These effusions are to be distinguished from the _cephal-hæmatoma_, in which the blood collects between the pericranium and the bone. This is oftenest seen in newly born children as a result of pressure on the head during delivery, and is characterised by its limitation to one particular bone--usually the parietal--the further spread of the blood being checked by the attachment of the pericranium at the sutures. Occasionally a permanent thickening of the edges of the bone remains after the absorption of the extravasated blood. This condition is to be diagnosed from traumatic cephal-hydrocele (p. 390). #Wounds of the Scalp.#--So long as a scalp wound, however extensive, is kept free from infection, it involves comparatively little risk, but the introduction of organisms to even the most trivial wound is fraught with danger, on account of the ease and rapidity with which the infection may spread along the emissary veins to the meninges and intra-cranial sinuses. The deeper the wound, the greater is the risk. If the epicranial aponeurosis is divided, the "dangerous area" between it and the pericranium is opened, and if infection occurs, it may lead to widespread suppuration. Should the wound extend through the pericranium, infection is more liable to spread to the bone and to the cranial contents. The usual varieties of wounds--incised, punctured, contused, and lacerated--are met with in the scalp, and they vary in degree from a simple superficial cut to complete avulsion. For medico-legal purposes it is important to bear in mind that a scalp wound produced by the stroke of a blunt weapon, such as a stick or baton, may closely simulate a wound made with a cutting instrument. On account of the density of the integument and its close connection with the aponeurosis, scalp wounds do not gape unless the epicranial aponeurosis is widely divided. This facilitates union in incised wounds, but interferes with drainage in the long narrow tracts which result from punctures, and which are so liable to be infected and to implicate the sub-aponeurotic space, the pericranium, or even the bone. It also favours the inclusion in the wound of a foreign body, such as the broken point of a knife, or a piece of glass. The bleeding from scalp wounds is often profuse and difficult to control, because the vessels, fixed as they are in the dense subcutaneous tissue, cannot retract and contract so as to bring about the natural arrest of hæmorrhage, and it is difficult to apply forceps or ligatures to their cut ends, suture ligatures are more efficient. On account of the free arterial anastomosis in the deeper layers of the integument, large flaps of scalp will survive when replaced, even if badly bruised and torn, and it is never advisable to cut away any un-infected portion of the scalp, however badly it may be lacerated or however narrow may be the pedicle which unites it to the head.