In this discussion the term "arteriovenous aneurysm" is used to denote "any abnormal communication established between the arterial and venous channels" and includes, therefore, all direct and indirect communications variously spoken of as arteriovenous varix, varicose aneurysm, aneurysm by anastomosis, pulsating venous aneurysm and cirsoid aneurysm. These communications usually result from trauma to the vessels, such as piercing, incisive, lacerating, crushing or contusive wounds (cirsoid aneurysm of scalp is a notable example), and are known as acquired arteriovenous aneurysms; not infrequently they are produced by developmental anomalies, and are then termed congenital. The symptoms and systemic effects of the two types are essentially similar; the chief differences will be noted later. In the Mayo Clinic from January, 1915, to April, 1926, operation was performed in forty-one cases of arterial and arteriovenous aneurysm. Twenty-five of these were arteriovenous; sixteen were acquired and nine were congenital. In 1757, John Hunter first recognized