6 4 



(J) An inner coat, the tunica intima, which consists 

 of a single layer of endothelial cells lining the lumen of 

 the vessel, a thin stratum of sub-endothelial connective 

 tissue, and a stratum of elastic tissue, the elastic intima or 

 ftnestrated membrane of Henle. 



(2) The middle coat, tunica media, composed largely 

 of circularly disposed bundles of non-striped muscle tissue ; 

 between these thin films of elastic tissue, seen in cross 

 section as wavy lines, are found. 



(3) The outer coat, tunica adventitia, consists of 

 bundles of white fibrous tissue felted into a dense network. 

 Between these bundles a few elastic fibres are seen. This 

 coat is continuous with the surrounding connective tissue. 



The wall of the vein is not so thick. Three coats are 

 seen, resembling in structure the ones seen in the artery. 

 In the intima of the vein the elastic tissue is not so prom- 

 inent ; in the tunica media there is relatively less muscle ; 

 the bundles of muscle are separated by white fibrous tissue. 

 The adventitia is thicker .than the corresponding coat of 

 the artery. This section also shows in section a number 

 of small arteries and veins in the fibrous tissue surround- 

 ing the larger vessels. 



Sketch a segment of the arterial wall, also of the 

 venous wall/ and sketch a small artery, all under low power. 



(d) Aorta. 



Small pieces of the aorta were hardened in alcohol, stained in 

 borax carmine, embedded in paraffin, and cross-sectioned. Fix and 

 mount in balsam. 



The media is relatively thick, and is composed of 

 alternating layers of non-striped muscle and yellow elastic 

 tissue. The majority of the non-striped muscle cells are 

 arranged transversely, some few longitudinally. The adven- 

 titia is a relatively thin coat, composed largely of white 

 fibrous tissue, together with a few elastic and non-striped 

 muscle fibres. The intima is composed of endothelial cells, 

 elastic, and white fibrous tissue. Sketch a portion of the 

 wall under high power. 



