endothelium, pl. endothelia
en-db-thTclT-\m, en-db-thTc-lT-^
a layer of flat cells lining especially blood and lymphatic vessels and the heart.
epithelium, pl. epithelia
ep-i-thTclT-\m, ep-i-thTclT-^
[TA]; the purely cellular avascular layer covering all the free surfaces, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.
Stedmans Concise Illustrated 4th Ed CD - the books well worth the $25 or so!