OP THE ARTERIES. 291 



steatomatous productions, &c. are, like the preceding, only the 

 beginning of the calcarious ossification of which the arteries 

 are so often the seat. This ossification is of two kinds, acci- 

 dental and senile. The first has its seat between the inner and 

 middle membranes, and is preceded by one of the above men- 

 tioned alterations. The second, on the contrary, has its seat 

 in the middle membrane, and consists in a transformation of 

 its fibrous rings into osseous ones, more or less extensive. The 

 different parts of the arterial system are not every way equally 

 predisposed to it. The aortic system is oftener affected by it 

 than the pulmonary. The internal projections of the arteries, 

 and the valves of their trunks, are frequently the seat of this 

 affection; the aorta and its principal branches are often in the 

 same case; oftener in the arteries of the inferior members than 

 in those of the superior extremities; pretty often in those of 

 the muscles, heart, brain and spleen ; but rarely in those of the 

 stomach and liver. Finally, Harvey, Riolan, and Loder, have 

 observed the whole arterial system ossified. The ossification 

 of the arteries most generally occurs in old age; accidental os- 

 sification, however, is also sometimes observed in young sub- 

 jects, and in early infancy. This affection of the arteries is 

 not so frequent in woman as in man. It is much more com- 

 mon in cold than in warm climates. 



The effect of arterial ossification, and especially of that which 

 is accidental, is to produce the wearing of the membranes be- 

 tween which it is placed. The ossification of the arteries has 

 been ascribed to a great many causes. The accidental one is 

 a true production or deposition; that which is senile seems to 

 be the. last conditions of the successive changes that the middle 

 membrane experiences during life, but in the first period of 

 which is soft and red. 



433. Excrescences of a fleshy consistence are sometimes 

 found attached to the internal surface of arteries, and espe- 

 cially to the semi-lunar valves which are at their entrance. 



434. The dilatation of the arteries is a very common affec- 

 tion; it may consist: 1st, in a simple loss of elasticity without 

 any apparent alteration of the parietes; 2d, in an alteration of 

 the dilated parietes. 



