_Aperture of exit._--The wound of exit in normal cases offers far more variation in appearance than that of entry, this variation depending on several circumstances: first, the want of support to the skin from without, and such other factors as the degree of velocity retained by the travelling bullet, the locality of the opening, and the density, tension, and resistance offered by the particular area of skin implicated. When the range has been short and the velocity high, it is often difficult to discriminate between the two apertures. Both may be circular and of approximately the same size, and the only distinguishing characteristic, the slight depression of the margin of the wound of entrance, may be absent if any time has elapsed between the infliction of the injury and examination by the surgeon. One very strong characteristic if present is the general tendency of the margins, and even the area surrounding the exit wound itself, to be somewhat prominent. Fig. 16 shows this point, although the wound from which it was drawn had been produced thirty-six hours before death. The specimen was then hardened in formalin and still preserves its original aspect. This character is, however, more frequently displayed in wounds received at mean, or longer, ranges. In wounds produced by bullets travelling at the highest degrees of velocity it is often absent. [Illustration: FIG. 20.--Circular Entry back of arm; exit (bird-like) in anterior elbow crease] [Illustration: FIG. 21.--Circular Entry over patella. Starred exit of elongated form in popliteal crease] When the range of fire has been greater and the velocity retained by the bullet lower, slit wounds are common, or some of the slighter degrees of starring. Actual starring I never saw, but reference to figs. 20 and 21 will show a tendency in this direction, also a close resemblance to the starred wounds resulting from perforations by large leaden bullets. Such wounds, I believe, are usually the result of a somewhat low degree of velocity. Slit exit wounds may be vertical or transverse (fig. 20) in direction, and the production of these is dependent on the locality in which they are situated, the thickness, density, and tension of the skin, and the nature of the connection of the latter with the subcutaneous fascia in the locality. Thus in wounds of different parts of the hairy scalp, so little variation exists in the relative density and structure of the skin, that, in spite of the want of external support at the aperture of exit, it is often difficult to discriminate offhand the two apertures, if neither bone nor brain debris occupies that of exit.