HISTOLOGY 41 



detail the structure of the layers and including a gland and its duct. 

 Label fully, giving the names of the layers, the tissues of which each 

 is composed, and the functions of the tissues. Record the actual 

 magnification. 



Exercise 38.— The Wall of the Intestine. 



(b) The intestine of the mud-puppy, Necturus, is better for this 

 study than the intestine of the frog, but the structures to be observed 

 are found in all vertebrates. On the slide are very thin sections cut 

 across the intestine. Compare with the sections of the stomach that 

 were previously studied (Exercise 7). As in the section of the skin, 

 the nucleus and cytosome of each cell have been stained differently. 

 Identify the gross features of the section with the handlens before 

 studying with the microscope. There are six layers in the wall of the 

 intestine. On the outside is the peritoneum, composed of a single 

 layer of squamous epithelium which is seen from the edge. Beneath 

 this is the longitudinal muscle layer, composed of non-striated muscle 

 cells which are cut across in the section. Under this is the circular 

 muscle layer which is similar to the longitudinal muscle layer, except 

 that the non-striated muscle cells run around the intestine and are, there- 

 fore, cut lengthwise. Do you find any blood vessels in the muscle 

 layers? Internal to the circular muscle layer is the submucosa, which 

 is composed of fibrous connective tissue and contains many blood 

 vessels. What is their function? What is the structure of their walls? 

 Do any of them contain blood cells? The innermost layer, bounding 

 the cavity of the intestine, is the mucosa, or mucous membrane, which 

 is composed of a single layer of columnar epithelium. In this layer 

 are seen many goblet cells, each with a drop of mucus. Can you find 

 places where the mucus is passing into the intestine? Between the 

 mucosa and the submucosa you may be able to see the muscularis 

 mucosae, a very thin layer of non-striated muscle cells. Understand 

 the structure of each of the layers of the wall of the intestine and be 

 able to explain the part each plays in the function of the intestine. 

 Find the mesentery. With which layer of the intestine is it con- 

 tinuous? What kind of tissue forms the middle layer of the mesen- 

 tery? Are there blood vessels in the mesentery? Make a drawing of 

 a narrow strip across the wall of the intestine (1 X measured size pro- 

 jected to table level), showing the cells exactly as they appear under 

 the high-power objective. Label completely, giving the names of the 

 layers, the tissues of wh'ich each is composed, and the function and full 

 classification of each tissue. Record the actual magnification. 



