he subclavian, carotid, and
external iliac arteries. It is not applicable to cases in which there is
such a degree of atheroma as would interfere with the successful
ligation of the artery. The continuity of the artery may be restored by
grafting into the gap left after excision of the sac a segment of the
great saphena vein.

_Ligation of the Artery._--The object of tying the artery is to diminish
or to arrest the flow of blood through the aneurysm so that the blood
coagulates both in the sac and in the feeding artery. The ligature may
be applied on the cardiac side of the aneurysm--proximal ligation, or to
the artery beyond--distal ligation.

_Proximal Ligation._--The ligature may be applied immediately above the
sac (Anel, 1710) or at a distance above (John Hunter, 1785). The
_Hunterian operation_ ensures that the ligature is applied to a part of
the artery that is presumably healthy and where relations are
undisturbed by the proximity of the sac; the best example is the
ligation of the superficial femoral artery in Scarpa's triangle or in
Hunter's canal for popliteal aneurysm; it is on record that Syme
performed this operation with cure of the aneurysm on thirty-nine
occasions.

It is to be noted that the Hunterian ligature does not aim at
_arresting_ the flow of blood through the sac, but is designed so to
diminish its volume and force as to favour the deposition within the sac
of laminated clot. The development of the collateral circulation which
follows upon ligation of the artery at a distance above the sac may be
attended with just that amount of return stream which favours the
deposit of laminated clot, and consequently the cure of the aneurysm;
the return stream may, however, be so forcible as to prevent coagulation
of the blood in the sac, or only to allow of the formation of a red
thrombus which may in its turn be dispersed so that pulsation in the sac
recurs. This does not necessarily imply failure to cure, as the
recurrent pulsation may only be temporary; the formation of laminated
clot may ultimately take place and lead to consolidation of the
aneurysm.

The least desirable result of the Hunterian ligature is met with in
cases where, owing to widespread arterial disease, the collateral
circulation does not develop and gangrene of the limb supervenes.

_Anel's ligature_ is only practised as part of the operation which deals
with the sac directly.

_Distal Ligation._--The tying of the artery beyond