Clawing of the ring, forefinger and little fingers is characteristic of an ulnar nerve lesion. Ulnar nerve lesions can also produce wasting of the hypothenar eminence and dorsal interosseous muscles. The latter causes "guttering" between the extensor tendons on the back of the hand. Ulnar lesions also cause loss of sensation to the back of the little finger and half of the ring finger.Sensation on the back of the thumb is provided by the radial nerve.Sensation on the palmar side of the forefinger is provided by the median nerve. Wasting of the thenar eminence is associated with lesions of the median nerve.