There have been conflicting descriptions of brachialis muscle anatomy in the literature. The purpose of the present study was to clarify brachialis muscle anatomy in order to refine surgical techniques around the elbow.Eleven cadaveric upper limbs were dissected under loupe magnification. The gross morphological characteristics, relationships, and nerve supply of the brachialis muscle were recorded. The nerve supply was examined histologically to confirm the gross findings.In all specimens, the brachialis muscle had two heads. The larger, superficial head originated from the anterolateral aspect of the humerus, proximal to the smaller, deep head. The superficial head contained longitudinal fibers, which inserted by means of a thick round tendon onto the ulnar tuberosity. The deep head fibers were fan-shaped and converged to insert by means of an aponeurosis onto the coronoid process. In all specimens, a branch of the radial nerve supplied the inferolateral fibers of the deep head.Our observations of brachialis muscle anatomy differ considerably from the descriptions in the current literature. The larger, superficial head has the mechanical advantage of a more proximal origin and a more distal insertion, which may enable it to provide the bulk of flexion strength. The smaller, oblique, deep head has a more anterior insertion on the coronoid, which may facilitate the initiation of elbow flexion from full extension. The radial nerve-innervated inferolateral fibers of the deep head run in a direction similar to the anconeus muscle, forming a muscular sling around the elbow. This complex may act to dynamically stabilize the ulnohumeral joint.This information may enhance surgical techniques about the elbow. The identification of an internervous plane may allow for improvement in the current anterior and anterolateral surgical approaches to the humerus. The tendon of the superficial head is well positioned to allow its transfer to the radial tuberosity, potentially improving supination strength in the absence of a distal biceps tendon. It is possible that the tendon of the superficial head might also be used to reconstruct the anular ligament or the medial collateral ligament of the elbow.