Human anatomy, including structure and development and practical considerations . ,di the rectum by this method is distinctly danj^^erous fromthe risk oi laceration of the j.;;ut. It is therefore not in much favor. DEVELOPMENT OF THE ALIMENTARY TRACT. Reference to the cross-section of a young mammalian embryo (Fig. 1428) showsthe early relation between the primitive gut and the yolk-sac, of which latter theformer is evidently a part. The longitudinal section of a very young human embryo(FiJ. 46, page 39) emphasizes the wide communication between the two. ThedifTerentiation of the gut from the
Human anatomy, including structure and development and practical considerations . ,di the rectum by this method is distinctly danj^^erous fromthe risk oi laceration of the j.;;ut. It is therefore not in much favor. DEVELOPMENT OF THE ALIMENTARY TRACT. Reference to the cross-section of a young mammalian embryo (Fig. 1428) showsthe early relation between the primitive gut and the yolk-sac, of which latter theformer is evidently a part. The longitudinal section of a very young human embryo(FiJ. 46, page 39) emphasizes the wide communication between the two. ThedifTerentiation of the gut from the yolk-sac is accomplished by the approximationand union of the two splanchno|)leuric folds which consist of the entoblast internally,continuous with that of the yolk-sac, and the visceral layer of the mesoblast exter-nally. As the union of the splanchnoi)leur£e proceeds, the gut-tube becomes closed Fig 1428. Neural tube ,Mvotome Amniotic sac. Amnion. crif>rd // /?>iVvV*v-:.l*l^^P^^i^^!^^ U^Primitive Body-cavity-_!y A^^--^^r.^Av* >>4 *^ /•>4Vi \i Vitelline vein. f*^HV V Open gut-tube Visceral mesoblast Transverse section of early rabbit embryo, showing differentiating gut-tube still communicating with vitelline sac. X 80. throughout its cephalic and caudal segments, between which, however, it remainsopen and connected with the volk-sac by a communication that rapidly narrows andelongates into the vitelline or umbilical duct, a structure that for a considerable timeremains as a canal bearing the diminishing volk-sac or umbilical vesicle at its outerend. The primitive digestive tract, therefore, is closed both anteriorly and pos-teriori v, and soon mav be divided into three segments : the fore-, ff/id-, and of the Mouth.—The cephalic segment, the fore-gut, is somewhatdilated at its anterior extremity, and there constitutes the/)r/w///er/>//rtn«.r, which atfirst is separated from a bay-like depression, the oral recess (stomodauiu ), whichme
Size: 2697px × 926px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthormc, bookcentury1900, bookdecade1910, booksubjectanatomy
