126. Dorsal artery.—The line of the dorsal artery of the foot is from the middle of the ankle to the interval between the first and second metatarsal bones. The artery can be felt beating over the bones along the outer side of the extensor longus pollicis, which is the best guide to it.
127. Bursa.—The synovial sheath of the extensor longus pollicis extends from the front of the ankle, over the instep (apex of the internal cuneiform bone) as far as the metatarsal bone of the great toe. There is generally a bursa over the instep, above, or it may be, below, the tendon.
There is often a large irregular bursa between the tendons of the extensor longus digitorum, and the projecting end of the astragalus, over which the tendons play. There is much friction here. It is well to be aware that this bursa sometimes communicates with the joint of the head of the astragalus.
128. Plantar arteries.—The course of the external plantar artery corresponds with a line drawn from the hollow behind the inner ankle obliquely across the sole nearly to the base of the fifth metatarsal bone; from thence the artery turns transversely across the foot, lying (deeply) near the bases of the metatarsal bones, till it inosculates with the dorsal artery of the foot in the first interosseous space.
The course of the internal plantar corresponds with a line drawn from the inner side of the os calcis to the middle of the great toe.
129. Plantar fascia.—To divide the plantar fascia subcutaneously, the best place is about one inch in front of its attachment to the os calcis. This is the narrowest part of it. The knife should be introduced on the inner side; and the incision will be behind the plantar artery.
The subcutaneous section of the tendon of the abductor pollicis should be made about one inch before its insertion.
THE ARM.
130. Clavicle.—The line of the clavicle and the projection of the joint at either end of it can always be felt, even in the fattest persons. Its direction is not perfectly horizontal, but slightly inclined downwards, when the arm hangs quietly by the side. When the body lies flat on the back, the shoulder not only falls back, but rises a little, the weight of the limb being taken off. Hence the modern practice of treating fractures of the clavicle (in the early stage) by the supine position.
On the front surface of the clavicle, not far from its acromial end, there is in many persons of mature age a spine-like projection of bone. So far as I know, it has not been described. A gentleman, himself a surgeon, showed me an instance in his own person. He suspected it was an exostosis.