INTESTINAL TKACT OF BIEDS. 177 



undisturbed condition, lies very irregularly folded, or rather crumpled-up dorsad of 

 the duodenum and veutrad of the rectum. Its posterior portion is nearly straight, 

 an extremely common state. The rectum or third portion of the gut extends from c.c., 

 the end of Meckel's tract, to cl., where it enters the cloaca. It is suspended by a long 

 straight piece of mesentery continuous with the mesentery of Meckel's tract. In the 

 figure, as in some of the later cases, the rectum is represented as folded over to the right 

 so that the cut edge of the mesentery from the duodenum to the cloaca is twisted on 

 itself at the point where the caeca are inserted. The large intestine in most birds is 

 extremely short; its condition in Palamedea, where it is convoluted and might be 

 divided into colon and rectum, is unusual. The calibre of the gut varies : the condition 

 seen in Palamedea is very usual ; the duodenum is wider than Meckel's tract, and the 

 rectum is wider than either that or the duodenum. The caeca are equal in size and of 

 moderate length, being intermediate between the short thick stumps of Passerines and 

 the extremely long, irregularly dilated pouches of the fowl. The blood-vessels, shown 

 in black in this and the subsequent figures, are the veins. At p.v. is represented the 

 cut edge of the main portal vein on its way to break up in the liver ; the large factor 

 from the stomach and spleen is not represented, but the three characteristic intestinal 

 factors are figured. These are the anterior mesenteric or duodenal, draining the 

 duodenum, and at x receiving a small factor which runs forwards from the caeca and 

 posterior part of Meckel's tract. The draining of these parts of the intestine by a 

 tributary or tributaries of the duodenal vessel is seen here in a simple form, but, as will 

 be seen later, becomes a peculiar and important structural feature. The second or 

 middle mesenteric factor of the portal drains Meckel's tract; its main axis runs from 

 Meckel's diverticulum, but a strong factor, which I call the " recurrent mesenteric," 

 curves round from backwards following the contour of the tract. The posterior mesenteric, 

 or rectal factor, drains the rectum ; in many birds it arises from two factors which run 

 backwards along the ventral surface of the kidneys and join opposite the junction of 

 the rectum and cloaca, entering the rectal mesentery at that point. These three 

 components of the portal correspond to the three main divisions of the intestines the 

 Duodenum, Meckel's tract, and the Rectum ; they meet nearly at the same point, but, 

 in different birds, the order of their joining to form the common portal differs ; and, 

 after giving considerable attention to the matter, as I cannot find significance in the 

 order of their junction, I shall not refer to it in this memoir. The arteries of the 

 mesentery are small relatively to the veins; their minor branches follow the minor 

 branches of the veins fairly closely ; the main branches arise from the dorsal aorta. 

 The dotted chain marked v.n. in the figure is the part of the " autonomic nervous 

 system " which follows the intestine. It is extremely plain in some birds, as in 

 Palamedea, where it consists of a ganglionated chain following the general contour of 

 the intestinal loops. The nature of my material has not allowed me to follow it out in 

 the majority of my specimens. To certain general points in relation to it I shall recur 

 later. 



