862 



THE ALIMENTARY CANAL. 



is at first entirely to the left of the convolutions of the small intestines, but subse- 

 quently the first part of the large intestine, together with the meso-colon, crosses 

 over the upper part of the small intestine, at the junction of the duodenum and 

 jejunum. The caecum and transverse colon are then found just below the liver; 

 finally, the caecum descends to the right iliac fossa, and at the fourth or fifth month 

 the parts are in the same position as in the adult. At first, villous processes or 

 folds of various lengths are formed throughout the whole canal. After a time these 

 disappear in the stomach and large intestine, but remain persistent in the inter- 

 mediate portions of the tube. According to Meckel, the villous processes are formed 

 from larger folds, which become serrated at the edge and divided into separate villi. 



The mode of development of the alimentary canal accounts, in some measure, for 

 the principal complication in the folds of the peritoneum. The stomach being origi- 

 nally straight in form and mesial in position, the small omentum and gastro-phrenic 

 ligament must be regarded as an originally mesial fold with the free edge directed 

 forwards, which afterwards forms the anterior boundary of the foramen of Winslow. 

 Thus the anterior wall of the sac of the omentum, as far as the great curvature of the 

 stomach, may be considered as formed by the right side of a mesial fold, while the 

 peritoneum in front of the stomach belongs to the left side of the same, and a sac of 

 the omentum is a natural consequence of the version and disproportionate growth of 

 the tube between the duodenum and the cardiac orifice of the stomach. It is obvious 

 that the view of the omental sac, according to which its posterior layers are held 

 to return to the duodenum and posterior wall of the body before proceeding to form 

 the transverse meso-colon (p. 829) is more consistent with the phenomena of deve- 

 lopment now described, than that which would make them directly enclose the colon. 

 On the other hand, the further elongation of the omental sac and the whole disposition 

 of the peritoneum, with respect to the colon, must be regarded as having taken place 

 after the assumption by the great intestine of its permanent position. 



Fig. 603*. 



Fig. 603*. SKETCH OF THE HUMAN 

 EMBRYO OP THE EIGHTH OR NINTH 

 WEEK, SHOWING THE COIL OF INTESTINE 

 IN THE UMBILICAL CORD. 



The amnion and villous chorion have 

 been opened and the embryo drawn aside 

 from them ; v, the umbilical vesicle or 

 yolk-sac placed between the amnion and 

 chorion, and connected with the coil of 

 intestine, i' t by a small or almost linear 

 tube ; the figure at the side repre- 

 sents .the first part'of the umbilical cord 

 magnified ; i, coil of intestine ; vi, vitello- 

 intestinal duct, alongside of which are 

 seen omphalo-mesenteric blood-vessels. 



The occurrence of umbilical hernia in 



its various degrees may be referred to the persistence of one or other of the foetal 

 conditions in which a greater or less portion of the intestinal, canal is contained in 

 the umbilical cord ; and it has been shown that the most common diverticulum of 

 the small intestine is connected with the original opening of the ductus vitello-intes- 

 tinalis into the ileum (p. 841). 



THE LIVER 



The liver is an important glandular organ, very constant in the animal 

 series, being found in all vertebrate, and, in a more or Itss developed con- 

 dition, in most invertebrate tribes. It elaborates and secretes the bile, and 

 otherwise acts, in a manner as yet imperfectly understood, as an elaborator 

 and purifier of the blood. In the exercise of this latter function, there is 

 formed in its texture an amyloid substance, very easily converted into sugar. 



The liver is the largest gland in the body, and by far the most bulky of 



