I20 BIOLOGY OF THE LABORATORY MOUSE 



nuclei are large and round and may be found two in a cell. Mitoses are not 

 found among them. 



The gastric pits of the pyloric region are deep and the gland tubules 

 are short. The glands are lined by columnar cells in which the nuclei are 

 near the base and the cytoplasm contains fine granulations. These cells 

 resemble the mucous neck cells of the gastric glands and are mucous cells. 

 The transition between the fundic and pyloric glands is gradual. 



The lamina propria of the glandular part of the stomach separates the 

 gland tubules from each other, forms the walls of the foveolae and fills 

 the spaces between the glands and the muscularis mucosae. It consists of 

 connective tissue containing fibroblasts, lymphocytes, some eosinophil 

 leukocytes and plasma cells. The muscularis mucosae in both the glan- 

 dular and non-glandular parts consists mainly of longitudinally arranged, 

 smooth muscle fibers. In the glandular part thin strands of smooth muscle 

 project between the glands. The submucosa is composed of loose connec- 

 tive tissue and contains blood and lymph vessels. The muscularis externa 

 is thin in the non-glandular and better developed in the glandular part. It 

 consists of an irregular inner oblique, a well developed middle circular and 

 a thin outer, longitudinal, smooth muscle layer. The circular layer is par- 

 ticularly well developed at the pylorus. About the organ is a serous mem- 

 brane consisting of loose connective tissue containing adipose cells and 

 covered by mesothelium. Frequently a solitary lymph node is present in 

 the serosa at the lesser curvature. 



The small intestine. — The small intestine extends from the pyloric 

 valve to the caecum (about i8 inches). It may be divided into three parts: 

 the duodenum, the jejunum and the ileum. 



The inner surface of the small intestine is covered with villi, delicate 

 finger-like projections of the mucous membrane. Phcae circulares are not 

 present. The villi of the duodenum are tall and leaf-shaped, being wide at 

 the base and narrow at the tip (Fig. 55). In the jejunum and ileum they 

 are cyUndric in shape, tall in the former and short in the latter (Fig. 56). 

 Between the villi are the openings of the simple tubular intestinal glands 

 (crypts of Lieberkiihn). The surface of the villi and the areas between them 

 are covered by simple, very tall, columnar epitheHal cells, having oval 

 nuclei situated in their lower thirds and striated cuticular borders at their 

 free surfaces. These epithelial cells continue into the glands, becoming 

 somewhat shorter near and at the base. The cells near the base of the 

 glands show numerous mitoses. Oval-shaped goblet cells are present, 

 scattered among the columnar cells. The nuclei are pushed to the base, 



