THE CIRCULATORY SYSTEM. 



453 



these sclerotic areas may be calcified aud project as hard, often brownish, 

 plates with smooth or rough edges. The surface of the aorta may be rough 





FIG. 252. CHRONIC INFLAMMATION OF THE AORTA ATHEROMA OF THE AORTA. 



Section showing involvement of all the layers. The thickening of the intima is irregular and areas of 

 degeneration are seen in its deeper portion. Patches of flbrous tissue are present in the muscularis. A 

 small thrombus is formed upon the surface. 



from erosion over the degenerated areas, and upon these or elsewhere 

 parietal thrombi may form (Fig. 252). Such sclerotic areas are often 

 well marked at the junction of smaller vessels with the aorta. 



We have seen that in the smaller vessels arterio -sclerosis may lead to 

 extreme narrowing or occlusion of the lumen. When this does not occur, 

 and especially in the medium-sized arteries, since the new tissue is less 

 elastic than normal and liable to yield to the pressure of the blood, the 

 lumen may in places be dilated (Fig. 253) or the wall may rupture. In 

 this way aneurisms may form. This is especially apt to occur when 



FIG. 253. CHRONIC ARTERITIS ARTERIO SCLEROSIS. 

 Showing pouching of the wall of the artery at the side on which is the largest formation of new flbrous 



atheromatous degeneration has taken place and the muscularis is either 

 atrophied or degenerated. In the aorta also dilatation and rupture may 

 occur. 



Arterio-sclerosismay be largely limited to the aorta or to other single 

 vessels, or it may occur in special vascular tracts, such as those of the 

 brain or heart. 



