372 



THE LARGE INTESTINE. 



canal, consists of external longitncliiial and internal circular fibres. The 

 loufjitudinal fibres, although found in a certain amount all round the 

 intestine, are, in the ca3eum and colon, principally collected into three 

 remarkable flat longitudinal bands (fig. 2G7, / m ; fig. 270). These 

 bands, sometimes called the ligaments of the colon, are about half an 

 inch wide, and half a line thick ; they commence upon the extremity of 

 the crecum, at the attachment of the vermiform appendix, and may 

 be traced along the whole length of the colon as far as the commence- 

 ment of the rectum, where they spread out, so as to surround that part of 



Fis. 267 



Fig. 267. — Outline Sketch op a Sec- 

 tion OF THE AscEKW.xG CoLON (Allen 

 Thomson). 3 



s, the sei'ous or peritoneal covering \ 

 s', s', reflection of this at the attached 

 border forming a short wide mesentery, 

 between the folds of which the blood- 

 vessels are seen passing to the colon ; a, 

 one of the appendices epiploicce hanging 

 from the inner Ijorder ; I m, indicates at. 

 the free border one of the three bands 

 formed by the thickening of the longi- 

 tudinal muscular coat ; the dotted line 

 continued from the margins of these 

 bands represents the remainder of tlio 

 longitudinal muscular coat, and the thick 

 line within it, marked c m, represents 

 the circular muscular layer ; in, the mu- 

 cous membrane at the flattened jiart ; 

 r, the crescentic l)ands or indentations- 

 which divide the sacculi. 



the intestinal tube with a uniform 

 layer of longitudinal muscular 

 "^ fibres. One ofthese bands, named 



the posterior, is placed along the 

 attached border of the intestine ; another runs along its anterior border, 

 and, in the tiansverse colon, corresponds with the attachment of the 

 great omentum ; whilst the third band {lateral) is found on the inner 

 border of the ascending and descending colon, and on the under border 

 of the transverse colon. It is along the course of this third band that 

 the appendices epiploica? are most of them attached (fig. 267, a). Mea- 

 sured from end to end, these three bands are shorter than the inter- 

 vening ]mrts of the tube ; and the latter are thus throAvn into the 

 sacculi already mentioned : accordingly, when the bands are removed 

 by dissection, the sacculi are entirely effaced, and the colon, elongating 

 considerably, assumes the cylindrical ibrm. The transverse constric- 

 tions seen on the exterior of the intestine, between the sacculi, appear 

 on the inside as sharp ridges separating the cells, and are composed of 

 all the coats. In the vermiform appendix the longitudinal muscular 

 fibres form a uniform layer. 



The circvlar muscular fibres form only a thin layer over the general 

 surface of the csecum and colon, but are accumulated in larger numbers 

 between the sacculi. In the rectum, especially towards its lower part^ 

 the circular fibres form a very thick and powerful muscular layer. 



The submucous or areolar coat resembles in all respects that of 

 the small intestine. 



