The aim of this paper was to report the incidences of the anastomosis between deep branch of ulnar nerve and a branch of the median nerve commonly named Cannieu-Riché anastomosis (CRA) and thenar muscles innervation. The anatomical dissection of 80 limbs from 40 fresh adult cadavers were performed in the Department of Anatomy at the Medical School of the Catholic University of São Paulo. The incidence of CRA and thenar muscle innervation were studied. The CRA was found in all of the dissected hands (100 %). The abdutor pollicis brevis and the opponens pollicis muscle are innervated exclusively by median nerve in all dissected hands. The superficial head of flexor pollicis brevis was innervated by the median nerve in of 56 the hands (70 %), in 24 (30 %) it had double innervation (median nerve and deep branch of ulnar nerve). The deep head of flexor pollicis brevis were absent in 11 hands (14 %), in 52 hands (65 %), a double innervation was observed. In 14 (17.5 %) exclusively by deep branch of ulnar nerve and in 3 hands (3.6 %) exclusively by a branch of median nerve. The oblique head of adductor pollicis muscle was innervated only by deep branch of ulnar nerve in 66 hands (82 %) of dissected hands, 14 (17.5 %) had a double innervation. The transverse head of adductor pollicis was innervated exclusively by deep branch of ulnar nerve in 77 hands (96.4 %), and in 3 (3.6 %) had a double innervation. According to our study the pattern of innervation was more frequent in relation to the flexor pollicis brevis muscle and should be considered as a normal pattern, in that the superficial head receives innervation of branches of median nerve, and the deep head receives innervation of deep branch of ulnar nerve and branches of median nerve (dual innervation). The abductor pollicis brevis and opponens pollicis received innervation exclusively by median nerve. Both the oblique and transverse head of adductor pollicis exclusively by ulnar nerve. The RCA was found in all of the dissected hands (100 %).
KEY WORDS: Median nerve; Ulnar nerve; Hand/Innervation.