In the consideration of bullet-wounds of the skull and brain the following factors must be taken into account:-- The velocity of the bullet. The distance at which the bullet is fired. The size of the bullet. The nature of the bullet. The angle of impact. The position of the bullet at the moment of impact. Before, however, noting the varying effects on the skull as produced by one or more of these factors, it will be necessary to allude briefly to the average effect on the skull as produced by bullet-wounds in general. ‘When a foreign body passes through any part of the skull--it matters not what the direction may be--the aperture of exit is always greater than the aperture of entry.’ Such was the law enunciated by Teevan in 1864. The explanation is as follows: ‘The aperture of entry is caused by the penetrating body only, whilst the aperture of exit is larger, insomuch as it is made by the penetrating body plus the fragments of bone driven out of the proximal table and diploe.’ It might also be added that the greater degree of damage will always be incurred by the unsupported table--the internal at the wound of entry, the external at that of exit. The size and shape of the aperture of entry through the external table bears a close resemblance to the size and shape of the entering bullet. As a general rule, it is round or oval, and presents clean-cut edges with some small radiating fissures. The aperture of entry through the internal table is larger, the margins inverted towards the brain, the radiating fissures more pronounced, and small fragments of bone in-driven towards the brain. In the event of perforation of the skull through the medium of a high-velocity bullet, the aperture of exit through the internal table closely resembles that through the external table at the site of entry, with the exception that it is influenced by any changes in position that the bullet may have undergone during its transmission through the brain. The wound of exit through the external table is again greater than that through the internal--in accordance with Teevan’s law--the margins everted, the surrounding bone fissured or comminuted, whilst fragments of bone may be driven out beneath the lacerated scalp, or even blown completely away. On the other hand, when the bullet is fired at close range, the aperture of exit is often considerably larger than that of entry--due, in all probability, to superadded explosive effect. The effect of the _velocity_ of the bullet on the fracture:--The greater the velocity of the bullet the greater the resemblance of the wounds of entry and exit to the size and shape of the bullet, the ‘cleaner’ the holes, and vice versa.