THE DIGESTIVE SYSTEM 259 



In both fundus and pylorus thicker strands of stroma surround a num- 

 ber of gland tubules, thus separating them into more or less well- 

 defined groups. In addition to the diffuse lymphatic tissue of the 

 stroma, closely packed aggregations of lymphoid cells are found in the 

 shape of distinct nodules, known as ^^ solitary follicles." These occur 

 throughout the entire gastric mucosa, but are most numerous 

 in the pylorus. The nodules are usually egg-shaped, their apices 

 lying just beneath the epithelium, their bases resting upon the muscu- 

 laris mucosae. Less commonly they lie partly in the submucosa. 

 Over the nodules the epithelium is more or less infiltrated with migra- 

 tory leucocytes. Most of the nodules contain germinal centres 

 around which the lymphoid cells are more closely packed than else- 

 where (see page 173). 



The MUSCULARis MUCOSAE (Figs. 156 and 160, m) may consist of 

 a single layer of smooth muscle with cells arranged longitudinally or 

 obliquely, or there may be two distinct layers, an inner circular and 

 an outer longitudinal. From the muscularis mucosae single cells 

 and groups of cells extend into the stroma between the gland tubules. 



2. The submucosa consists of connective tissue, loosely arranged, 

 many elastic fibres, and some fat. It contains the larger blood- 

 vessels and nerves, including the plexus of Meissner (p. 276). 



3. The muscular coat is usually described as consisting of three 

 layers, an inner oblique, a middle circular ,^nd an outer longitudinal. 



In the fundus the muscle bundles run in various directions, so that 

 the division of the muscular coat into layers having definite directions 

 can be made out only in the pylorus. Here the inner and middle 

 layers are thickened to form the sphincter pylori. In the connective 

 tissue which separates the groups of muscle cells are collections 

 of sympathetic nerve cells and fibres, which while much less distinct, 

 are analogous to Auerbach's plexus of the intestine. 



4. The serous coat consists of a layer of loosely arranged connec- 

 tive tissue covered by a single layer of mesothelium. 



TECHNIC 



(i) Remove a human stomach (not more than two or three hours after death) 

 or that of a recently killed dog. Open along the lesser curvature, and carefully 

 remove the excess of mucus by washing with normal saline. Cut pieces through 

 the entire thickness of the wall, one from the fundus and one from the pylorus; 

 pin out, mucous membrane side up, on pieces of cork, fix in formalin- IMiiller's 

 fluid (technic 6, p. 7) or in Zenker's fluid (technic 10, p. 8), and harden in alcohol. 

 Sections are cut as thin as possible, care being taken that the plane is such that 



