(After F. P. Johnson.) the epithelial proliferations described in the preceding section. There, as seen in Fig.
Oes., oesophagus; Pr. ver., a dilatation of the lower limb of the intestinal loop, which gives rise to the processus vermiformis and the csecum, and which marks the boundary between the small intestine above and the large intestine below; Vea.
Lewis (1903) found similar detached cysts in the liver of a 12 mm. pig, and considered them to be cut off from the secondary hepatic ducts. Whether they are detached portions of the hepatic ducts is questionable. They may arise in situ by a transformation of the cells of the hepatic trabecular The Periportal Ducts.- In an embryo of 22.8 mm. (Fig. 293, A) the spread of the bile-ducts along the main branches of the portal vein has begun.
E., upper limb; P. mg., plica mesogastrica; Un., mesonephros. X 35. Fig.
– The digestive tract of an embryo of 22.S mm. (Harvard Collection, Series 871). X6 diam. (Drawn by F. P. Johnson.) In addition to the structures lettered as in previous figures the following are shown.
X 90 diam. (After F. P. Johnson.) A, embryo of 37 mm. (Harvard Collection Series 820). B, 42 mm. (Harvard Collection, Series 838). C, 120 mm. there are two sorts of vacuoles, those due to the accumulation of intercellular fluid and those due to an active moving apart of the cells.
The anlage is recognizable before the first pharyngeal pouch has come into contact with the ectoderm, as a prominence in the ventral wall of the pharynx (Figs. 314 and 315) ; it appears, therefore, much earlier than is shown in the Normentafel. It then becomes constricted to form a stalked vesicle (Figs. 317 and 318), and its stalk, whose lumen becomes obliterated, persists for some time as an epithelial cord. The thyreoid anlage belongs primarily to the medial region between the first two ventral pharyngeal grooves, that is to say, to the oral portion of what is later the area mesobranchialis.
The remains of the pharyngeal pouch are still to be seen, according to Hamrnar (1904), in an embryo of 24.4 mm. H. Rabl (1909) finds in the mole a common anlage for the two pouches and names it the caudal pharyngeal diverticulum.
For an account of the differentiation of the anlage see p. 468. Fig. 314. – Pharynx of the embryo Klb (Kromer-Pfannenstiel ; Normentafel, No. 3; 5-6 primitive segments, length, determined from the number of sections, 1.38 mm.).
- cl., membrana cloacalis; Pane.
- – Schema of the branchiogenic derivatives in man,
- The expression telobranchial body, which has been frequently employed recently, has been rejected by H.
– Congenital pyloric stenosis is essentially an excessive development of the circular musculature of the pylorus. The other layers in this region, especially the longitudinal layer, may be more or less hypertrophied, and the folds of the mucous membrane are sometimes so highly developed that they appear to obstruct the lumen. Lymphatic vessels appear in the submucosa in embryos of 214 and 240 mm. Lymph-nodules were found at birth in a considerable percentage of the cases examined by Fischl. They were observed in all parts of the stomach ; sometimes they were at the base of the glands, and did not extend upward between the tubules.
268. – Models showing the epithelial tube of the oesophagus cut longitudinally. X 120 diam .
11 His work affords an independent confirmation of Forssner’s conclusions, and shows that Schridde was in error in denying the presence of vacuoles. Vacuoles in the Epithelium. – In human embryos of about 20 mm., large vacuoles occur in the oesophageal epithelium, so that in cross section the oesophagus may appear to have two or three lumina. This was noted by O. Schultze in 1897.
On the upper side of the vein in Fig. 293, B, the ducts are in the earlier stage of development.
Body of Evidence (CSI Crime Scene Investigation)
Early Development. – In a 10 mm. embryo the large intestine consists of an epithelial tube, an undifferentiated layer of mesenchyma, and, except along the mesenteric attachment and near the pelvic termination, a layer of peritoneal epithelium.
In the stomach, as in both small and large intestine, there are at first irregular coarse depressions (pits and intervillous spaces), from the bottom of which glands extend downward. The cells of the pits and villi are characteristically clear, whereas those at the depths of the glands are granular and deeply staining. The transition between the two is not abrupt, as shown in Fig. 275, B.