f this is impracticable, the artery is tied above and below the
communication; gangrene of the limb may supervene, and we have observed
a case in which the gangrene extended up to the junction of the middle
and lower thirds of the thigh, and in which recovery followed upon
amputation of the thigh.

#Popliteal Aneurysm.#--This is the most common surgical aneurysm, and is
not infrequently met with in both limbs. It is generally due to disease
of the artery, and repeated slight strains, which are so liable to occur
at the knee, play an important part in its formation. In former times it
was common in post-boys, from the repeated flexion and extension of the
knee in riding.

The aneurysm is usually of the sacculated variety, and may spring from
the front or from the back of the vessel. It may exert pressure on the
bones and ligaments of the joint, and it has been known to rupture into
the articulation. The pain, stiffness, and effusion into the joint which
accompany these changes often lead to an erroneous diagnosis of joint
disease. The sac may press upon the popliteal artery or vein and their
branches, causing congestion and oedema of the leg, and lead to gangrene.
Pressure on the tibial and common peroneal nerves gives rise to severe
pain, muscular cramp, and weakness of the leg.

The differential diagnosis is to be made from abscess, bursal cyst,
enlarged glands, and sarcoma, especially pulsating sarcoma of one of the
bones entering into the knee joint.

The choice of operation lies between ligation of the femoral artery in
Hunter's canal, and Matas' operation of aneurysmo-arteriorrhaphy. The
success which attends the Hunterian operation is evidenced by the fact
that Syme performed it thirty-seven times without a single failure. If
it fails, the old operation should be considered, but it is a more
serious operation, and one which is more liable to be followed by
gangrene of the limb. Experience shows that ligation of the vein, or
even the removal of a portion of it, is not necessarily followed by
gangrene. The risk of gangrene is diminished by a course of digital
compression of the femoral artery, before operating on the aneurysm.

_Aneurysmal varix_ is sometimes met with in the region of the popliteal
space. It is characterised by the usual symptoms, and is treated by
palliative measures, or by ligation of the artery above and below the
point of communication.

_Aneurysm_ in the #leg and foot# is rare. It is almo