It is barely possible to enter into the =operative details= suited to frontal and aural exostoses--the operations are so atypical. It is sufficient to say that the operation may be a very formidable one, that the details must be carefully thought out, and that every precaution must be adopted to avoid injuring neighbouring structures. [Illustration: FIG. 94. AN EXOSTOSIS OF THE ORBIT.] SARCOMATA, PRIMARY AND TRAUMATIC Primary sarcomata of the skull, when compared to sarcomata developing in other situations, is undoubtedly a rare disease. Still, many cases have been recorded, and four have come under my own personal care, one of which is depicted in the figure. The disease is equally prevalent in the two sexes, and, excluding chloromata (see p. 334), usually develops at or after middle life. The growth may originate in the diploic tissue (as a myelogenous tumour), or may spring from the pericranium. The cellular structure varies accordingly. More commonly the cells are of the large round or spindle type, and are proportionately malignant. As regards site of development, the temporal bone (squamous portion) is most commonly involved, next to which comes the frontal bone. In considering the ætiology of sarcoma in general, _trauma_ must always be taken into account, for it is an undoubted fact that it plays an important part in the development of this dire disease. With respect to the skull similar factors come into play. For instance, Fröhlking,[79] after collecting 48 cases of sarcoma of the skull, found a definite history of trauma in 9-21 per cent. [Illustration: FIG. 95. AN EXTRINSIC SARCOMA OF THE SKULL.] Ziegler[80] lays down the following essentials in establishing the traumatic origin of the tumour: It must develop directly after the trauma on the basis of the swelling or directly in the scar of the wound. The tumour must be palpable immediately after the acute swelling has diminished. At the site of the trauma constant or intermittent pain must be present. A considerable number of cases of sarcoma of the skull will fulfil even these arbitrary conditions. Such sarcomata may definitely be labelled ‘traumatic’ sarcomata.