STKUCTUKE OF THE INTESTINES. 



1179 



an outer stratum longitudinale, in which the fibres run longitudinally, and an inner 

 stratum circular e, in which they are circularly disposed. The muscular coat is thicker in 

 the duodenum than in any other part of the small intestine, and it gradually diminishes 

 in thickness until the end of the ileuin is reached. On the other hand, in the large 

 intestine, it is thickest in the rectum and thinner towards the beginning of the colon. 



The stratum longitudinale of the muscular coat is much thinner than the underlying 

 stratum circulare. In the small intestine it forms a complete sheet, continuous all round 

 the gut (Fig. 928), but thickest at its free margin ; whilst in the large intestine it is 

 divided up into three longitudinal bands known as the tcenice coli, which will be more 

 fully described in connexion with the colon. 



The stratum circulare, much thicker than the longitudinal layer, is composed of 

 bundles of muscular fibres arranged circularly round the tube (Fig. 929), and forming in 

 all parts a continuous sheet. Unlike the longitudinal fibres, those of the circular layer 

 take part in the formation of the valves of the pylorus and colon. 



3. Tela Submucosa. The submucous coat is a loose but strong layer of areolar 

 tissue connecting the muscular and mucous coats, on which chiefly depends the strength 

 of the intestinal wall. In addition to forming a bed in which the vessels break up before 

 entering the mucous coat, it contains the glandulce duodenales (Brunneri) (Fig. 929); and, in 

 both small and large intestines, the bases of the solitary lymph nodules lie in it (Fig. 929). 



4. Tunica Mucosa. The mucous membrane constitutes the inner coat of the 

 intestine. It is everywhere composed (Fig. 929) of the following parts : (1) A layer of 

 striated, columnar, epithelial cells, resting on (2) a basement membrane. Outside this 

 lies (3) a layer of retiform tissue, containing a considerable number of scattered lymph 

 cells. This layer is limited towards the tela submucosa by (4) an extremely thin sheet 

 of unstriped muscle, the lamina muscularis mucosae, which is not visible to the naked eye. 

 The mucous membrane is very vascular, particularly in the small intestine. It is thicker 

 in the duodenum than in the jejunum, and thicker in the jejunum than in the ileum. 



Throughout both the small and large intestines the substance of the mucous membrane 

 is closely set with innumerable (small microscopic) tubular glands, known as the gland- 

 ulse intestinales 

 [Lieberkiihni] (O.T. 

 glands or follicles). 

 In shape they are 

 minute straight tubes, 

 like diminutive test- 

 tubes. Their mouths 

 open on the free sur- 

 face of the mucous 

 membrane : their 

 closed ends lie in the 

 deeper part of the 

 mucous coat, and 

 their cavities are lined 

 with columnar epi- 

 thelium. They open 

 on the surface be- 

 tween the bases of 

 the villi of the small 

 intestine, and in the 

 large gut their orifices 

 are found all over the 

 surface of the non- 

 villous mucous mem- 

 brane. 



Submucosa 



Circular, 



muscular fibres 



Longitudinal, ; 



muscular fibres 

 Peritoneum 



Lieberkiihn's 

 gland 



Submucosa - 



Circular_ 

 muscular fibres 



Longitudinal 



muscular fibres"" 

 Peritoneum - 



Villi 



_ Lieberkiihn's 

 gland 

 Muscularis 

 mucosae 

 Brunner's 

 glands 



Circular 

 muscular fibres 



Longitudinal 

 muscular fibres 

 Peritoneum 



Villi 



Blood-vessels 

 forming net- 

 work in sub- 

 mucosa 



. Blood-vessel 



SMM.U INTESTI 



. . FIG. 929. DIAGRAM to show the structure of the large intestiue, the duodenum, 

 Certain Special and the jejunum. 



developments of the 



mucous coat, found in particular regions of the intestinal tube, must next be con- 

 sidered : these are the (1) villi intestinales ; (2) plicae circulares [Kerkringi] (O.T. 

 valvulse conniventes) ; (3) noduli lymphatici solitarii (O.T. solitary glands) ; and (4) 

 noduli lymphatici aggregati [Peyeri] (O.T. Peyer's patches). 



Villi Intestinales. If the mucous membrane of any part of the small .in- 



