PATHOLOGICAL STATES OF THE VESSELS. 



513 



Fig. 343. 



its course is limited to the mutual apposition of fusiform cells, or 

 of those furnished with three principal processes. 



Pathological Conditions and New formations of the Vessels. 



The larger arteries are liable 1. To atheromatous deposits (p. 312); 

 these occurring in the annular fibrous layer (i. e. next external to 

 the fenestrated). (Figs. 198 and 199.) It appears to be due to im- 

 perfect nutrition by the vasa vasorum ( Wedl), and is therefore one 

 form of atrophy. The arterial wall becomes weaker in proportion 

 to the accumulation of the fat ; and, becoming dilated, an aneurism 

 is very often produced. 2. By the collapse of their walls (as by 

 pressure, ligature, &c.), the arteries become transformed into liga- 

 mentous cords, and finally into mere fibrils of collagenous tissue, 

 covered with a finely granular substance. 



3. The veins undergo essentially the same changes in atrophy, 

 and varix is the consequence. The depo- 

 sit is usually a finely granular pigment- 

 substance. This change also occurs in 



their valves. 



4. The capillaries are liable to a fatty 

 degeneration of their walls; fatty gran- 

 ules and minute oil-drops being deposit- 

 ed in them, especially around the nuclei. 

 (Fig. 3i3.) The minute arteries also un- 

 dergo a similar change, especially' in the 

 brain of apoplectic persons; and which 

 leads to rupture, and the hemorrhage in 

 which the apoplexy consists. 



5. Pathological new formations of vessels 

 occur in two ways: ls, by extension from 

 pre-existing vessels; and, 2dly, by inde- 

 pendent development in exudations un- 

 dergoing organization. In the latter case, Fatty degeneration of minute ar _ 



the processes Of VariOUS Stellate Cells meet, teries and capillaries of the brain, 



the dissepiments are absorbed, and a net- in white softening. Numerous mi- 

 work Of Vessels is produced, Of Unequal * oil*lobnle. are seen aggregated 

 ?. . * along their walls. 



dimensions, since the processes are far 



slenderer than the bodies of the cells. Finally, however, the diame- 

 ter becomes uniform throughout the plexus, and is usually greater 

 than that of the capillaries of normal tissue. Subsequently, also, 

 blood-corpuscles are developed in the plasma contained in the new- 

 formed vessels; but which cannot pass into the general circulation 

 till a communication is established with it by them. 



33 



