Aids to embryology / by J.S. Baxter.

  • James Sinclair Baxter
Date:
1948
Catalogue details

Licence: In copyright

Credit: Aids to embryology / by J.S. Baxter. Source: Wellcome Collection.

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    more pronounced cases of persistence of the vitello- intestinal duct a fibrous cord may unite the diverti- culum to the umbilicus. Rarely, there may be a fistulous communication between the gut lumen and the exterior. (6) Non-rotation of the intestine sometimes occurs and then the jejunum and ileum lie on the right side, and the large intestine on the left side, of the abdominal cavity. (7) Situs inversus is a condition in which there is mirror-transposition of the viscera. Thus the liver, caecum, and ascending colon are found on the left side, and left-sided organs, the stomach and spleen, are found on the right. This inversion may be con- fined to the abdominal viscera or may affect the thoracic organs as well. The condition is due to the intestinal loops rotating in the opposite direction to the normal. Carey (1920) believes it to be due to the spiral organization of the developing gut becoming reversed in direction. It is interesting to note that the condition is not infrequent among identical twins. The Liver.—The primordium of the liver first appears about the twenty-fifth day as a shallow groove on the ventral aspect of the future duodenal segment of the gut. This groove becomes a tubular evagination which invades the mass of mesoderm, termed the septum transversum, which partially subdivides the coelom into thoracic and abdominal portions (p. 36), and the ventral mesentery which is continuous with it. The hepatic bud enlarges ; part of it remains within the substance of the ventral mesentery and will form the gall bladder and cystic duct; the major part lying in the septum transversum divides into right and left solid buds which branch repeatedly and become organized as anastomosing trabecular cords of cells. Sinusoidal blood spaces derived from the vitelline and umbilical veins lying
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