#Carotid Aneurysms.#--Aneurysm of the _common carotid_ is more frequent on the right than on the left side, and is usually situated either at the root of the neck or near the bifurcation. It is the aneurysm most frequently met with in women. From its position the swelling is liable to press on the vagus, recurrent and sympathetic nerves, on the air-passage, and on the œsophagus, giving rise to symptoms referable to such pressure. There may be cerebral symptoms from interference with the blood supply of the brain. Aneurysm near the origin has to be diagnosed from subclavian, innominate, and aortic aneurysm, and from other swellings--solid or fluid--met with in the neck. It is often difficult to determine with precision the trunk from which an aneurysm at the root of the neck originates, and not infrequently more than one vessel shares in the dilatation. A careful consideration of the position in which the swelling first appeared, of the direction in which it has progressed, of its pressure effects, and of the condition of the pulses beyond, may help in distinguishing between aortic, innominate, carotid, and subclavian aneurysms. Skiagraphy is also of assistance in recognising the vessel involved. Tumours of the thyreoid, enlarged lymph glands, and fatty and sarcomatous tumours can usually be distinguished from aneurysm by the history of the swelling and by physical examination. Cystic tumours and abscesses in the neck are sometimes more difficult to differentiate on account of the apparently expansile character of the pulsation transmitted to them. The fact that compression of the vessel does not affect the size and tension of these fluid swellings is useful in distinguishing them from aneurysm. _Treatment._--Digital compression of the vessel against the transverse process of the sixth cervical vertebra--the "carotid tubercle"--has been successfully employed in the treatment of aneurysm near the bifurcation. Proximal ligation in the case of high aneurysms, or distal ligation in those situated at the root of the neck, is more certain. Extirpation of the sac is probably the best method of treatment, especially in those of traumatic origin. These operations are attended with considerable risk of hemiplegia from interference with the blood supply of the brain.