewhich is later developed into the brain. The anterior wall of this 163 HEAD AND FACE. Tipper^ head end of the alimentan^ tube is called the oral plate/and marks the location of the future mouth and face. A sagittalsection will also show this relat
Operative surgery, for students and practitioners . Face.—About the twelfth day thearrangement of the head end of the embryo is quite simple. A cross-section shows it to consist of two tubes, one being situated in frontof the other. The anterior is the blind, head end of the alimentarytube,—the future pharynx. The posterior is the enlarged neural tubewhich is later developed into the brain. The anterior wall of this 163 HEAD AND FACE. Tipper^ head end of the alimentan^ tube is called the oral plate/and marks the location of the future mouth and face. A sagittalsection will also show this relationship, and further that the neuraltube not only lies behind the alimentary tube, but also arches for-ward above the upper end of the latter like a hood, overriding itanteriorly. This upper part of the neural tube, which projects forwardover the end of the alimentary tube, is called the vesicle of the fore-brain. In the third week there may be seen, upon either side of thehead end of the embryo, four transverse plates or ribs of tissue which. Fig. 79.—Transverse Section of the Head End of an Embryo Twelve Days , alimentary tube; 2V^, neural tube; NC, notochord; OP, oral plate. are separated from one another by deep fissures, or clefts. Thethickened plates are called visceral arches, and the intervening spaces,or fissures, visceral clefts. Within the alimentary tube, upon itsinner aspect, there may be seen corresponding arches and clefts. Thesearches are simply thickenings or ribs in the lateral walls of the headend (scJilund pharynx) of the alimentary tube. Each mass con-sists of mesoblast, covered upon its outer surface by the epidermiclayer, which covers the whole exterior of the body, and upon itsinner surface by the endodermic layer, which lines the whole innersurface of the alimentary tube. Between the arches, at the bottomof any two opposed clefts, the wall of tissue is extremely thin; consistspractically of the outer (epidermic) and the inner (endodermic)laye
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Keywords: ., bookauthormcgrathj, bookcentury1900, bookdecade1910, bookyear1913
