ELEMENTS OF HISTOLOGY. 



[Chap. X. 



the artery the more muscular tissue. In micro- 

 scopic branches of arteries the media consists 



almost entirely of cir- 

 cular non-striped muscle 

 cells with only few elas- 

 tic fibres. 



100. In the last 

 branches of the micro- 

 scopic arteries, the mus- 

 cular media becomes dis- 

 continuous, inasmuch as 

 the (circular) muscular 

 cells are arranged not as 

 a continuous membrane, 

 but as groups of small 

 cells (in a single layer) 

 in a more or less alter- 

 nate fashion. 



When the media 

 contracts, the intima is 

 thrown into longitudinal 

 folds. 



The aorta has, in the 

 innermost and in the 

 outermost parts of the 

 media, numbers of lon- 

 gitudinal and oblique 

 muscle cells. Accord- 

 ing to Bardeleben, all 

 large and middle-sized 

 arteries have an inner longitudinal muscular coat. 



101. Between the media and the next outer layer 

 there is, in larger and middle-sized arteries, a special 

 elastic membrane, the elastica externa of Henle. 

 (d) The adventitia is a relatively thin fibrous con- 

 nective tissue membrane. In large and middle-sized 

 arteries there are numbers of elastic fibres present, 



Fig. 46. Transverse Section through 

 a Microscopic Artery and Vein in 

 the Epiglottis of a Child. 



A, The artery, showinj? the nucleated 

 endothelium, the circular muscular 

 media.andatrtthefllmnis-tissueadven- 

 titia; v, the vein, showing the same 

 layers ; the media is very much thinner 

 than in the artery. (Atlas.) 



