266 PRINOIPIiES OP YETERINAKY SUEGEET 



—that is, opposite the sigmoid valves ; in other words, at the 

 sinus of the aorta, because this point is exposed to decided 

 blood pressure. Such an aneurism may form adhesions with 

 the neighboring organs, as stomach, liver, etc., or may even 

 produce atrophy of the vertebral columns by its pressure 

 against it. As a rule, they do not produce any symptoms 

 at all during the life of the animal, but may lead to a rapid 

 death by rupturing and internal hemorrhage. In other 

 instances, they have given rise to vertigo, dyspnoea, stagger- 

 ing. Those horses which bleed to death as a result of a rup- 

 tured aneurism, stop suddenly, gasp for breath, fall down 

 and die quickly, the immediate cause of the rupture being an 

 extra muscular effort. 



Describe anev/risms and thrombosis of the posterior aorta. 



The seat of predilection seems to be the quadrification of 

 the aorta. Here an aneurism is either the result of an end-, 

 arteritis, or an embolus obstructs the vessel, coming from a 

 thrombus located in some other vessel. Such an embolus may 

 be swept on further and obstruct the iliac or femoral arteries. 



What anatomical changes are seen in the aorta under these 

 circvmistcmces ? 

 The walls of the aorta are thickened ; the intima espe-. 

 cially has undergone fatty and calcareous changes, also exhib- 

 iting ulcerations. The interior of the artery is more or less 

 obstructed by a thrombus of light color, which may extend 

 anteriorly or posteriorly into the iliac arteries or even femoral 

 artery. 



What symptoms does dilatation and thrombosis of the posterior 

 aorta produce ? 



Rare in the ox, less so in the horse. When standing still 

 or while walking slowly, nothing unusual is noticed. As soon 



