EPITHELIUM 



229 



The cells of ciliated epithelium are generally cylindrical or 

 columnar in form, but are sometimes squamous or spheroidal. 



This kind of epithelium lines all the 

 air-passages of the lungs, and the respira- 

 tory tracks of the nostrils; also the 

 cavities of the brain and the central canal 

 of the spinal cord. 



From what has been said it will be 

 seen that the function of epithelium may 

 be the protection of other tissues, the 

 production of motion, or the preparation 

 of a secretion ; or two of these functions 

 may be performed by one and the same 

 epithelial lining. Some epithelial cells have also a sensory 

 function, such as those which line the olfactory region of the 

 nose, and those which form the sensory surface (retina) of the 

 eyeball. 



SUMMARY. 



Fig. 223. Ciliated Epi- 

 thelial Cells from the 

 Mouth of a Frog. Mag- 

 nified 300 diameters. 



/Definition 

 Structure 



EPITHELIUM 



Kinds . 



Functions 



\ 



The cellular tissue which lines the cavities 



and vessels of the body. 

 Consists of cells of various shapes. 

 Simple a single layer of cells. 

 Laminated cells arranged in several 



layers. 

 Squamous flat scale-like cells. Lines 



heart, blood-vessels, lymphatics, and 



serous cavities (Endothelium). 

 Spheroidal globular or polygonal cells. 



Found largely in glands, and hence 



called glandular epithelium. 

 Columnar elongated cells. Lines 



stomach, intestines, and the ducts of 



glands. 

 Ciliated free surfaces clothed with vibra- 



tile cilia. Cilia perpetually in motion. 



Air-passages and cavities of the brain. 

 Protection. 

 Secretion. 

 Sensation. 

 Motion (ciliated). 



QUESTIONS ON LESSON XXXVIII. 



1. What is epithelium ? Where is it to be found ? 



2. What do you know 6f the structure of epithelium ? 



3. Name the different kinds of epithelium, and say what you know of their 



respective characters and positions. 



4. What are the functions of epithelium ? 



5. What are cilia? What is the special use of ciliated epithelium ? 



