Abstract
1 . Voluntary activity of any given muscle in the hand is not an absolute indication of the state of the nerve which usually supplies it.
2. Significant variations in the standard pattern of innervation have been found in 20 per cent of 226 cases studied.
3. The pattern of innervation described in standard text-books occurred in only 33 per cent. of cases.
4. A striking variation is the supply of every thenar muscle by the ulnar nerve. In other cases the first dorsal interosseous muscle may be supplied by the median nerve.
5. In order to arrive at an accurate diagnosis when anomalous innervation is suspected, nerve blocks at appropriate levels are required.
6. Great care must be taken during operations to avoid damage to connections between the ulnar and the median nerves, especially in patients with anomalous innervation of the hand muscles.
