OF THE ARTERIES. 287 



The parietes of the arteries augment in thickness and densi- 

 ty during the period of growth; they still continue to increase 

 in density during the remainder of life. 



The variations in the distribution of the arteries arc much 

 more frequent than is generally imagined. Bichat and Meek- 

 el* have justly remarked, that they are at least as often met 

 with, as those of the veins, and perhaps even more frequently. 

 It is especially in the larger arteries that they are remarkable,! 

 both by their frequency, and by a sort of regularity or sym- 

 metry, and by the resemblance they then present with the 

 regular state of certain animals. 



425. Besides the accidental vessels already indicated [371,] 

 when a principal artery is interrupted in its continuity, there 

 are established also other passages for the circulation. These 

 new passages are commonly formed out of the ancient small 

 vessels, but greatly enlarged, which were previously white, 

 by their extreme thinness, become red, or which, being red 

 and capillary, become more voluminous; but which, before 

 this circumstance, formed, by their anastomoses, collateral 

 passages [350]. In certain cases circulation is re-established 

 through passages entirely of a new formation. This fact, 

 the existence of which was suspected by J. Hunter, by Mau- 

 noir and even by Jones, although he controverted Maunoir's 

 opinion, has been put beyond question by the experiments 

 of Dr. Parry.J If the carotid artery of a sheep be tied, or 

 a part be removed, an artery which furnishes no branches in 

 the whole extent of the neck, we find some time after, the cir- 

 culation re-established in the very place where the artery has 

 been obliterated or cut off, by several branches nearly parallel, 

 occupying the interval which exists between the divided ex- 

 tremities of the artery. 



426. The general inflammation of the arteries is of a rare 

 occurrence; their local inflammation is, on the contrary, often 

 met with. Simple redness, however, is not sufficient to charac- 

 terize it; there is, moreover, some thickening or softening in 



* Deutschus archiv. fur die physiologic. 



f Fr. Ticdemann, Tabula artcriarum corp. humani. Calsruhae, 1822. 



* Loc. cit. 



38 



