In some mammals, as for instance the rabbit, this furrow persists throughout life as a deep median slit in the upper lip, but in man it becomes almost obliterated and is represented in the adult only by the philtrum. The labial groove, however, does not extend as deeply into the tissue of the frontal lobe in the region of the furrow as it does more laterally, and there is consequently formed in the median line a slight fold lying in the sagittal plane and extending between the lip and the alveolar portion of the jaw, the frenulum labii superioris. Its development is associated with the occurrence of the intermaxillary suture, and a similar frenulum labii inferioris is formed opposite the intermandibular suture. In the 7.5 mm. specimen the large intestine curves forward to join the allantois at the cloaca.
DEVELOPMENT OF THE STOMACH. 375 stomach was found to be neutral, even after the differentiation of the parietal cells. It yielded an abundant precipitate of mucus. Epithelium and Gastric Glands.- In the 10 mm. embryo the free surface of the epithelium is somewhat wavy, whereas the basal surface is nearly smooth.
– The ductus thyreoglossus, or its remains, occurs ventral to the hyoid bone and therefore between the derivatives of the first and second arches (His). The ultimobranchial body makes its appearance, according to Hammar, in embryos of 5 mm. as a cylindrical transformation product of the fifth pouch, or, it might be said, as an appendage of the fourth; the epithelial bodies IV, as well as the thymus anlagen, are defined in embryos of 8 mm. (Tandler, 1909), occasionally perhaps not until somewhat later (see p. 465). The caudal pharyngeal pouch complex separates from the pharynx in embryos of about 14 mm. (frequently only later, according to Hammar, 1904, in embryos over 18.5 mm. in length), and applies itself directly to the thyreoid. A little later, in embryos of somewhat over 15 mm., the lumen of the ultimobranchial body disappears. The small-celled proliferation of the ultimobranchial body, mentioned and figured above, can be perceived in two embryos in the collection of the First Anatomical Institute, Vienna (Nat. 1, with a length of 19.75 mm., and T. 1, with a length of 23 mm.) ; it seems also to have been observed by Tourneux and Verdun (1897) in an embryo of 19 mm.
– The sometimes occurring differentiation of the ventral diverticulum of the fourth pouch into thymus tissue has never been followed directly, but has been assumed on account of the occasional occurrence of thymus lobes on the epithelial body IV. – In the rabbit the second pouch also gives rise to a transitory ventral diverticulum, that is to say, to a thymus anlage (compare p. 456, footnote). walls of the pouch itself (Figs. 324 and 325), and simultaneously there begins on the oral and lateral walls of the dorsal diverticulum and of the pouch itself (Figs. 324 and 325) a proliferation of the epithelium, which very early shows itself, by its histological differentiation, to be the anlage of an epithelial body.
– The pharyngeal membrane as figured by His. X37 diam. A, embryo “Lg,” 2.15 mm.; B, embryo “BB,” 3.2 mm.
The other loops are not so easily defined, but all coils between the caecum and the place of attachment of the yolk-stalk are included in loop 6. to the right side of the body and down toward the pelvis. When this has occurred, the large intestine passes from right to left, ventral to the upper part of the small intestine ; it then descends to the rectum on the left of the small intestine. Fig. 241.
- Branched glands are frequent at birth, and doubtless the branches subsequently become independent glands.
- There is no solid stage in the development of the large intestine.
- Each pulmonary sack ends in a swollen flask-shaped stem bud.
- A, embryo of 4 mm. (Harvard Collection, Series 714); B, embryo of 9.4 mm. (Harvard Collection, Series 529); C, embryo of 23.0 mm. (Harvard Collection, Series 192).
Body of Evidence (CSI Crime Scene Investigation)
313 has been described by Pearce. In a 54 mm. embryo he found them represented by small groups of from ten to fifteen cells, directly connected with the sides of the ducts.
Brand (1877) found no trace of the glands at 3 months, and states that they first appear in the upper part of the small intestine in embryos of 3 1-2 months (110 mm.?). He considered that they are epithelial pits due to the partial fusion of the bases of adjacent villi. Barth (1868) had previously stated that they are produced by the upward growth of the surrounding mesenchyma, but Kolliker (1861) had described them as tubular downgrowths of the epithelium.
Fig. 269. – Models showing the development of the epithelial folds in the middle portion of the oesophagus.
The body-stalk contains the allantois, which is apparently disintegrated near its tip. The terminal sections, however, are well preserved, and the extremity of the allantois is probably recurved. The body-stalk contains also rings of cells, some of them very near the surface. It is not certain that these represent blood-vessels – which would be the first to appear in the embryo – as Herzog interpreted them, and yet it is clear from later stages that the blood-vessels in the body-stalk arise very early. Jung has carefully described similar rings in the body-stalk of his specimen.