Talk:Book – Manual of Human Embryology 17
243. Loop 2 is between 1 and 3, forming together with 3 an S-shaped curve.
As seen in three models of the stomach, from embryos of 16, 19, and 19.3 mm. respectively, this pyloric portion extends toward the right and slightly apward, to the pylorus. In every case the position of the pylorus is indicated by a local dilatation of the epithelial tube, such as is shown in Thyng’s model from a 13.6 mm. specimen (Fig. 285, A, p. 392). The junction between the corpus and the pars pylorica, measured along the lesser curvature, occurs midway between the pylorus and the cardia. At the place of junction there is an angular bend in the lesser curvature (incisura angularis) and an abrupt change in the diameter of the tube. Form and Position of the Stomach.
The opinion of Kohlbrugge, cited by Kallius, that the ventriculus laryngis is a branchial pouch and therefore the caudal boundary of the arch mentioned, is untenable in view of the late appearance of the ventricle. At all events the material of the sixth arch, which is undoubtedly present (on account of its aortic arch), must pass continuously into that of the arytenoid swelling, since a separating sixth pharyngeal pouch is to be seen (see above, p. 446, 452). Fig.
At 187 mm. the muscularis mucosae, is distinct in the rectum, but is apparently absent from the transverse colon.
D. ph.-br. Ill, ductus pharyngobranchialis of the third pharyngeal pouch; D.
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.
The adenoid tissue is of mesodermal origin. Fig. 322.
Here the fore-gut presents a dorso-ventral cleftlike lumen, both in the oesophageal and gastric regions. The thick ccelomic epithelium is in direct relation with the ventral part of the sides of the fore-gut, as far anteriorly as the lung-bud.
– Pharynx of the embryo Hah in the collection of the First Anatomical Institute, Vienna (about 15 pairs of primitive segments, length about 3 mm.). Ect., ectoderm; Ka., doubtful branchial anlage; Rh., pharyngeal membrane, broken through in two spots.
According to the early observers, the lymphoid tissue arises from the epithelium, aud Retterer (1895 and 1897) has more recently defended this interpretation. It was rightly rejected by Stohr (1889), who concluded that “the lymph-nodules of the intestine arise in the tunica propria, or in the adjacent parts of the submucosa, through mitotic division of the round cells (leucocytes) which are found there.” Similarly Czermack (1893) has maintained that the lymphoid tissue develops as a “condensation of the mesenchyma.” Czermack is probably correct in concluding that the lymphocytes arise in genetic connection with the reticular tissue. The presence of aggregate nodules (Peyer’s patches) in the human intestine at six months and later has been recorded by Kolliker (1861).
The ridge-like portion is the laryngotracheal groove and the rounded end the unpaired anlage of the lungs. These structures make their appearance very early, simultaneously with the last pharyngeal pouches and before the formation of the last two closing membranes, and show at first no connection whatever with the pharyngeal pouch region, except that the anterior end of the laryngotracheal groove extends just to the aboral part of the mesobranchial area. During the further development of the anlage the lungs grow much more rapidly than the remaining parts and form an unpaired, almost spherical vesicle (Figs. 332 and 333), which is in connection with the digestive tract dorsally and passes over into the tracheal groove orally.
Lymphocytes are first recognizable in embiyos of 140 mm. and secondary nodules in one of 235 mm. By this time the tonsil has acquired its characteristic features. – The plicaB triangularis and intratonsillaris are rudimentary structures in man, but may play a part in the manifold modifications of the tonsils which occur in the mammalian series.
– The digestive tract of an embryo of 4.9 mm., shown in median sagittal section. X24 diam.