THE DIGESTIVE TRACT. 607 



cle-fibers in a circular and plexif orm arrangement. Both circular 

 and longitudinal layers are uniformly distributed throughout 

 the wall of the rectum, attaining their greatest width near the 

 anus. The transition of smooth to striped muscle-fibers is 

 gradual. 



Blood-vessels of the Intestines. According to C. Toldt, the dis- 

 tribution of the blood-vessels in the intestines closely resembles 

 that of the stomach, their arrangement being nearly identical in 

 the stomach and the large intestine. The arterioles send branches 

 to the peritoneum and pierce the longitudinal muscle-layer, be- 

 tween which a further division takes place by the formation of 

 elongated capillary meshes, for the supply of the two muscle- 

 layers of the intestine proper. After having perforated the 

 circular muscle, always, of course, in the external perimysium 

 which separates the larger muscle-bundles, the arterioles reach 

 the submucous layer, producing, by repeated bifurcations and 

 anastomoses, an extended vascular plexus. Finally, the arteri- 

 oles penetrate the longitudinal muscle-layer of the mucosa and 

 form the terminal arterial plexuses extended beneath the tubular 

 glands, from which arise the terminal arterioles for the supply of 

 the uppermost portions of the mucosa. In the stomach and the 

 large intestine the capillaries are woven around the tubular 

 glands, and widen beneath the surface epithelium to double their 

 original diameters in circular loops around the openings of the 

 tubules. From these superficial capillaries arise the veins, which, 

 at regular intervals, pass downward between the glands and 

 empty into venous plexuses within the mucosa. The efferent 

 veins arising from this plexus accompany the arteries downward. 

 In the small intestine the arterioles penetrate the myxomatous 

 tissue of the villi; each villus contains one or two arterioles, 

 which branch very freely into capillaries. The latter are in con- 

 nection with the capillaries of the tubular 'glands. The veins 

 originate at the apices of the villi from slightly widened capillar- 

 ies. (See Fig. 255.) In the duodenum the acinous glands are 

 supplied with capillaries of their own, and so are all lymph- 

 follicles of the small and large intestine. 



The lymph-vessels of the intestines produce a separate capillary 

 plexus for the muscle-layers and for the mucosa. The former 

 was first described by Auerbach, who found that the lymphatics 

 collect into the so-called interlaminar lymphatic reticulum, lo- 

 cated between the longitudinal and circular muscle-layers. Flat 

 plexif orm extensions of lymphatics exist in the submucous layer 



