Etiology, Anatomical Changes, Symptoms. 1107 



undergo may be considered to stand in causal relation to the frequency of aneurysm, 

 and according to Palat the same holds true for 'bus horees. 



In exceptional cases the commencement of the development 

 of an aneurysm corresponds, as to time, with external influences, 

 such as moving a heavy load, jumping, being thrown, or struck 

 on the trunk, etc.,, or it may l)e referred to such an accident with 

 a degree of probability. In such cases the traumatic factor of 

 a sudden excessive rise in blood pressure might cause a par- 

 tial tear in the aortic wall, in consequence of which the weak- 

 ened arterial wall eventually bulges out. On the other hand it 

 is not impossible that even in such cases the wall of the vessel 

 was not quite healthy before the accident. 



Anatomical Changes. A portion of the aorta is either 

 evenly dilated (Aneurysma cylindricum) or the healthy portion 

 gradually passes into a dilated segment, which again gradually 

 passes into the healthy part of the vessel (A. fusiforme), or 

 only a short segment of the vessel is sacculated (A. sacciforme). 

 In the latter case the sacculation either affects the entire cir- 

 cumference of the vessel (A. sacciforme periphericum s. axiale) 

 or only a part of it (A. sacciforme semiperiphericum). The 

 sacculated bulging may reach in horses the size of a man's head 

 (Labat & Cadeac), in dogs the size of a turkey's egg (Barrier). 

 The wall of the aneurysm is usually thickened, although in 

 places it. may be thinned out, owing to compression by neigh- 

 boring organs or from other causes. The thiekening of the wall 

 may be aided by layers of fibrin, which are sometimes deposited 

 on its inner surface, and these may entirely obliterate the lumen 

 of smaller vessels. 



The adjoining organs are crowded aside by the constantly 

 increasing aneurysm or they are compressed. Usually the 

 trachea or a bronchus are found compressed, one or more ver- 

 tebral bodies atrophic, the Vagus or the N. Eecurrens com- 

 pressed. Loosened portions of fibrin are carried away with the 

 blood and are usually arrested in the vessels of the posterior 

 half of the body. 



The bursting of an aneurysm almost always leads to fatal 

 internal hemorrhage. The break may occur into the cavity 

 of the thorax or into the abdominal cavity, or the blood may 

 be poured into a contiguous organ to which. the aneurysm had 

 become adherent. In this manner hemorrhages may take place 

 into the bronchi, the lungs, the stomach, the intestine or between 

 the layers of the mesentery. 



Symptoms. The symptoms of aortic aneurysm in animals 

 have in the past not been observed with sufficient exactness. In 

 the majority of cases the reports mention only increasing 

 emaciation and weakness or sudden fatal internal hemorrhage: 



Owing to the anatomical conditions only aneurysms which 



