=Lines of cerebral sinuses.=--A line drawn over the head from the root of the nose to the occipital protuberance corresponds with the superior longitudinal sinus. Another line drawn from the occipital protuberance to the front border of the mastoid process corresponds with a part of the lateral sinus. =Middle meningeal artery.=--The trunk of the middle meningeal artery runs along the front lower corner of the parietal bone, about one inch and a half behind, and half an inch above, the external angular process of the frontal. A straight line drawn from the front of one mastoid process to the other would pass through the middle of the condyles of the occiput, showing how nearly the skull is balanced on the top of the spine in the erect posture. 6. =Thickness of skull-cap.=--The average thickness of the cap of an adult skull is about ⅕ of an inch. The thickest part is at the occipital protuberance, where it is often ¾ of an inch or more, even in an otherwise thin skull. The thinnest part is at the temple, where it may be almost as thin as parchment. Everyone in the habit of making post-mortem examinations knows how much the skull-cap differs in thickness in different persons and in different parts of the same skull. In old persons it is often in some parts not thicker than a shilling, owing to absorption of the diploë. Another point of interest is that the inner plane of the cap is not always parallel with the outer. Hence, in applying the trephine this is not a bad rule--‘Think that you are operating on the thinnest skull ever seen, and thinner in one half of the circle than the other.’ 7. =Levels of the brain.=--The level of the anterior lobes in front corresponds with a straight line drawn across the forehead, just above the eyebrows. The lower level of the anterior and middle lobes of the cerebrum corresponds with a line drawn from the external angular process of the frontal bone to the upper part of the meatus auditorius. Another line drawn from the meatus to the occipital protuberance corresponds with the lower level of the posterior lobe. The lower level of the cerebellum cannot be defined by external examination. It depends upon the extent to which the occipital fossæ bulge into the nape of the neck; and this bulge varies in different skulls. _THE FACE._ 8. The approaches to the organs of the senses, their ever-varying expression, their numerous muscles, and their rich profusion of vessels and nerves, give the face great anatomical importance, which has a most valuable bearing, not only on the practice of surgery, but on the physiognomy of health, and in the diagnosis of disease.