526 



THE TISSUES. 



Fig. 353. 



Vessels of the large intestine 

 of a dog, the mucous membrane 

 being cut through perpendicu- 

 larly, a. Artery. &. Capillary 

 network of the surface with 

 glandular apertures, c. Vein. 

 d. Capillary network round the 

 glandular tu,bules in the thick- 

 ness of the mucous membrane. 

 (KClliker.) 



Fig. 354. 



Section of the mucous membrane of the small 

 intestine of the dog, showing Lieberkilhn's folli- 

 cles and the villi. a. Villi. b. Lieberkuhn's folli- 

 cles, c. Other coats of the intestine. 



The lymphatic vessels of the gastric mu- 

 cous membrane form two networks; a fine, 

 superficial, and a deep, coarse one. The 

 nerves, derived from the pneumogastric and 

 the sympathetic, have been seen to enter 

 the muscular layer of the mucous mem- 

 brane, but have not been traced further. 



2. Structure of the Small Intestine. 



The small intestine is divided into the 

 duodenum, the jejunum, and the ileum. 

 Throughout, the mucous membrane has a 

 simple conoidal epithelium ; and its corium 

 has a layer of smooth muscular fibres both 

 longitudinal and transverse (described by 

 Briicke), like that of the gastric mucous 

 membrane; and, at most, ^ of an inch 

 thick. Where certain glands exist, there is 

 but little submucous tissue, the corium be- 

 ing closely connected with the muscular 

 tunic of the intestine. It is more compli- 

 cated in structure, though thinner than the 

 membrane of the stomach; pre- 

 senting, as it does, the villi and 

 several varieties of glands. 



I. The villi (Fig. 354) ex- 

 tend throughout the small intes- 

 tine from the pylorus to the 

 sharp edge of the ileo-caecal 

 valve, being most numerous 

 (50 to 90 upon a square line) in 

 the duodenum and jejunum ; 

 while there are but 40 to 70 on 

 the same surface in the ileum. 

 They are whitish elevations of 

 the corium of the mucous mem- 

 brane, easily seen by the unaid- 

 ed eye, and are set so close to- 

 gether upon and between the 



