SQUAMOUS, STRATIFIED, AND TRANSITIONAL EPITHELIUM 55 



Where a layer of epithelial cells comes in contact with the 

 underlying connective tissue, the deepest epithelial cells often rest 

 upon a thin basement membrane, which is modified connective 

 tissue, either structureless or made of flattened cells. 



The succeeding pages will show that epithelial cells may e 

 squamous or columnar, ciliated or otherwise, simple or stratified. 

 These varieties of epithelium are distributed as follows, giving cinly 

 their most important locations: 



Simple 

 Squamous 

 Epithelium 



Stratified 

 Squamous 

 Epithelium 



Simple 

 Columnar 

 Epithelium 



Stratified 

 Columnar 

 Epithelium 



The alveoli of the lungs. 



The capsule of the Malpighian body and the descending limb of 

 the loop of Henle in the kidney. 



The covering of the skin, of the eye, mouth and tongue, 

 pharynx, oesophagus, epiglottis, and of the upper part of 

 the larynx. 



The lining of the urinary tract from the pelvis of the kidney 

 down (except part of the male urethra), most of it being 

 of the special variety of stratified squamous epithelium 

 known as transitional. 



The lining of the vagina. 



The alimentary canal from the beginning of the stomach to the 

 lower part of the rectum; the ducts of its glands and of 

 many other glands; the seminal vesicles, ejaculatory ducts, 

 and part of the male urethra; the surface of the ovary. 



It is ciliated in the uterus and Fallopian tube, the central canal 

 of the spinal cord, and the cerebral ventricles. 



It is ciliated in the most important situations: The trachea 

 and bronchial tubes, the Eustachian tube, the upper part of 

 the pharynx, the lower part of the nasal cavity, the vas 

 deferens. 



SQUAMOUS, STRATIFIED, AND TRANSITIONAL EPITHELIUM 



The simplest method of tissue production by means of flat cells 

 is that of superposition, constituting squamous epithelium. Cells 

 are placed one over the other, generally without great regularity. 

 If regular, and in several layers, the structure is called stratified 

 epithelium; if only in a few layers, it is termed transitional epithe- 

 lium. The superficial layer of the skin affords an example of 

 squamous, stratified epithelium. The bladder and pelvis of the 

 kidney are lined with transitional epithelium. 



The thin, flat .scales from the mouth may be demonstrated by 

 scraping a drop of saliva from the tongue with the handle of a 

 scalpel, transferring it to the slide, and applying the cover. The 



