SYNOPSIS. This essay is in two parts. The first describes functional studies of the shoulder in modern vertebrates that led to the formulation of the hypotheses that motor patterns of homologous muscles have been maintained during the evolution of the tetrapod shoulder, and that a primitive organization of the neural control components has persisted in derived groups. The second part of this essay focuses upon a longstanding question in vertebrate evolution: what neuromuscular and musculoskeletal changes in the tetrapod shoulder accompanied the evolution of flight in birds? The lack of empirical data on shoulder function in extant birds limited our insight into this question, and prompted our initiation of experimental studies. Preliminary kinematics of the furcula and humerus of European starlings (Sturnus vulgaris) flying in a wind tunnel, as revealed by high speed cineradiography, are presented. The two halves of the furcula, which contact the coracoids dorsally, are bent laterally during downstroke and medially during upstroke by as much as 60% of the intrafurcular resting distance. High speed film and electromyographic studies of freeflying pigeons (Columba livia) reveal that the supracoracoideus muscle is strongly activated during wing elevation and, as predicted from studies of Varanus and Didelphis, an additional activation burst occurs at mid-downstroke in 48% of the recordings.