Incidence of Some Aetiological Factors in Human Leukaemia

a fine network of arteries situated immediately under the mucous membrane between it and the muscularis mucosae (Special Plate, Fig. 4). From this plexus very fine-arteries pass up into the mucosa vertically from the horizontal mucosal plexus, and in Fig. 5, on the Special Plate, the mucosal plexus can be seen giving off numerous mucosal arteries. The mucosa has a very rich blood-supply, and it is true to say that the mucous membrane rests on a carpet of blood-vessels, as has been well shown by Brockis and Moffat (1958) in their " neoprene " latex injections of these plexuses. An injection of the venous system shows that the veins follow an identical pathway and pattern to the arteries, forming similar plexuses. The veins drain from the capillary plexus which is in the mucosa itself as small mucosal veins to join the submucosal plexus. No muscular branches are given off by either the long or short arteries, the circular muscle and the taeniae coli receiving their blood-supply from the submucosal plexus. A muscular plexus is formed from arteries arising from the submucosal " macromesh " on the mucosal surface of the circular muscle, and from this plexus smaller arteries are given off which pierce the muscle to form the intramuscular plexus. Special Plate, Fig. 6 shows the muscle coats of the colon after dissection of the mucous membrane and the submucosal plexus, from which it can be seen that the muscle has a poor vascular pattern made up of small arteries.