20 



EPITHELIAL TISSUES 



1. Stratified 



(" stratified { 

 squamous"). 



fSuperficial cells, 



II. COMPLEX EPITHELIA those whose cells form several superimposed layers. 



f Forms the epidermis of the skin, and 

 covers the free surface of those 

 mucous membranes which clothe 

 all orifices in direct connection 

 therewith viz., the conjunctiva 

 and cornea ; the external auditory 

 canal ; part of the nasal mucous 

 membrane ; mouth, pharynx, and 

 esophagus; epiglottis and vocal 

 cords ; anus, as high as the internal 

 sphincter ; vagina and external por- 

 tion of the urethra. 



squamous; deeper, 

 polyhedral ; the 

 deepest, columnar 

 in shape. 



2. Transitional.^ 



3. Pseudo-strati- 

 fied columnar. 



Superficial cells only 

 somewhat flat- 

 tened; next deeper 

 layer, pear-shaped ; 

 deepest layers, 

 polyhedral. 



( Superficial cells, co- 



Ilumnar ; || deeper 

 cells, polyhedral 

 { or spindle-shaped, 

 (a) Non-ciliated 



(rare). 

 [ (b) Ciliated. 



Found only in the urinary system 

 viz., pelvis of the kidney, ureter, 

 bladder, and first portion of the 

 urethra. 



(a) Part of vas deferens. 



(b) Respiratory tract; nasal mucous 

 membrane and passages connected 

 therewith, tear-ducts, Eustachian 

 tube, etc., larynx, trachea, and 

 bronchi. 



Genital tract ; epididymis and vas 

 deferens. 



* Usually designated "columnar" by way of abbreviation. Short columnar 

 cells are often called "cubical" or " cuboidal" and are included under this 

 head. 



f In later life these cells lose their cilia. 



\ Cells whose protoplasm has been converted into mucinogen. They maybe 

 considered unicellular, mucus-secreting glands. 



Differentiation of this variety of epithelial tissue, though neglected by some 

 authors, becomes most important in the clinical examination of urine where it 

 is necessary to determine the origin of individual cells. Transitional cells 

 from the bladder are easily distinguished from the stratified cells of the vagina, 

 urethra, or epidermis. 



I The " superficial " cells of this variety extend throughout the entire thick- 

 ness of the membrane. Hence this form of epithelium may in one sense be 

 called " simple " rather than " stratified." 



SPHEROIDAL EPITHELIUM. In their early embryological 

 condition all epithelial cells are nearly spherical in shape, but, 

 apparently from pressure during growth or development, or from 

 other unknown causes, they are distorted according to the direc- 

 tion of the pressure applied, and according to the number of points 

 of application. Pressure unequally applied on many sides natu- 

 rally produces a polyhedral shape. 



