EPITHELIUM 



ten. in. 



Bndothelium. Epithelium of similar appearance is found lining 

 the interior of the whole of the vascular system, heart, arteries, capil- 



FIG. 30. Peritoneal surface of a portion of the septum of the great lymph-sac of a frog. The stomata, 

 some of which are open, some collapsed, are well shown, x 1(30. (Klein.) 



laries, veins, and lymphatics, and in the adjuncts of the circulatory 



system called the serous membranes (pericardium, peritoneum, etc.). 



This epithelium is formed from the middle layer of the embryo, 



FIG. 31. A portion of the great omentum of dog, which shows, amongst the flat endothelium of the 

 surface, small and large groups of germinating endothelium, between which are many stomata. 

 X 300. (Klein.) 



the mesoblast ; most other epithelium is derived either from epiblast or 

 hypoblast. Hence it has received a distinct name, viz.: endothelium. 



