233 



THE TISSUES. 



Fi<r. 140. 



I. SCALY EPITHELIUM. 



A. The simple scaly or squamous epithelium consists of a single 

 layer of flattened cells, of a polygonal outline. Fig. 140 shows the 



epithelium of a serous membrane. 



Distribution. This kind of epithe- 

 lium is found covering all true serous 

 (but not synovial) surfaces. It also 

 lines all lymphatics and bloodvessels 

 throughout, and all mucous follicles, 

 the air-cells of the lungs, and the ulti- 

 mate follicles of all true glands. It 

 also covers the membrane of Demours, 

 the posterior surface of the iris (uvea), 

 the inner surface of the choroid coat 

 (the pigment-cells described on page 

 133, there forming a scaly epithelium), 

 and the capsule of the crystalline lens ; 

 and lines the internal ear and the Graa- 

 fian vesicle. 



The simple scaly epithelium lining the seminiferous tubes merges 

 into the simple conoidal at the head of the epididymis, and thence 



the latter variety lines the 

 vas deferens. 



Peculiarities. In some 

 of the large arteries and 

 some of the veins, the epi- 

 thelial cells are quite ir- 

 regularly elongated, fusi- 

 form, and slender, being 



irss to <>b of an incn 

 long. Being also not per- 

 fectly matched to each 

 other, narrow spaces are 

 here and there left be- 

 tween them. (Fig. 141.) 

 Distinct and well-marked 

 epithelium may be traced 

 in vessels only j^-g to jg 1 ^ of an inch in diameter. In the walls 

 of the capillaries, however, only scattered nuclei can be seen; which, 



Scaly epithelium of serous membrane. 

 a. A fold showing thickness of the cells 

 at its dark edges. 6. One of the nuclei. 

 c. Line of junction of two cells. (Mag- 

 nified 300 diameters.) 



Fig. 141. 





Epithelial cells of aorta (horse). The largest, with dark 

 nuclei, are magnified 400 diameters ; the others 200 diame- 

 ters. The 10 smaller at the right are mere nuclei. 



