Operative surgery, for students and practitioners . 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)layers. The uppermost of these visceral arches, that concerned in CONGENITAL DEFORMITIES OF THE FACE. 163 the formation of the face, is the thickest. It extends forward, andin front, where it is narrower, unites in the middle line with itsfellow of the opposite side, to form the mandibular arch, which repre-sents the future lower
Operative surgery, for students and practitioners . 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)layers. The uppermost of these visceral arches, that concerned in CONGENITAL DEFORMITIES OF THE FACE. 163 the formation of the face, is the thickest. It extends forward, andin front, where it is narrower, unites in the middle line with itsfellow of the opposite side, to form the mandibular arch, which repre-sents the future lower jaw. The second arch is less prominent thanthe first, and as it passes forward is directed somewhat upward. Thissecond arch does not reach as far as the middle line. The third andfourth arches are still less prominent and still shorter. These lowerthree arches do not join with their fellows across the middle line infront, but are continued into the plate of tissue which forms the frontwall of the (schlund) pharynx. From above downward these arches. Fig. 80.—Sagittal Section of the Head End of an Embryo Twelve DaysOld. A, alimentary tube; FB, vesicle of the forebrain overriding the end ofthe alimentary tube; N, neural tube; NC, notochord; OP, oral plate (site offuture mouth), ?which ruptures during the fourth week. overlap and partially conceal each other; so that the third and fourth,especially the fourth, are almost entirely concealed by the first andsecond. The uppermost arch appears earliest. The appearance ofthese arches is the first indication that marks the commencement ofthe formation of the face. Owing to the progressive growth of the visceral arches, whichcauses a thickening of the parts that immediately adjoin the areaalready mentioned as the oral plate, and on account of the presenceof the prominent overhanging forebrain vesicle (neural tube) above,the oral plate becomes relatively depressed, and we have thus, inits stead, a distinct fossa, which is called the oral
Size: 1768px × 1414px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthormcgrathj, bookcentury1900, bookdecade1910, bookyear1913
