Perforations of the lower extremity of the bone were very common. These were sometimes transverse and limited to the articular extremity itself, or the same limitation occurred to the antero-posterior tracks. These were the slightest forms of injury, putting on one side incomplete tunnels and grooves on the surface of the bone. With regard to the latter, however, when they invaded the joint cavity the injury was liable to be more severe than a complete perforation, in consequence of the projection of comminuted fragments into the joint cavity near the line of reflection of the synovial capsule and ulterior interference with freedom of movement. [Illustration: FIG. 55_a_.--Diagram of 'Butterfly' type.] [Illustration: PLATE XIV. Skiagram by H. CATLING. Engraved and Printed by Bale and Danielsson Ltd. (32) TYPICAL STELLATE (BUTTERFLY) COMMINUTED FRACTURE OF THE FEMUR Range 'short.' Wounds small, impact direct, very little fine comminution. The bone united without shortening of the limb.] Other tracks took a direction of longitudinal obliquity, and then implicated both epiphysis and diaphysis. Fig. 52, p. 169, shows an example, and also the peculiarity likely to be assumed by the exit aperture in the bone, especially if the bullet was travelling at a low rate of velocity, a considerable plate of the compact bone being driven out. In some cases these oblique tracks involved both femur and tibia. They will be referred to again under the heading of injuries to the joints, and some remarks will also be found there regarding the synovial effusion so often occurring into the knee-joint in cases of fracture of the shaft of the bone.