. Cunningham's Text-book of anatomy. Anatomy. llantoic diverticulum from entoderm vesicle Cephalic end of embryonic area Pericardial mesoderm'" Mesoderm entoderm vesicle Entoderm Xotochord Fig. 48.âSchema of Sagittal Section of Embryonic Area and Amnion before the Folding of the Area has commenced. Amnion cavity Neural tube - Region of anterior neuropore Ectoderm of amnion The transformation of the relatively fiat embryonic area into the form of the embryo is due, in the first instance, to the rapid extension of the median part of the area, as contrasted with the slower growth of its
. Cunningham's Text-book of anatomy. Anatomy. llantoic diverticulum from entoderm vesicle Cephalic end of embryonic area Pericardial mesoderm'" Mesoderm entoderm vesicle Entoderm Xotochord Fig. 48.âSchema of Sagittal Section of Embryonic Area and Amnion before the Folding of the Area has commenced. Amnion cavity Neural tube - Region of anterior neuropore Ectoderm of amnion The transformation of the relatively fiat embryonic area into the form of the embryo is due, in the first instance, to the rapid extension of the median part of the area, as contrasted with the slower growth of its mar- gins, and the later modelling of the various parts of the embryo is due to different rates of growth in different parts of the embryonic region. By the rapid proliferation of cells from the nodal grow- ing point, at the cephalic end of the primitive streak, the cephalo-caudal length of the area is increased, whilst the cephalic and caudal ends of the area remain relatively fixed, conse- quently the area be- comes folded longitu- dinally. At the same time, the cephalic end of the neural groove is pushed away from the nodal point until it lies at first dorsal and then cephalad to the cephalic border of the area. As a result of this move- ment the bucco-pharyn- o-eal and the pericardial areas become reversed in position, and a cephalic or head fold is formed. This is bounded dorsally by what is now the cephalic portion of the embryo ventrally by the reversed pericardial region, and its cephalic end is formed by the extremity of the head region and the bucco-pharyngeal Amniotic mesoderm Chorionic mesoderm Region ot posterior neuropore Cloacal membrane Body stalk Hind-gut "â - Allantoic Bucco-pharyngeal .' I / V diverticulum membrane | pericardium Mid-gut Fore-gut (heart not shown) Fig. 49. Schema of Sagittal Section of Embryonic Abba shortly after the Folding has commenced. The pericardial mesoderm is carried into the ventral wall of the fore-gut and the coe
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
