DISEASES OF ABTEEtES 265 



WJiM is a dissecting aneurism ? 



Here the internal arterial coat gives -way usually at a 

 point which has undergone atheromatous changes. The blood 

 enters at this point, burrows along through the middle coat, 

 finds in its course another atheromatous patch, and thus 

 either reenters the current or extravasates into the surround- 

 ing adventitia. 



W hat is an aneurismal varix ? 



A direct communication with an artery and vein. 

 What are the causes of aneurisms ? 



The most common cause in the horse is a pin worm, the 

 strongylus armatus, giving rise to a verminous aneurism in 

 the mesenteric arteries, especially the anterior mesenteric 

 artery, where the parasite produces a chronic deforming 

 endarteritis and as a result of this an aneurism, also emboli 

 and degenerative changes in the arterial coats, as a result of 

 which the resisting power becomes limited, thus predisposing 

 to an aneurism when the blood pressure becomes excessive, 

 as by violent efforts, sudden strains, etc.; finally, traumatisms,, 

 as punctures. 



Are aneurisms often seen in animals ? 



Aneurisms of surgical interest are quite rare, and of all 

 animals the horse exhibits them most frequently. 



In which arteries of the horse are aneurisms of surgical 

 interest ? 

 Submaxillary, carotid, nasal, brachial, aorta, iliac and. 

 femoral arteries. 



Which symptoms do aortic aneurisms give rise to ? 



In the horse, aneurisms attaining the size of a man's 

 head are occasionally seen at the origin of the common aorta. 



