1. Biopsies of muscle were taken during the course of operation from sixteen patients with vascular injuries to the limbs. Three types of histological change were found.

2. In the first, there was massive necrosis of muscle fibres—a group of cases in which there had always been serious damage to the main artery of the limb or to the vessel supplying the affected muscles.

3. In the second type there was dense interstitial fibrosis, the muscle fibres sometimes being normal and sometimes showing necrosis or denervation—a group of cases in which the vascular injury varied from severance of the vessels by gunshot wounds to trivial damage, causing slow haemorrhage within fascial-bound spaces.

4. The third type showed scattered foci of necrosis together with patchy interstitial fibrosis—due to the pressure of tight plasters, crushing of the limb, fractures with arterial contusion, or slow haemorrhage or extravascular transfusion within fascial planes. The rise of tension within the muscles was probably sufficient to occlude the smaller arterioles with resultant patchy necrosis.

5. The vulnerability of certain muscles to vascular damage is partly related to the intramuscular vascular pattern, of which five types have been described.

6. In ischaemic muscles the intramuscular nerve trunks may be normal or they may show evidence of degeneration or necrosis; but in favourable circumstances there may be regeneration of axons.

7. In some cases there was evidence of regeneration of muscle fibres in man, the regeneration being dependent to some extent upon the efficiency of intramuscular anastomoses.

8. The prognosis, in cases of ischaemia of human voluntary muscle, depends upon the extent and the reversibility of damage to both muscle and nerve fibres and upon the extent of regeneration of muscle fibres.