A little anatomical knowledge will prevent us from being deceived, and enable us to make due allowances. There are no great difficulties in making a correct estimate, and the anatomists who have taught their pupils that correct cranial observations could not be made, only showed their own ignorance of the subject. We must consider the cranium as though all osseous protuberances had been shaved off, leaving the smooth, curving contour of the skull. The principal projection to be removed is the superciliary ridge corresponding to the brow at the base of the forehead. It is formed by the projection of the external plate of the skull, leaving a separation or cavity between it and the inner plate, which cavity is called the frontal sinus, and is sometimes half an inch wide. As there is no positive method of determining its dimensions in the living head, there must ever be some doubt concerning the development of the perceptive organs which it covers. The superciliary ridge at the external angle of the brow extends really as much as three-quarters of an inch from the brain. From this angle a ridge of bone (the temporal arch) extends upward and backward, separating the lateral surface of the head from the frontal and upper surfaces. This ridge is a convenient landmark, but must be excluded from an estimate of development as it is merely osseous. It extends back on the head a little behind its middle. The sagittal suture on the median line of the upper surface usually presents a slight, bony elevation or ridge (see the engraving of the skull, Chapter III.), and the lambdoid suture on the back of the head is frequently rough. A superficial practical phrenologist (of great pretensions) at Cincinnati, in examining the head of a gentleman of mild character, found the lambdoid suture quite rough, and gave him a terrifically pugnacious character, not knowing enough to distinguish between osseous and cerebral development. The occipital knob on the median line between the cerebrum and cerebellum, has been already mentioned. The mastoid process, the bony prominence behind the ear is a projection exterior to the cerebellum. Where it starts from the cranium above and behind the cavity of the ear, we may judge of basilar development by the breadth of the head, but the basilar depth which is more important is to be judged by the extension downward, which was illustrated in the last chapter by comparing the skulls of J. R. Smith and the slave-trading count. To judge the comparative strength of the higher and lower elements of character, we look for the height above the forehead and the depth at and behind the ear, which is ascertained by placing the hand on the base of the cranium behind the ears, while the height of the head is best appreciated by placing a hand on the top with the fingers reaching down to the brow.