Chap, x.] THE HEART AND BLOOD-VESSELS. 



77 



connective tissue, with an admixture of networks oi 

 elastic fibres. 



(a) The endothelium is a continuous single layer 

 of flattened eloii- e 



gated cell plates. 



(b) The inti^ 

 ma in the aorta 

 arid large arteries 

 is a very com- 

 plex structure, rfJ 

 consisting of an 

 innermost layer I 

 of fibrous con- 

 nective tissue, 

 which is the 



u inner longitu- 

 dinal fibrous 

 layer" of Remak, a 

 outside of which 

 is a more or less 

 longitudinally- 

 arranged elastic 

 membrane. This 

 is laminated, and 

 composed of 



fenestrated elastic membranes of Henle. (See page 44.) 

 The larger the artery the thicker the intima. In 

 microscopic arteries the intima is a thin fenestrated 

 membrane, the fibres having distinctly a longitudinal 

 arrangement. 



(c) The media is the chief layer of the wall of 

 the arteries (Fig. 46). It consists of transversely 

 arranged elastic lamellae (fenestrated membranes and 

 networks of elastic fibres), and between them smaller 

 or larger bundles of circularly arranged muscular 

 cells. The larger the artery the more elastic tis- 

 sue is there present in the media, the smaller 



Fig. 45. From a Transverse Section through 

 the Inferior Hesenteric Artery of the Pig. 



e, Endpthelial lining ; i, elastic intima ; m, muscular 

 media ; a, adventitia with numerous elastic fibrils, 

 cut in transverse section. (Atlas.) 



