Talk:Book – Manual of Human Embryology 17
Two longitudinal grooves (boundary grooves) on the lateral walls of the anterior part of the digestive tract mark out at an early period a ventral respiratory from a dorsal digestive zone (Kolliker, Flint; compare Fig. 333 and the transverse section of the region in Fig. 317, where the left groove is already indicated). it is true, probably a secondary condition, for in other lung-breathing animals, and among these in the lowest Tetrapoda, the amphibia, the anlage is paired (Remak, G-oette). Nevertheless even in these forms it is not to be homologized with a final (sixth or seventh) pharyngeal pouch, but is to be derived from a swim -bladder ; probably this structure was originally generally paired, and has, as a rule, become permanent only unilaterally (Greil, 1905). PHARYNX AND ORGANS OF RESPIRATION.
326 through the sinus and ductus cervicalis. Ao.-B., aortic arch; Ao. d.
The ciliated cells arise simultaneously in various parts of the oesophagus at a time when the epithelium is two-layered. They appear to belong with the superficial layer, but Schaffer (1904) has found that some of them may be traced through the entire epithelium to the basement membrane.
In some people, this causes blood pressure to drop everywhere else.
DEVELOPMENT OF THE STOMACH. 379 Passing from the oesophagus into the stomach, the cardiac glands become more elongated and more compactly arranged.
- The relation between the dark cells below and the clear cells above is similar to that seen in the stomach and small intestine.
- At 240 mm. both solitary and aggregate nodules of lymphoid tissue have appeared in the tunica propria.
- The original dorsal border forms the greater curvature, and the ventral border becomes the lesser curvature.
- – Griinwald (1910) derives the tonsil from the ventral portion of the second pouch and regards it as equivalent to a thymus metamere.
- They appear to be distended with mucus, derived from the small group of glands emptying into their basal portions.
Such elevations as are seen in Fig. 279, C, have been described both as folds and as villi. Fig.
This prolongation is named the caudal (or postanal) intestine. Keibel and Elze believe that the primitive streak extends beyond the cloacal membrane along the body-stalk, for in several sections the ectoderm covering the body-stalk shows a local thickening which is nearly in contact with the allantoic duct.
Co., coagulum in the yolk-sac; Coag., coagulum in the chorionic cavity; End., endothelium lining a blood-vessel containing five blood-corpuscles, one of which shows a vesicular nucleus; Ent., entoderm, and Mes., mesoderm of the yolk-sac. Von Spee’s Embryo “v.H.” – In 1896 von Spee published a notable contribution to human embryology, to which reference has already been made. In it he describes an embryo, designated “v. H.,” which has heretofore been placed next to Peters ‘s specimen, but which seems older than Herzog ‘s for the following reasons. The axis of the embryo is said to be represented by a primitive groove (not well defined, however) which is absent in Herzog ‘s embryo; the mesoderm extends between the ectoderm and the yolk-sac, reaching the median line; the entoderm of the yolk-sac is not flat, but is cuboidal throughout; the mesoderm of the ventral portion of the yolk-sac is thrown into elevations by the blood islands within it. The age of “v. H.,” obtained through abortion following influenza five weeks after the end of the last catamenia, has been estimated as 17 to 18 days.
He described them as having round and lightly staining nuclei, with relatively abundant protoplasm which stains deeply with eosin. At this stage the islands are not penetrated by blood-vessels.
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