ation and a soft, whifling bruit, but they differ from an aneurysm
in that they are not diminished in size by compression of the main
artery, nor can they be emptied by pressure.

The exaggerated pulsation sometimes observed in the abdominal aorta, the
"pulsating aorta" seen in women, should not be mistaken for aneurysm.

#Prognosis.#--When _natural cure_ occurs it is usually brought about by
the formation of laminated clot, which gradually increases in amount
till it fills the sac. Sometimes a portion of the clot in the sac is
separated and becomes impacted as an embolus in the artery beyond,
leading to thrombosis which first occludes the artery and then extends
into the sac.

The progress of natural cure is indicated by the aneurysm becoming
smaller, firmer, less expansile, and less compressible; the murmur and
thrill diminish and the pressure effects become less marked. When the
cure is complete the expansile pulsation is lost, and there remains a
firm swelling attached to the vessel (_consolidated aneurysm_). While
these changes are taking place the collateral arteries become enlarged,
and an anastomotic circulation is established.

An aneurysm may prove _fatal_ by exerting pressure on important
structures, by causing syncope, by rupture, or from the occurrence of
suppuration. _Pressure_ symptoms are usually most serious from aneurysms
situated in the neck, thorax, or skull. Sudden fatal _syncope_ is not
infrequent in cases of aneurysm of the thoracic aorta.

_Rupture_ may take place through the skin, on a mucous or serous
surface, or into the cellular tissue. The first haemorrhage is often
slight and stops naturally, but it soon recurs, and is so profuse,
especially when the blood escapes externally, that it rapidly proves
fatal. When the bleeding takes place into the cellular tissue, the
aneurysm is said to become _diffused_, and the extravasated blood
spreads widely through the tissues, exerting great pressure on the
surrounding structures.

The _clinical features_ associated with rupture are sudden and severe
pain in the part, and the patient becomes pale, cold, and faint. If a
comparatively small escape of blood takes place into the tissues, the
sudden alteration in the size, shape, and tension of the aneurysm,
together with loss of pulsation, may be the only local signs. When the
bleeding is profuse, however, the parts beyond the aneurysm become
greatly swollen, livid, and cold, and the pulse beyond is c