The muscles of the superior limb arise from three different developmental primordia – the caudal branchial arches, the hypaxial body wall, and the limb bud. The first two groups, the branchial arches and body wall muscles, form attachments with the pectoral girdle and help stabilize and move the proximal end of the limb. The muscles of the limb proper (brachial, antebrachial, and hand muscles) and some of the shoulder joint muscles, which migrate secondarily back onto the trunk wall, are all derived from the embryonic limb bud. This is a highly varied group of muscles with a wide range of functions. The muscles range from large muscles that play major roles in supporting and stabilizing the limb, yet produce very small ranges of movement, to other muscles that produce the greatest range of movements in the entire body. Because of its diverse embryonic origins, the muscles of this group receive their nerve supply from different sources. Some of the muscles are supplied by cranial nerves (branchial arch muscles), another is innervated by body wall ventral rami (levator scapulae), and the remainder are supplied by the ventral rami that form the large brachial plexus that courses through the entire upper limb.
