ABDOMINAL CAVITY 485 



its mucous surface downwards, upon the bottom of a cork-lined tray, 

 which has been previously rilled with clean water. The jejunum is 

 chosen because its wall is thicker than the ileum, and consequently 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 with the subjacent flocculent submucous 

 coat, with the scissors, in one layer. The circular muscular fasciculi will 

 come into view. 



Coats of the Small Intestine. The small intestine has five 

 coats or strata entering into the formation of its walls, viz. : 



1. Serous. 



2. Subserous. 



3. Muscular. 



4. Submucous. 



5. Mucous. 



The serous coating 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 

 be 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. It 

 need not be taken into account in this dissection. The 

 muscular coat is composed of involuntary, non- striated 

 muscular fibres. These are disposed in two layers, viz., an 

 external stratum of longitudinal fibres, and an internal stratum 

 of circular fibres. Of these the circular layer is the thicker 

 and more distinct of the two. The external longitudinal 

 fibres are spread out, in the form of a thin continuous layer, all 

 round the circumference of the intestine. In that part of the 

 wall opposite the mesenteric attachment the fibres are more 

 thickly disposed than elsewhere. The submucous coat is com- 

 posed of loose areolar tissue which binds the muscular to the 

 mucous co'at. It is more firmly connected with the latter. 

 The mucous coat must be examined throughout the whole 

 length of the jejunum and ileum. 



Dissection. The student has noticed that externally no distinction can 

 be drawn between the jejunum and ileum, with these exceptions, viz., 

 that as the intestine descends it diminishes slightly in its calibre and in the 

 thickness of its walls. It is necessary, therefore, that he should open it up 

 along its whole length, with the view of determining what differences exist 

 internally. Before doing this, about twelve inches of the upper part of the 

 jejunum should be removed and inflated with air. It should then be hung 

 up to dry in order that the folds of mucous membrane, called plicae 

 circulares, may be studied in their continuity. The best way to open the 



