ABDOMINAL CAVITY 325 



vertebra. Upon each side the aortic plexus is reinforced 

 by several small twigs from the gangliated trunk of the sym- 

 pathetic. The inferior mesenteric plexus, accompanying the 

 artery of that name, and the internal spermatic (or ovarian] 

 plexus of nerves, which accompanies the internal spermatic 

 (or ovarian} artery, are offsets from the aortic plexus. 



Dissection. Removal of the Jejunum and Ileum. Apply 

 two ligatures round the jejunum about an inch below the 

 duodeno-jejunal flexure, and divide the gut between them ; 

 next, place two ligatures round the ileum, about six inches from 

 its union with the large intestine, and divide it in like manner ; 

 then cut through the blood-vessels and the remains of the 

 mesentery close to the wall of the gut, and remove the separated 

 portion. Take the detached portion of the gut to the sink, cut 

 away the ligatures, and clean the cavity of the gut by allowing 

 water from the tap to run through it. 



The coats of the small intestine must be dissected under 

 water. Take a few inches from the upper end of the jejunum, 

 and, having opened it up with the scissors along the line of 

 mesenteric attachment, pin it out, with its mucous surface 

 downwards, upon the bottom of a cork-lined tray which has 

 been previously filled with clean water. The jejunum is chosen 

 because its wall is thicker than that of the ileum, and conse- 

 quently is more easily dissected. Carefully remove the thin 

 serous coat, in order that the subjacent layer of longitudinal 

 muscular fibres may be studied. Then turn the specimen round 

 and pin it down with its mucous surface uppermost. Now 

 remove the mucous membrane and the subjacent flocculent 

 submucous coat, with the scissors, in one layer. The circular 

 muscular fasciculi will then come into view. 



Structure of the Small Intestine. The wall of the small 

 intestine is composed of five coats or strata, viz. : 



1. Serous. 



2. Subserous. 



4. Submucous. 



5. Mucous. 



3. Muscular. 



The serous coat of the jejunum and ileum is complete, 

 except along the line of the mesenteric attachment. It is 

 exceedingly thin much thinner than the layers of the 

 mesentery with which it is continuous. Unless great care 

 is taken in stripping it off, some of the subjacent muscular 

 fibres will be taken away with it. The subserous coat is a 

 scarcely appreciable amount of areolar tissue which inter- 

 venes between the peritoneum and the muscular coat and 

 connects them together. The muscular coat is composed of 

 involuntary, non-striated muscular fibres, which are disposed 

 in two layers, viz., an external stratum of longitudinal fibres, 



1121 h 



