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. As a rule the acromio-clavicular joint forms an even plane. But there is sometimes a knob of bone at the acromial end of the clavicle; or it may be only a thickening of the fibro-cartilage, sometimes existing in the joint. In either case this relief might be mistaken for a dislocation, or even for a fracture. A reference to the other shoulder might settle the question. 131. =Bony points of the shoulder.=--We can distinctly feel the spine of the scapula and the acromion, more especially at the angle where they join behind the shoulder. This angle is the best place from which to measure in taking the comparative length of the arms. In some shoulders, though very rarely, there is an abnormal symphysis between the spine of the scapula and the acromion. There may indeed be two symphyses and two acromial bones, the acromion having two centres of ossification. These abnormal symphyses might be mistaken for fractures, until we have examined the opposite shoulder, which is sure to present a similar conformation.[9]