The small extent of skin actually destroyed is an important element in the rapid contraction often seen in these wounds when they progress favourably. Thus the large wound portrayed in fig. 48 contracted to one-fourth its original size ten days after the diagram and measurements were made. The large mass of protruded tissue was often most striking when a muscle such as the biceps in fig. 48 had been divided; but the herniae were more persistent when the mass projected in regions where tendons formed a large integral constituent, as at the wrist or lower third of the forearm. The protruding tissues naturally consisted of many varieties, according to what lay in the track of any particular wound. It should be added that for 'explosive' features to reach their strongest development, it is necessary that the bone affected should lie near the surface of the body; hence the most characteristic explosive wounds were met with in the forearm or leg, over the metacarpus or metatarsus, or in the arm. In the thigh, on the other hand, where the femur in a great part of its course not only lies deeply, but is also protected by particularly strong and resistent skin and fascia, another type of wound was met with. The explosive exit aperture, although large, was still only moderate in extent, sometimes, as in the front of the lower third, exposing a somewhat angular large track walled by the divided quadriceps extensor cruris. In other cases, on introducing the finger through a moderate exit opening on the inner aspect of the thigh, a large cavity, sometimes 4 or 5 inches in diameter, was discovered, full of clot and shreds of destroyed tissue and lined by a layer of similar material. In either of these latter cases the fractured bone ends were situated too deeply to take part in the actual laceration of the skin, while the force transmitted to the bone fragments, although sufficient to cause them to widely destroy the first soft tissues met with, did not suffice to cause them to burst or lacerate the skin widely. [Illustration: FIG. 48.--(22) 'Explosive' Exit Wound of front of Arm. Wound actual size eight days after its infliction. The prominences in the upper and lower parts correspond with the lacerated biceps. The dark crater led down to the fracture. In another week the wound had contracted to half the size. The entry aperture was a normal circular one. The arm a year later was used in the patient's employment as a hammer-man.] With regard to the theories of the production of these phenomena, that of the transmission of a part of the force of the bullet to the comminuted fragments, which thus themselves acquire the characters of secondary projectiles, seems quite adequate.[18] Examination of any of the skiagrams in which considerable comminution has taken place, shows that the fragments are carried forward and perforate the tissues distal to the fracture.