480 Mr. C. B. Lockwood. Arteries of the Abdomen 



verse section through an embryo chick at about the third day of incu- 

 bation, displays the alimentary canal suspended from the vertebral 

 region by a long mesentery. The liver commences as a protrusion 

 from the wall of the intestine, and owing to the rapidity of its 

 growth the organ soon attains considerable size. Numerous blood- 

 vessels are present in the mesentery which unites the liver and intes- 

 tine to the spine, and the corpuscles which they contain may be seen 

 to enter into intimate relation with the hypoblastic cells which form 

 the liver substance. This observation is of the greatest importance, 

 for it shows that from its earliest appearance the liver obtains a part 

 of its blood supply from the vessels of the mesentery. Continuing to 

 watch the changes which occur, it will be found that the growth of the 

 liver is very rapid, and that, after a while, it gradually becomes con- 

 stricted at its junction with the alimentary canal. Whilst this con- 

 striction is being formed, the convexity of the growing liver unites 

 with the front wall of the abdomen. The histological changes which 

 accompany these processes are of some importance. The cells which 

 cover the surface of the liver and adjoining parts assume a flattened 

 appearance, and are undistinguishable from those which line the 

 remainder of the pleuro-peritoneal cavity. In other words, the surface 

 of the liver becomes covered with peritoneum. The constriction 

 between the stomach and the liver, at the same time, becomes thinner, 

 and its surface converted into serous membrane. If, at this stage, a 

 recapitulation be permitted, it is evident that the section shows, from 

 the spine forwards, mesentery, intestine, constriction, liver, and 

 attachment of liver to front wall of abdomen. Both Gregenbaur 

 ("Elements of Comparative Anatomy," translated by F. J. Bell, 

 p. 565) and Balfour (" Comparative Embryology," vol. ii, p. 623) 

 point out that this is the usual condition in the vertebrates. The 

 identity of the various parts which have been mentioned has also 

 been recognised by these authors, and seems quite obvious; the 

 mesentery and intestine require no further remark ; the constriction 

 between the liver and the bowel corresponds to the lesser omentum, 

 and the part uniting the liver to the front wall of the abdomen is the 

 same as the falciform ligament. 



A little consideration will show that although the preceding events 

 have been observed in other vertebrates, yet they are applicable to the 

 human subject. Owing to alterations which take place in the mesen- 

 tery this is not so easy in the adult, but at about the fifth month of 

 intrauterine life the whole intestine, including the stomach and 

 duodenum, has a well marked mesentery, and it may be seen near 

 the pylorus that the mesoduodenum, duodenum, lesser omentum, 

 liver, and falciform ligament, form an anatomical sequence. 



These preliminary facts may now be used in an endeavour to eluci- 

 date the course of the hepatic artery. 



