. Cunningham's Text-book of anatomy. Anatomy. THE MESODEBM. 27 Plasmodia! trophoblast Cellular trophoblast Mesoderm lining Wk. trophoblast. Chorion At the cephalic end of the embryonic area the medial margins of the mesodermal sheets fuse together across the median plane, forming a transverse bar of mesodermal cells which may be called the pericardial mesoderm (Fig. 48), because the pericardial sac, which envelops the heart, is afterwards developed from it. The area in which this mesoderm lies may be named the pericardial region of the embryonic area (Fig. 48). Between the bar of pericardial m
. Cunningham's Text-book of anatomy. Anatomy. THE MESODEBM. 27 Plasmodia! trophoblast Cellular trophoblast Mesoderm lining Wk. trophoblast. Chorion At the cephalic end of the embryonic area the medial margins of the mesodermal sheets fuse together across the median plane, forming a transverse bar of mesodermal cells which may be called the pericardial mesoderm (Fig. 48), because the pericardial sac, which envelops the heart, is afterwards developed from it. The area in which this mesoderm lies may be named the pericardial region of the embryonic area (Fig. 48). Between the bar of pericardial mesoderm, the cephalic end of the neural groove, and the medial margins of the mesodermal plates lies a small segment of the embryonic area from which the primary mesoderm entirely disappears, leaving the ectoderm and entoderm in contact. This is the bucco-pharyngeal area. It afterwards becomes the bucco-pharyngeal membrane (Figs. 50, 55), which separates the primitive mouth or stomatodeeum from the cephalic end of the primitive entodermal alimentary canal. As already stated, the bucco-pharyngeal membrane disappears during the third week, when the stomatodseum and the primitive alimentary canal become continuous with each other. Between the bucco- pharyngeal area and the cephalic end of the primi- tive streak the medial margins of the mesodermal plates are separated from one another by the noto-. chord and the neural groove (Fig. 36), and still more caudally they are united with the sides of the streak (Fig. 34). After the permanent mesodermal plates are de- finitely established a series of clefts appear in their peripheral margins. The clefts on each side soon fuse together to form the bilateral rudiments of the embryonic coelom (Fig. 36). The septum of cells at the lateral border of the embryonic area on each side, which, for a time, separates the embryonic from the extra-embryonic ccelom, soon disappears, and the ccelom then forms a continuous cavity (Fig. 37). The embryonic
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
