. A laboratory manual and text-book of embryology. Embryology. 188 THE ENTODERMAL CANAL AND ITS DERIVATIVES the dorsal surface of the tail. The alveoli of the gland are developed as darkly staining cellular buds in embryos of 40 to 55 mm. The islands characteristic of the pancreas appear first in the tail at 55 mm. Owing to the shift in the position of the stomach and duodenum during development the pancreas takes up a transverse position, its tail extending to the left. To its ventral sur- face is attached the transverse mesocolon.. Pericardial Cai/ifu Surface of fore-gut Pleuro-pericardia t

- Image ID: RE069X
. A laboratory manual and text-book of embryology. Embryology. 188 THE ENTODERMAL CANAL AND ITS DERIVATIVES the dorsal surface of the tail. The alveoli of the gland are developed as darkly staining cellular buds in embryos of 40 to 55 mm. The islands characteristic of the pancreas appear first in the tail at 55 mm. Owing to the shift in the position of the stomach and duodenum during development the pancreas takes up a transverse position, its tail extending to the left. To its ventral sur- face is attached the transverse mesocolon.. Pericardial Cai/ifu Surface of fore-gut Pleuro-pericardia t
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Image ID: RE069X
. A laboratory manual and text-book of embryology. Embryology. 188 THE ENTODERMAL CANAL AND ITS DERIVATIVES the dorsal surface of the tail. The alveoli of the gland are developed as darkly staining cellular buds in embryos of 40 to 55 mm. The islands characteristic of the pancreas appear first in the tail at 55 mm. Owing to the shift in the position of the stomach and duodenum during development the pancreas takes up a transverse position, its tail extending to the left. To its ventral sur- face is attached the transverse mesocolon.. Pericardial Cai/ifu Surface of fore-gut Pleuro-pericardia t Canal Entoderm of gut Peritonea I Cavity 1 BODY CAVITIES, DIAPHRAGM AND MESENTERIES The Primitive Ccelom and Mesenteries.—In the Peters embryo the primary mesoderm has already split to form the extra-embryonic ccelom (Fig. 232). When the intra-embryonic mesoderm differentiates, numerous clefts appear on either side between the somatic and splanchnic layers of mesoderm. These clefts coalesce in the cardiac region and form two elongated cavi- ties lateral to the paired tubular heart. Simi- larly, right and left pleuro-peritoneal cavities are formed between the mesoderm layers caudal to the heart. The paired pericardial cavities ex- tend toward the midline cranially and com- municate with each other (Fig. 181). They also are prolonged caudally until they open into the pleuro-peritoneal cavities. These in turn communicate laterally with the extra- embryonic ccelom. In an embryo of 1.5 mm. the ccelom thus consists of a U-shaped peri- cardial cavity, the right and left limbs of which are continued caudally into the paired pleuro-peritoneal cavities; these extend out into the extraembryonic ccelom. When the head-fold and fore-gut of the embryo are developed, the layers of splanchnic mesoderm containing the heart tubes are folded together ventral to the fore-gut and form the ventral mesentery between the gut and the ventral body wall (Fig. 182). Owing to the position of the yolk-sac,

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