=Seat of injury.=—A knowledge of the seat of injury from the passage of a ball involves diagnosis of its course, the depth of its penetration, the particular organs or structures injured, and the extent of the injuries to which they have severally been subjected. The course pursued by balls in wounds presents many features of interest. The depth of penetration, in connection with direction, becomes of great importance when there is question of one of the great visceral cavities being opened. This part of the subject, however, together with that of injuries to the viscera themselves, will be more conveniently considered when treating of gunshot wounds in their special relations to particular regions. In like manner, the diagnosis of the extent of injury in wounds complicated with fractures of the long bones will be best considered under gunshot wounds of the extremities. =Course of balls.=—Of the circuitous and unexpected directions pursued by bullets in their course through the human frame, which were formerly so common, we are not likely to see many instances in future warfare, when the rifle is the weapon chiefly employed. The conical shape of the ball and the force with which it is propelled have had the effect, among others already named, of changing this characteristic of the ball from the smooth–bored musket. The latter, bearing a force that scarcely carried it true to a mark at eighty yards, and usually receiving, as it left the firelock, an impulse which caused it to revolve on its axis at right angles with the line of flight, was deflected by the most trifling obliquity of surface, by the resisting obstacle of a bone, by tendons or the aponeuroses of muscles, or even by the elastic resilience of muscles themselves in a state of action, when the relative direction of their fibers was favorably placed to exert this influence. The Enfield cylindro–conoidal bullet, armed with a force that will carry it to a given spot distant one thousand yards or upwards, flies like an arrow, penetrates the softer tissues in a straight line, and on meeting bone, as before noticed, enters it like a wedge. When a bullet of this kind strikes an object point–blank, it is always the apex of the conical part which first meets the object struck; and, if sufficient resistance be met with, it is this apex which becomes first compressed and turned back. When it strikes a solid object lying nearly parallel with its line of flight, the ball is planed, as it were, from its apex toward its base. In a case before referred to—page 29—where a conical ball entered the loin of a soldier of the 19th Regiment, and was subsequently passed per anum, the apex of the bullet was found to be turned and bent round on itself, and the ball generally flattened. On examining carefully the convex surface of the convoluted apex, minute spiculæ of bone were observed to be impacted in its substance. It became evident, therefore, that the ball