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



The colon, sigmoid flexure, and rectum are the only parts of the 

 alimentary canal which await examination. When the primitive 

 intestinal loop was mentioned, a part which extended from the pelvis 

 to the csecal protrusion was left. Keeping in view the fact that the 

 bowel has an abundant mesentery, it remains to be explained how it 

 becomes converted into the ascending, descending, and transverse 

 colons, and how its conversion affects its vascular supply. The 

 simplest way seems to be to trace the movements of the caecum. At 

 its first appearance this cul-de-sac is within the wide umbilical 

 aperture, but as the intestine elongates it performs a tour round 

 the abdomen; from the umbilicus it passes upwards towards the 

 stomach; from thence it journeys into the right hypochondrium, 

 forming the transverse colon, and descending into the right iliac 

 region completes the ascending portion of the gut. When the colon 

 was straight and indistinguishable from the rest of the alimentary 

 tract, its vascular supply consisted simply of vessels which descended 

 along the mesentery; as the bowel travels round the abdomen it 

 carries both mesentery and blood-vessels with it. The peculiarities 

 which are produced in this manner are so slight that they do not 

 seem to demand further notice. 



There is, however, an exception in the case of the middle colic 

 artery, for both the anatomy and the development of the mesocolon, 

 in which it lies, are open to discussion. These questions have already 

 been argued at some length by the author in the paper previously 

 alluded to (p. 477), so that in the present instance they maybe briefly 

 stated. 



As a review of the formation of the omentum and transverse meso- 

 colon naturally leads up to the points at issue, it is convenient to 

 begin by discussing it. 



Both the structures in question were mentioned when the develop- 

 ment of the stomach and colon was being described (p. 477). It may 



D I AGE AM 4. 



S. Stomach fastened to the spine by its mesentery before the latter has become 



great omentum. 



