Generations of anatomists have studied the course and distribution of the peripheral nerves, until knowledge of their more obvious features has apparently reached finality. It is recognised that more can be learnt of their central connections and of the relation of the larger branches to the anterior and posterior roots. But the peripheral distribution of the nerves of the hand is regarded as one of the common- places of anatomy.
And yet, whenever an attempt is made to apply this knowledge to some case where one of these nerves has been divided, obvious facts remain unexplained, or accessory hypotheses must be invented to account for the apparent difficulties of each individual instance. The more carefully the condition of the affected part is examined, the less does the state of its sensibility correspond with the surgeon’s expectation. After he has successfully reunited the ends of the nerve, a careful examination only adds to the bewilder- ment of the conscientious observer. If, for instance, the median nerve is divided, all cutaneoussensibility is abolished over a considerable part of both the index and middle fingers. But over the palm, within the area supplied by the median nerve, sensation may be diminished only.
In a similar manner, division of the ulnar nerve produces complete insensibility of the little finger and of a variable portion of the ulnar border of the palm.
Cutaneous sensibility is only partially lost over the palm and that part of the ring finger usually assigned to the ulnar nerve. “When the surgeon or anatomist is asked why sensation is only partially lost, the usual answer is, “Because the nerves overap."