The first 3 intercostal nerves are irregular and interesting: (a) the lateral and anterior cutaneous branches of the first intercostal nerve are small or wanting; (b) the lateral branch of the second runs across the dome of the axilla in the laminated fascia and then descends on the posteromedial aspect of the arm as the intercostobrachial nerve; (c) the lateral branch of the third sends a branch to the medial side of the arm.
Source: Boileau Grant JC. A Method of Anatomy: Descriptive and Deductive. 5th ed. Baltimore, Md: Williams & Wilkins Co; 1952:93.
September 2003. Arch Surg. 2003;138(9):970. doi:10.1001/archsurg.138.9.970