chap, xvii.i THE COLON. 315 



the ascending colon only being unrepresented.* The 

 whole of the large intestine has at one time an exten- 

 sive mesentery, and in some rare cases this condition 

 may persist throughout life. 



Lumbar colotomy. The operation so named 

 consists in opening the colon in the loin behind the 

 peritoneum, for the purpose of establishing an arti- 

 ficial anus. The operation is performed, when possible, 

 upon the left side, in preference to the right, inasmuch 

 as the descending colon is nearer to the anus, is 

 more fixed than is the ascending colon, and has the 

 larger non-peritoneal surface. A meso-colon, moreover, 

 is more commonly met with in the ascending than in 

 the descending part of the large intestine. The position 

 of the descending colon may be represented by a line 

 drawn vertically upwards from a point half-an-incli 

 behind the centre of the iliac crest. In performing 

 left lumbar colotomy an ink line may be drawn 

 vertically upwards from the centre of the crest of 

 the ileum. It will hit the outer end of the last 

 rib. An incision is made across the centre of 

 this line parallel to the last rib, and so planned 

 that the centre of the incision corresponds to the 

 centre of the line. The superficial tissues having been 

 incised, the following structures are then divided 

 in layers in the following order: (1) The latissimus 

 dorsi and external oblique muscles to an equal extent. 

 (2) The internal oblique in the entire length of the 

 incision. (3) The fascia lumborum, with a few of the 

 most posterior fibres of the transversalis muscle. 

 (4) The transversalis fascia. The quadratus lumborum 

 will be exposed in the posterior inch or so of the incision, 

 and usually does not need to be cut. At the seat of 

 the operation the descending colon occupies the angle 



* See a valuable and exhaustive paper on the subject of these 

 malformations in the Brit. Med. Jour. (vol. ii., 1882, p. 574), by 

 Mr. C. B. Lockwood. 



