Chap. III.] 



EPITHELIUM. 





alveoli of secreting and excreting glands, such as the 

 kidney, liver, mammary gland, testis and ovary, the 

 salivary glands, mucous, peptic, and Lieberkiihn's. 

 glands, the sweat and sebaceous glands, the hair 

 follicles, &c., consists of epithelial cells. Such is the 

 case also with the sensory or terminal parts of the 

 organs of the special senses. And, finally, epithelial 

 cells occur in other 

 organs, such as the 

 thyroid gland, the 

 pituitary body, &c. 



The hairs and 

 nails, the cuticle of 

 the skin, certain 

 parts of the rods 

 and cones of the 

 retina, and the rods 

 of corti of the organ 

 of hearing, are modi- 

 fied epithelial struc- 

 tures. 



Epithelial cells 



are grouped together Figi 13A> _ Various kinds of Epithelial Cells. 



by exceedingly thin 

 layers of an albu- 

 minous interstitial 

 cement substance, 

 which during life is 



of a semi-fluid nature, and belongs to the group of 

 bodies known as globulins. 



18. As regards shape we distinguish two kinds 

 of epithelial cells columnar and squamous. The 

 columnar cells are short or long, cylindrical or pris- 

 matic, pyramidal, conical, club-shaped, pear-shaped, 

 or spindle-shaped ; their nucleus is always more or 

 less oval, their protoplasm more or less longitudinally 

 striated. On the free surface of the cells i.e., the 



A, Columnar cells of intestine; B, polyhedral 

 cells of the conjunctiva; C, ciliated conical 

 cells of the trachea; D, ciliated cell oi frog'l 

 mouth; E, inverted conical cell of .trachea; 

 F, siiuamous cell of the cavity of mouth, seen 

 from its broad surface ; o, squamous cell, seen 

 from its narrow side. 



