THE VEINS 



153 



is considerably thinner than that of the arteries; it contains circular un- 

 striped muscular fibers mingled with a large proportion of yellow elastic and 

 white fibrous connective tissue. In the large veins near the heart the middle 



FIG. 150. Transverse Section through a Small Artery and Vein of the Mucous Membrane 

 of a Child's Epiglottis; the artery is thick- walled and the vein thin- walled. A, Artery; the letter 

 is placed in the lumen of the vessel, e, Endothelial cells with nuclei clearly visible; these cells 

 appear very thick from the contracted state of the vessel. Outside it a double wavy line marks 

 the elastic tunica intima. m. Tunica media consisting of unstriped muscular fibers circularly ar- 

 ranged; their nuclei are well seen, a, Part of the tunica adventitia, showing bundlespf connective- 



than that of the artery. X 350. (Klein and Noble Smith.) 



FIG. 151. A, Vein with valves open. B, vein with valves closed; stream of blood passing 

 off by lateral channel. (Dal ton. ) 



