In. the skin we meet with all the three forms of vascular tumour already referred to - the venous, capillary, and cavernous. The ordinary naevus, which is in the form of a flat, more or less extensive area of a bright or bluish-red colour, consists essentially of enlarged veins. This seldom becomes prominent and is not erectile. It is a congenital lesion, and its origin has been ascribed to faulty union of the fcetal fissures, more especially the branchial clefts. According to Unna, however, it is due rather to pressure of the foetus against the more resisting maternal parts, especially in cases when the amnionic fluid is deficient. The capillary and cavernous angiomata are more prominent tumours. Whilst most!}', like the venous form, congenital in origin, these are liable to enlarge during extra-uterine life. In some cases the cavernous form, after many years of quiet existence, takes on a sarcomatous action, so as to form an angiosarcoma as shown in Fig. 482, in this respect showing analogies with the congenital soft wart. When this occurs the walls of the vascular spaces become highly cellular as shown in the figure. These cellular trabecular, it will be observed, have their own capillary vessels.

Fig. 482. - Angio-sarcoma of arm. There had been a cavernous angioma first noticed at ten years of age, but increasing gradually from the age of twenty-one. It. had grown more rapidly for the last four or five years. Before removal it formed a prominent erectile tumour. The patient was a man aged forty-five years, x 100.

The most frequent seat of the vascular naevus is the head, more particularly the eyelids, cheeks, ear, nose, and lips. According to Unna, they are present, often merely as slight marks, near the vertex of the head in from 10 to 20 per cent, of persons. They occur less frequently on the trunk and limbs.