in the operation, in
which case the collateral circulation cannot be maintained after the
main vessel is tied. There is a danger, too, of injuring the middle
branch of the sciatic nerve, in the incisions required to reach the
artery; and, lastly, there is a possibility of this vessel dividing
higher up than usual. Considering these facts in reference to those
cases in which it might be supposed necessary to tie the popliteal
artery--such cases, for example, as aneurism of either of the crural
arteries, or secondary haemorrhages occurring after amputations of the
leg at a time when the healing process was far advanced and the bleeding
vessels inaccessible,--it becomes a question whether it would not be
preferable to tie the femoral, rather than the popliteal artery. But
when the popliteal artery itself becomes affected with aneurism, and
when, in addition to the anatomical circumstances which forbid the
application of a ligature to this vessel, we consider those which are
pathological,--such as the coats of the artery being here diseased, the
relative position of the neighbouring parts being disturbed by the
tumour, and the large irregular wound which would be required to isolate
the disease, at the risk of danger to the health from profuse
suppuration, to the limb from destruction of the collateral branches, or
to the joint from cicatrization, rendering it permanently bent,--we must
acknowledge at once the necessity for tying the femoral part of the main
vessel.

When the popliteal artery happens to be divided in a wound, it will be
required to expose its bleeding orifices, and tie both these in the
wound. For this purpose, the following operation usually recommended for
reaching the vessel may be necessary. The skin and fascia lata are to be
incised in a direction corresponding to that of the vessel. The extent
of the incision must be considerable, (about three inches,) so as the
more conveniently to expose the artery in its deep situation. On laying
bare the outer margin of the semi-membranosus muscle, while the knee is
straight, it now becomes necessary to flex the joint, in order that this
muscle may admit of being pressed inwards from over the vessel. The
external margin of the wound, including the middle branch of the sciatic
nerve, should be retracted outwards, so as to ensure the safety of that
nerve, while room is gained for making the deeper incisions. The adipose
substance, which is here generally abundant, s