BY this heading I desire to consider especially certain anatomical points which are constantly obtruding themselves to our notice, and not always at the most opportune moment ; foremost among these are the relation of the cavity with-1. The Lateral Sinus or Fossa. 2. The Middle Cranial Fossa. 3. The Facial Nerve. 4. The Vestibule, etc. 1. The Lateral Simis. -Oi all, this structure or its fossa bears the least constant relationship to the antrum, and below will be found a series of woodcuts

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... ng its more usual variations. The method of preparation of these was by cutting sections of a number of bones, the saw-cut passing in a horizontal direction through the small fossa situated immediately superior to the supra-meatal spine, and I think more frequently present than the former. It may here be incidentally noted that this fossa is as good, if not from its greater constancy a better, guide to the antrum in opening this cavity than the spine. In the figures an asterisk denotes the fossa. Bones were only taken from adult skulls. Careful tracings were made from each. These were next compared by placing them one over another, and so six groups formed themselves, which allowed of a further reduction into three main groups, viz.-1. That class of skull in which the antrum must unavoidably be opened, or rather exposed, during operation on the antrum. 2. That in which it may or may not be seen during the operation. 3. That in which it will not come into view. FIG. 2. FIG. 3.