posterior cutaneous nerve of arm posterior cutaneous nerve of arm the posterior cutaneous nerve of arm (internal cutaneous branch of musculospiral, posterior brachial cutaneous nerve) is a branch of the radial nerve that provides sensory innervation for much of the skin on the back of the arm. it arises in the axilla. posterior cutaneous nerve of armcutaneous nerves of right upper extremity. ("post. brach. cutan." visible at center left.)detailsfromradial nerveidentifierslatinnervus cutaneus brachii posteriorta98a14.2.03.050ta26432fma44948anatomical terms of neuroanatomy it is of small size, and passes through the axilla to the medial side of the area supplying the skin on its dorsal surface nearly as far as the olecranon. in its course it crosses behind and communicates with the intercostobrachial.