50 MB. T. J. PAEKBR ON THE INTESTINAL 



6 2. The most couveuient method of preparing the intestine for examination is to 

 distend it, after washing out the contents with a stream of water, with a 0-5-per-cent. 

 solution of chromic acid, and then to place it in a vessel of the same fluid for a few days. 

 By this method the walls become thoroughly hardened, so that windows can be cut in 

 them to any extent without danger of collapse, and the whole extent of the valve 

 examined in a perfectly natural position. At first I adopted the plan of distending the 

 washed intestine with air, and then drying it ; but experience proved that this method 

 was almost worse than useless. 



§ 3. The oesophagus of Eaia enters the abdominal cavity in its antero-dorsal region, 

 and almost immediately passes, with slight increase of diameter, into the stomach. 

 This passes backwards, and slightly to the left, towards the posterior end of its cavity, 

 and then, turning sharply round to the right, and undergoing a marked decrease of 

 diameter, passes forwards to within a short distance of the anterior end of the abdomen, 

 where it becomes constricted to form the pylorus. Beyond this point the alimentary 

 canal immediately widens, forming the intestine; and this, becoming at once bent 

 round to the right, passes at first directly backwards along the right wall of the 

 abdominal cavity, and finally inwards, forming the rectum, until it reaches the middle 

 line and dilates into the cloaca. Thus the intestine, or at any rate that part of it in 

 which the spiral valve is contained (the valve-gut, Klappendarm), is practically a 

 straight tube, and may be described as having an anterior and a posterior extremity, 

 and dorsal, ventral, right, and left sides. 



Tlie superior mesenteric artery passing to the right and somewhat ventralwards from 

 the dorsal aorta, reaches the left side of the intestine a short distance posterior to the 

 pylorus, and immediately passes straight backwards along the left or inner side to the 

 rectum, the superior mesenteric vein running parallel with it. Both artery and vein 

 send off, on each side, a set of branches nearly at right angles, in such a way that of 

 each pair of branches one runs almost transversely along the dorsal side of the gut, the 

 other in the same direction along its ventral side. The dorsal branch is, in every case, 

 given off at a slightly more anterior line than the corresponding ventral branch ; and 

 the two branches, passing to the right, form an incomplete slightly oblique hoop round 

 the intestine. The hoops thus formed, usually ten or eleven in number, correspond 

 with the attachments to the parietes of the intestine of the successive turns of the 

 spiral valves, with the single strange exception of the second, counting from the 

 anterior end ; this is seen, on opening the gut, to correspond to the middle of the 

 space between the first and second turns of the valve. 



The portion of intestine anterior to the first branch of the mesenteric artery and vein 

 is usually distinguished as the duodenal portion, or bursa entiana ; it receives the bile 

 and pancreatic ducts, and is supplied by a special (duodenal) branch of the cceliac 

 artery ; it differs, however, in no other respect from the remainder of the valve-gut. 



The portion of intestine posterior to the last branch of the superior mesenteric 



