THE DIGESTIVE SYSTEM 301 



a submucosa, and a layer of smooth muscle. The mucosa is composed 

 of a simple columnar epithelium resting upon a basement membrane 

 and a stroma which contains smooth muscle cells and small mucous 

 glands. The submucosa is a thin layer of connective tissue. Hen- 

 drickson describes the muscular coat as consisting of three layers, an 

 inner circular, a middle longitudinal, and an external obhque. At 

 the entrance of the common bile duct into the intestine, and at the 

 junction of the duct of Wirsung with the common duct, there are 

 thickenings of the circular fibres to form sphincters. In the cystic 

 duct occur folds of the mucosa — the Ileisterian valve — into which 

 the muscularis extends. 



The Gall-Bladder 



The wall of the gall-bladder consists of three coats — mucous, 

 muscular, and serous. 



The mucous membrane is thrown up into small folds or rugcd, 

 which anastomose and give the mucous surface a reticular appearance. 

 The epithelium is of the simple columnar variety with nuclei situated 

 at the basal ends of the cells. A few mucous glands are usually found 

 in the stroma. 



The muscular coat consists of bundles of smooth muscle cells 

 which are disposed in a very irregular manner, and are separated by 

 considerable fibrous tissue. A richly vascular layer just beneath the 

 stroma is almost free from muscle and corresponds to a submucosa. 

 It frequently contains small lymph nodules. 



The serous coat is a reflection of the peritoneum. 



TECHNIC 



(i) Before taking up the study of the human liver, the liver from one of the 

 lower animals in which each lobule is completely surrounded by connective tissue 

 should be studied. Fix small pieces of pig's liver in formalin-Miiller's fluid 

 (technic 6, p. 7). Cut sections near and parallel to the surface. Stain with haem- 

 atoxyUn-picro-acid-fuchsin (technic 3, p. 21) and mount in balsam. In the pig's 

 liver the lobules are completely outlined by connective tissue and the yellow 

 picric-acid-stained lobules are in sharp contrast with the red fuchsin-stained 

 connective tissue. 



(2) For the study of the human liver treat small pieces of perfectly fresh 

 tissue in the same manner as the preceding, but stain with haematoxylin-eosin 

 (technic i, p. 20). 



(3) The secretory tubules and smaller bile ducts may be demonstrated by 

 technic, 5, p. 29. A light eosin stain brings out the liver cells. 



(4) For the study of the blood-vessels of the liver, inject the vessels through 



