The effect of the larger size of the wedge provided by the bullet in increasing the length of secondary longitudinal fissures is well marked, and for the same reason the perforations are usually accompanied by fissures of considerable extent. It is interesting to note, however, that even in the case of the large bullets, and the special tendency shown by them to cause the extension of fissures into the joints, one or two specimens still show that these fissures incline to stop short when the point of junction between the portion of the shaft occupied by the medullary canal and that built on a foundation of cancellous tissue is reached. LESIONS OF THE SHORT AND FLAT BONES The above types of fracture are those common to the shafts of the long bones, but the difference in structure of the articular ends and the short and flat bones endows lesions of these with somewhat different characters, the nature of which varies between grooving, perforation, and great comminution. The most typical injury consists in the production of a clean perforation of the cancellous bone; this was common both in the articular ends and in the short bones. The tunnel differed little in character from those already described, a tendency always existing to the lifting of a lid of compact tissue at the exit end of the track. For the production of the cleanest forms of injury I believe high rates of velocity were distinctly favourable, although I am unable to maintain this statement by proof in the case of injuries received at the shortest ranges of fire. When the velocity was lower, yet with force still sufficient to produce a perforating injury, the separation of an extensive scale of bone at the exit aperture was a marked feature not seen in perforations produced by higher degrees of velocity. Fig. 52, of a perforation of the lower end of the femur, well exhibits this feature; but it must be borne in mind in this case that the illustration is not a pure one, both shaft and epiphysis taking part in the walls of the track, and the exit opening is in the former, where a thicker layer of compact bone exists than would cover any epiphysis, and hence the fragment is larger. I use the example, however, because it so forcibly illustrates the effect of increased resistance on the part of the bone struck in widening the area of the lesion. When the track was entirely limited to the articular ends the small amount of damage at either aperture was shown by clinical evidence in the rarity of subsequent limitation of joint movements due to bony deformity. [Illustration: FIG. 52.--Oblique perforation, implicating both epiphysis and diaphysis. Large fragment detached at exit aperture. Caused by a bullet travelling at a low rate of velocity. Compare with figs. 71 and 72 of a skull fracture. The dotted lines indicate the course of the track]