_Adenomas_ originating in the sebaceous or sweat glands are sometimes multiple, of a purplish colour, and the skin covering them is thin and glistening. They show a tendency to ulcerate and fungate, giving rise to a fœtid discharge, and may be mistaken for epithelioma; they are also liable to become the seat of epithelioma. They are treated by excision. Large, flat _papillomas_ or warts may be single or multiple; they are of slow growth, and as they may also become the starting-point of epithelioma, they should be removed. [Illustration: FIG. 178.--Adenoma of Scalp.] The _plexiform neuroma_ forms a loose soft tumour situated in the course of one or more branches of the trigeminal nerve, especially the supra-orbital branch. In its most aggravated form the tumour hangs over the face or neck in large pendulous masses, and is described as a _pachydermatocele_ (V. Mott). A _sarcoma_ usually has its origin in the bones of the skull, and only implicates the scalp secondarily. _Epithelioma_ of the scalp may originate in relation to a wart, an ulcerated wen or sebaceous adenoma, or the cicatrix of a burn. It may affect comparatively young persons, may spread over a wide area, or pass deeply and involve the bone. Free and early removal is indicated. _Rodent cancer_ may originate on the scalp, but usually spreads thither from the face. In operating for extensive tumours of the scalp the hæmorrhage is sometimes formidable. It may be controlled by an elastic tourniquet applied horizontally round the head, or if, on account of the position of the tumour or from other causes, this is not practicable, by ligation or temporary clamping of the external carotid on one or on both sides. #Air-containing Swellings#--_Pneumatocele Capitis._--Cases have been recorded in which, as a result of pathological or traumatic perforations of the mastoid, and less frequently of the frontal cells, air has passed under the pericranium and given rise to a tense rounded tumour, resonant on percussion, and capable of being emptied by firm pressure. Such swellings exhibit neither pulsation nor fluctuation; and as they are painless, and give rise to almost no inconvenience, they do not call for treatment. _Emphysema of the scalp_ may follow fractures implicating any of the air sinuses of the skull, the air infiltrating the loose cellular tissue between the pericranium and the aponeurosis, and on palpation yielding a characteristic crepitation. It usually disappears in a few days. #Vascular Tumours.#--_Nævi_ on the scalp present the same features as elsewhere. If placed over one of the fontanelles, a nævus may derive pulsation from the brain, and so simulate a meningocele.