296 



HISTOLOGY 



epithelium is greatly stratified (Fig. 262). The dead, outer cells 

 resist abrasion as the cuticle does in the oesophagus of the squid. 



Absorptive tissue. The 

 lumen of the small intestine 

 of a pigeon bears numerous 

 villi. Each of these has a 

 median, connective-tissue 

 frame-work the mucosa. 

 Within the mucosa are nerve 

 fibers, lymphatic vessels, and 

 blood vessels. These vessels 

 are conspicuous, and it is 

 into them that the assimi- 

 lated products are emptied 

 (Fig. 263). The villus is cov- 

 ered with a columnar epithe- 

 lium. There are scattered 

 goblet or mucous cells in this 

 epithelium. These are not 

 concerned with the absorp- 



-.fc.W. 



FIG. 262. Part of a transverse section of the stratified, 

 epithelial lining of a cat's oesophagus, b.m., basement 

 membrane, x 700. 



tion of food. The cells most 

 numerous in this epithelium 



are tall cells with oval nuclei lying in the lower third of each cell. The 



free or distal end of each cell is marked by a dense cuticular border 



which cannot, however, be 



compared with a real cuticle. 

 Lymphocytes are said to 



aid in the absorbing of fats i*^ .,..,. 



as emulsions. Two of these s% 



cells are shown lying be- 

 tween the absorbing cells in 



Figure 263. Others travel 



through the epithelium to lie 



in the lumen of the canal. 



These cells are supposed to 



receive the fatty emulsions 



from the absorbing cells, and 



then find their way back to 



the lymphatic vessels where 



they disintegrate and dis- 

 charge their contents. These 



cells are not confined to the absorbing tissues, but are found in the 



epithelium of the stomach as well. They have a great affinity for 



FIG. 263. Portion of a longitudinal section of a villus 

 from the pigeon's duodenum, showing several absorb- 

 ing cells and two mucous cells, bl.ca., blood capil- 

 lary with blood cells inside; leu., lymphocytes. X 870. 



