DISSECTION OF THE DOG 27 



Lymphoglandul^. — A few small lymph-glands are lodged between the 

 two layers of the mesocolon. 



Dissection. — Apply a couple of ligatures a little distance apart around the 

 colon where it is entering the pelvis, and the same at the junction of 

 the duodenum and jejunum. Cut between the ligatures and take away 

 all the intestines, except the duodenum and the terminal part of the 

 colon. Remove them to a sink and slit up the entire length of the tube 

 with scissors, cutting along the line of attachment of the mesentery. 

 Wash away the contents, and examine the interior. 



Interior op the Intestines. — The interior of the intestines is lined by 

 a soft, slimy, mucous membrane, generally more or less folded longitudinally. 

 The folds, however, are not permanent, but may be obliterated by distension. 

 In the small intestine, and more particularly in the ileum, elongated oval 

 areas of mucous membrane can generally be distinguished as differing from 

 their surroundings. These are the aggregated lymph-nodules of Peyer (noduli 

 lymphatici aggregati [Peyeri]). Sometimes they are difficult to demonstrate, 

 in which case they may be discovered by holding the intestine between the 

 eye and a good light. 



In the caecum and in the commencement of the colon are numerous large 

 solitary nodules (noduli lymphatici solitarii) composed, like the aggregated 

 nodules, of lymphoid tissue. 



The termination of the ileum should be specially examined. The orifice 

 by which the ileum communicates with the commencement of the colon is 

 narrow, and, viewed from the colon side, is surrounded by a low ridge of 

 mucous membrane, the valve of the colon (valvula coli). Immediately 

 adjacent to the iHac aperture is a constriction marking the junction of 

 csecuni and colon. 



Structure of the Intestines. — A j)iece of intestine should be pinned 

 out on a sheet of cork with the mucous membrane downwards. The thin 

 serous membrane (tunica serosa) should now be dissected off the underlying 

 muscle. It will be noticed that the serous covering of the intestine is thinner 

 than the membrane forming the mesentery with which it is continuous. Now 

 turn the piece of intestine over and examine the mucous membrane (tunica 

 mucosa). If the intestine be sunk in water and the surface thoroughly cleared 

 of mucus, it will present a velvety appearance — most marked in the jejunum — 

 from the presence of delicate projections, the villi. A pocket lens facihta<tes 

 the examination of these. The mucous tunic should now be removed. In 

 doing so, the connective tissue between the membrane and the muscular coat 

 of the intestine — the submucous tissue (tela submucosa) — will be noted as being 

 of somewhat loose texture. An examination of the muscular coat (tunica 

 muscularis) of the tube shows that the fibres are not all disposed in the same 

 direction. The outer, more superficial fibres run longitudinally ; whereas 



