CHAPTER VIII. 

 CIRCULATORY SYSTEM. 



Small artery and vein. T.S. from pancreas. (p. 4, 

 s. 22 & 24, c. P., m. B ) (L) The artery is recognised by the 

 greater thickness of its walls. Three tunics are recognisable. 

 The inner (intima), just discernable under this power, shows 

 the wavy internal elastic lamina, on the inner side of which 

 nuclei may be perceived ; outside this is the thicker middle 

 coat (media), consisting of non-striped muscular fibres ; 

 and externally is the outer coat (adventitia) of connective 

 tissue. (//) The inner coat has an inner lining of endothelium, 

 chiefly recognisable by the nuclei of "its cells, beneath this 

 lies the internal elastic membrane (fenestrated membrane of 

 Henle), and between the two hardly recognisable, owing to 

 its thinness is the sub-endothelial connective tissue. The 

 media or muscular coat in an artery of this size consists 

 entirely of muscle. The adventitia generally shows elastic 

 fibres near the muscular coat : not marked in very small 

 arteries. The characteristic feature of the small artery is its 

 purely muscular coat. 



The vein differs from the artery in having thinner walls, 

 the same structures occur in both. The muscular coat, 

 however, frequently contains fine elastic tissue. 



Distended blood vessels. T.S. artery and vein ligatured in a dis- 

 tended condition (p. 3, s. 22 & 24, c. P., m. B.). 



(L) The artery shows a perfectly smooth and unfolded 

 internal elastic lamina, and its walls appear proportionately 

 thinner. The same is observable of the vien. 



