112. =Popliteal bursa.=--The precise position of the bursa in the popliteal space, which sometimes enlarges to the size of a hen’s egg, is between the tendon of the inner head of the gastrocnemius and the tendon of the semimembranosus, just where they rub one against the other. The bursa is from one and a half to two inches long. When enlarged, it makes a swelling on the inner side of the popliteal space, which bulges and becomes tense when the knee is extended, and _vice versâ_. I examined 150 bodies with a view to ascertain how often this bursa communicates with the synovial membrane of the knee. There was a communication about once in five instances. This should make us cautious in interfering too roughly with the bursa when enlarged. 113. =Popliteal artery.=--The popliteal artery can be felt beating and can be compressed against the back of the femur, close to which it lies. But pressure, sufficient to stop the blood, should be firm, and should be made against the bone nearer to the inner than the outer hamstrings. The line of the artery corresponds with the middle of the ham. It lies under cover of the fleshy belly of the semimembranosus, and the outer border of this muscle is the guide to it. An incision down the middle of the ham would fall in with the vessel just above the condyles. 114. =Peroneal nerve.=--The peroneal nerve runs parallel with and close to the inner border of the tendon of the biceps. It can be felt in thin persons. There is a risk of dividing it in tenotomy of the biceps, unless the knife be carefully introduced from within outwards. Below the knee the nerve can be felt close to the fibula just below the head, and when pressed upon in this situation causes a sensation to run down its branches to the foot. _THE LEG AND ANKLE._ 115. =Bony points.=--The tubercle of the tibia (for the attachment of the ligamentum patellæ), the sharp front edge called the shin, and the broad flat subcutaneous surface of the bone can be felt all the way down. The inner edge can be felt too, but not so plainly. The lower third is the narrowest part of the bone and the most frequent seat of fracture. The head of the fibula is a good landmark on the outer side of the leg, about one inch below the top of the tibia and nearly on a level with the tubercle. Observe that it is placed well back, and that it forms no part of the knee-joint, and takes no share in supporting the weight. The shaft of the fibula arches backwards, the reverse of the shaft of the tibia. The fact of the bones not being on the same plane should be remembered in flap amputations. The shaft of the fibula is so buried amongst the muscles, that the only part to be distinctly felt is the lower fourth. Here there is a flat triangular subcutaneous surface, between the peroneus tertius in front, and the two peronei (longus and brevis) behind. Here is the most frequent seat of fracture.