To command the femoral in Scarpa’s triangle, the pad of the tourniquet should be placed at the apex, and the direction of the pressure should be, not backwards, but outwards, so that the artery may be compressed against the femur. In the middle third of the thigh the femoral artery lies in Hunter’s canal, overlapped by the sartorius. About the commencement of the lower third the artery leaves the canal through the oval opening in the adductor magnus, and, under the name of popliteal, enters the popliteal space. The line for finding the artery in Hunter’s canal has been already traced (102). The incision to reach the artery in this part of its course would fall in with the outer border of the sartorius. To command the femoral artery in Hunter’s canal, the pressure should be directed outwardly, so as to press the vessel against the bone. _THE BUTTOCKS._ 103. =Buttocks.--Bony landmarks.=--The bony landmarks of the buttocks which can be distinctly felt are: 1, the posterior superior spines of the ilia; 2, the spines of the sacral vertebræ; 3, the two tubercles of the last sacral vertebra; 4, the apex of the coccyx in the deep groove leading to the anus; 5, the tuberosities of the ischia on each side of the anus. The posterior spines of the ilia are about the level of the second sacral spine, and correspond with the middle of the sacro-iliac symphysis. The third sacral spine marks the lowest level to which the membranes of the cord and the cerebro-spinal fluid descend in the spinal canal. The tuberosities of the ischia, in the erect position, are covered by the gluteus maximus. In the sitting position they support the weight of the body, and are only covered by a thick pad of coarse fat. Between this pad and the bones there is a bursa, which becomes occasionally enlarged and inflamed in coachmen. The prominence of the nates is one of the characteristics of man in connection with his erect attitude. ‘Les fesses n’appartiennent qu’à l’espèce humaine.’ They are formed of an accumulation of fat over the great muscle of the buttock (gluteus maximus). From their appearance we may gather some indication of the state of the constitution. They are firm and globose in the vigorous; loose and flaccid in the infirm. Wasting and flattening of one, compared with the other, is an early symptom of disease in the hip. 104. =Fold of the buttock.=--The deep furrow, termed ‘the fold of the buttock,’ which separates the nates from the back of the thigh, corresponds with the lower border of the gluteus maximus. Its altered direction in disease of the hip is very characteristic. This is the best place to feel for the great ischiatic nerve. We find it by pressing deeply between the trochanter and the tuber ischii, rather nearer to the latter. When we sit upright, the nerve is not liable to pressure; but it becomes numbed when we sit long sideways.