1112 



Obstruction of the Larger Arteries. 



tissue from the vessel wall takes place which may eventually fill 

 out the vessel, the lumen of which is already narrowed, com- 

 pletely and transform it into a firm connective tissue cord 

 (organization of thrombus). Such a change occurs, however, 

 more often at the places where emboli have become wedged in, 

 which is a fairly frequent occurrence in the smaller peripheral 

 arteries. 



Fig. 197. Thrombosis of the posterior end of the abdominal aorta and of its 



branches, in a horse, a Abdominal aorta; b b' Art. circumflexa ilium prof.; cc' Art. 



iliaca externa ; d d' Art. hypogastrica ; ( e e' Art. obturatoria ; / /' Art. iliolumbalis ; 



g (/ Art. glutaea sup. ; h h' Art. sacralis lateralis. 



Pathogenesis. The obstruction of large arterial trunks pro- 

 duces a peculiar disturbance in the function of the muscles. In 

 the majority of cases the vessel is not completely obstructed by 

 the thrombus, and even if this occurs, a collateral blood circula- 

 tion is established in a short time by the intermediation of 

 branches which pass off proximally to the thrombus. The part 

 of the body which is to be nourished by the obstructed vessel 

 receives also in future a certain amount of blood, sufficient to 



