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



77 



connective tissue, with an admixture of networks of 

 elastic fibres. 



(a) The endothelium is a continuous single layer 

 of flattened eloii- e 



gated cell plates, i 



(b) The inti^ 

 ma in the aorta 

 and large arteries 

 is a very com- 

 plex structure, 3 

 consisting of an 

 innermost layer 

 of fibrous con- 

 nective tissue, 

 which is the 

 "inner longitu- 

 dinal fibrous 

 layer" of Remak, 

 outside of which 

 is a more or less 

 longitudinally- 

 arranged elastic 



Fig 45< _ From a Transverse Section through 

 the Inferior Mesenteric Artery of the Pig. 



membrane. This 

 is laminated, and 



e, Endothelial lining ; l, clastic intima ; TO, mtiprular 

 media; a, advcntitia with numerous elastic fibrils, 

 cut in transverse section. (Atlas.) 



composed of 



fenestrated elastic membranes of Henle (see a former 

 chapter). The greater 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 is the relation of elastic 

 and muscular tissue of the media in favour of the 



