794 A MANUAL OF ANATOMY 



The diameter of the duodenum is from i J to 2 inches. 



Jejunum — Peritoneum. — There is a mesentery, and the bowel is sur- 

 rounded by peritoneum except along its mesenteric border. Muscular Coat. — 

 This is comparatively thin. Mucous Coat. — This has the following characters : 

 (i) valvulse conniventes, (2) villi in abundance, (3) Lieberkiihn's crypts, 

 (4) solitary glands, and (5) Peyer's patches in its lower half. 



The diameter of the jejunum is about i^ inches. 



Ileum — Peritoneum. — In this respect the ileum resembles the jejunum. 

 Muscular Coat. — This is very thin. Mucous Coat. — The characters of 

 this coat are as follows: (i) valvulae conniventes in upper half, but 

 small and sparse, there being none in the lower half; (2) villi, but in fewer 

 numbers; (3) Lieberkiihn's crypts; (4) solitary glands; and (5) Peyer's 

 patches. 



The diameter of the ileum is about j^ inches. 



Large Intestine. — ^The wall of the large intestine, which is sac- 

 culated, is composed of four coats — serous, muscular, submucous, 

 and mucous. 



The serous coat forms a complete investment to the vermiform 

 appendix, caecum, transverse colon, and pelvic colon. As regards 

 the ascending colon, descending colon, and iliac colon, it is incom- 

 plete, being absent behind. 



The muscular coat {muscularis externa) is composed of plain 

 muscular tissue, disposed in two layers — external or longitudinal, 

 and internal or circular. 



The longitudinal muscular fibres are for the most part collected into 

 three flat bands, called taeniae coli, or ligaments of the colon, except 

 upon the rectum. In the intervals between these bands there are 

 some longitudinal fibres, but they are very few and scattered. The 

 taeniae, which are about ^ inch in breadth, commence upon the 

 caecum at the base of the vermiform appendix, and they extend 

 along the several parts of the large intestine as far as the rectum, 

 where they spread out and form a continuous covering, which com- 

 pletely surrounds that part of the bowel . Upon the caecum, ascend- 

 ing colon, descending colon, and iliac colon the taeniae from their 

 disposition are called anterior, postero-internal, and postero- 

 external. Upon the transverse colon they are so placed as to be 

 called anterior or omental (great omentum), postero-inferior, and 

 superior or meso-colic (transverse meso-colon). They are shorter 

 than the bowel to which they are applied, with the result that the 

 tube is drawn together or puckered, and thus thrown into sacculi. 

 There being three taeniae, there are three rows of sacculi between them, 

 and, inasmuch as the taeniae are placed at nearly equal distances 

 from each other, the sacculi are pretty much of equal dimensions. 

 Between the successive sacculi there are cohstrictions, usually 

 containing fat. The sacculi give rise internally to large pouches, 

 and the constrictions between the sacculi produce internally sharp 

 crescentic rugae, which separate the pouches from each other. When 

 the taeniae are divided, the sacculi and constrictions entirely disappear, 

 and the large bowel becomes elongated into a smooth cylindrical 

 tube. Along- the course of the taeniae there are a number of small 

 processes of peritoneum containing fat, called appendices epiploicae. 



