In cases where the pad of the heel has been destroyed by disease or accident, so as to be partially or entirely unavailable for the flap, the late Dr. Richard Mackenzie[41] practised the following operation by internal flap:--With the foot and ankle projecting from the table with their internal aspect upwards, he entered the point of the knife (Plate I. fig. 14) in the mesial line of the posterior aspect of the ankle, on a level with the articulation, carried it down obliquely across the tendo Achillis towards the external border of the plantar aspect of the heel, along which it is continued in a semilunar direction. The incision is then curved across the sole of the foot, and terminates on the inner side of the tendon of the tibialis anticus, about an inch in front of the inner malleolus. The second incision (Plate III. fig. 4) is carried across the outer aspect of the ankle in a semilunar direction, between the extremities of the first incisions, the convexity of the incision downwards, and passing half an inch below the external malleolus. Precisely the same principle might supply the flap from the outer side in cases where the internal flap as well as the heel was deficient, but probably the nutrition of the external flap would be more doubtful. Neither the one nor the other is nearly so good as the true heel flap, and they are both only very poor substitutes for it when it cannot be had. The modification devised by Dr. Handyside does not seem to have any advantages over the original operation, and has not been adopted. The modification invented by Professor Pirogoff involves a much more important principle than any of the preceding. Instead of dissecting the flap from the posterior projecting portion of the os calcis, and removing the tarsus entire, he sawed off the posterior portion of the os calcis obliquely, leaving it in contact with the pad of skin, which is retained. Immediately after making the cut which defines the posterior flap and divides the tissues down to the bone, he opens the joint in front, disarticulates, and then putting on a narrow saw immediately behind the astragalus and over the sustentaculum tali, he saws the os calcis obliquely downwards and forwards till he reaches the first incision; then removes the ends of the tibia and fibula and brings up the slice of os calcis into contact with them. _Advantages._--It is easy of performance, saving the dissection from the heel, which some find so hard. It leaves a longer limb. It is said to bear pressure better, and there is certainly not so much chance of bagging of pus, and the mortality is exceedingly small, Hancock's collected cases giving only 8.6 per cent.; in cases of injury it is quite a warrantable operation.