“I have long been dissatisfied with the account in standard works of the muscular action in animal locomotion”, Thomas Eakins writes at the beginning of “The Differential Action of Certain Muscles Passing More Than One Joint”. The essay, published by the Academy of Natural Sciences of Philadelphia, goes on to describe how its author jerry-rigged a plywood model of a horse’s leg — complete with catgut tendons and rubber bands for muscles — to better understand the relationships between its parts. Eakins also mentions dissecting both a live horse and a dead one for the same purpose, but leaves to the reader’s imagination whether or not the unfortunate creature(s) in question are in fact one and the same, on two separate sides of this mortal coil. The image above, ca. 1885, shows a young man, presumably Eakins’ assistant, canted over a horse’s severed leg, testament perhaps to the power of this animal’s musculature even when dead and dissected. More than a merely scientific image, there is an artistry to this composition (however grim), its play of lines and force, the way that the glass negative almost seems to x-ray all bodies equally.

That Eakins would be keenly interested in the push-pull of muscles under skin should come as no surprise to anyone acquainted with his artistic œuvre — whether in the form of surgical scenes, tangling wrestlers, or his many depictions of scullers pulling their needlelike vessels through the water. It was an intellectual curiosity that he would develop not only in his energetic canvas works but also via a series of images that might once have served as illustrations for his lectures on anatomy. In 1884, with funding from the University of Pennsylvania, the celebrated photographer Eadweard Muybridge came to Philadelphia to continue his groundbreaking studies of animal locomotion. A lecturer at the Pennsylvania Academy of Fine Arts (PAFA), Eakins formed part of an academic advisory board appointed to oversee the project. But while he initially dove into the undertaking with great interest, Eakins soon broke with his supervisee over a disagreement about methodology. This methodological rift led him to produce his own series of photos with the goal of capturing the sub-motions that make up each motion, from a woman’s walk to a pole vaulter's leap to the jiggering of a horse’s leg back and forth. In a series of images from PAFA’s collection, we even see that the grid that the artist used to provide a frame of reference has jumped off the page and onto the flanks of the horses themselves. Viewers today can appreciate Eakins’ studies as stirring and strange works of art — provided they can get past the prospect of flayed limbs.