MUSCULAR AND MUCOUS COATS OF THE COLON. 855 



inch wide, and half a line tlr%k ; they commence upon the extremity of 

 the caecum, 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 the intestinal tube with a continuous layer of longitudinal muscular 

 fibres. One of these bands, named the posterior, is placed along the 

 attached border of the intestine ; another corresponds with its anterior 

 border, and, in the transverse colon, is situated at the attachment of the 

 great omentum ; whilst the third baud (lateral) is found along the free side 

 of the intestine, that is, on the inner border of the ascending and descend- 

 ing colon, and on the under border of the transverse colon. It is along the 

 course of this third band that the appendices epiploicse are most of them 

 attached. Measured from end to end, these three bauds are shorter than 

 the intervening parts of the tube ; and the latter are thus thrown into the 

 sacculi already mentioned : accordingly, when the bands are removed by 

 dissection, the sacculi are entirely effaced, and the colon, elongating consider- 

 ably, assumes the cylindrical form. The transverse constrictions seen on the 

 exterior of the intestine, between the sacculi, appear on the inside of the 

 intestine as sharp ridges separating the cells, and are composed of all its 

 coats. In the vermiform appendix the longitudinal muscular fibres constitute 

 an uniform layer. 



The circular muscular fibres form only a thin layer over the general sur- 

 face of the caecum 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. 



Fig. 600. 



Fig. GOO. SEMI-DIAGRAMMATIC VIEW OP A SMALL PORTION OF THE Mucous MEMBRANE 

 OF THE COLON. 



A small portion of the mucous membrane cut perpendicularly at the edges is shown in 

 perspective ; on the surface are seen the orifices of the crypts of Liebeikuhn or tubular 

 glands, the most of them lined by their columnar epithelium, a few divested of it and 

 thus appearing larger ; along the sides the tubular glands are seen more or less equally 

 divided by the section ; these are resting on a wider portion of the submucous tissue, 

 from which the blood-vessels are in a part represented as passing into the spaces between 

 the glands. 



The mucous membrane differs from the lining membrane of the small 

 intestine in having no folds, like the valvulse conniventes,' as also in being 

 quite smooth and destitute of villi. Viewed with a lens, its surface is seen 



