The branch of the innervation for the extensor carpi radialis brevis muscle (ECRBm), has been used to re- establish muscle functions in the upper limbs of patients who have spinal cord injury, of the brachial plexus or its terminal branches. The origin of the ECRBm varies, and can originate from the trunk of the radial nerve (RN), from the deep branch of the radial nerve (DBRN), or from the superficial branch of the radial nerve (SBRN). In order to further complement the anatomy related to the origin and distribution of the ECRBm branch, 30 formolized upper limbs from Brazilian individuals, from the Universidad Estadual de Ciencias da Saude, Maiceió, Brazil were used. Through dissection, the muscle and its innervations was located, determining the origin of the branch as well as distribution. To determine biometry, a transversal reference line, which passed through the most prominent areas of the epicondyles of the humerus (BEL) was considered. The nerve for ECRBm originated from DBRN in 50 % of cases; from the main trunk of RN in 26.7 % and from SBRN in 23.3 %. The distance from the origin of the branch studied and the BEL was an average of 23 ± 12 mm; the distance from the first, second and third motor point to the BEL was 55 ± 17 mm, 66 ± 17 mm and 79±11 mm, respectively. The distribution of the innervation was classified in four types in relation to the motor points. The results are an important contribution to anatomical knowledge, as well as neurosurgery during nerve transfers to restore functions of damaged muscles in the upper limb.

KEY WORDS: Anatomy; Peripheral Innervation; Upper limb; Muscle Branches; Extensor Carpi Radialis Brevis Muscle.