Topographical Anatomy of the Equine M. Cutaneus Trunci in Relation to the Position of the Saddle and Girth

The aim was to investigate the topographical anatomy of m. cutaneus trunci with reference to the position of the saddle and girth and its possible role in persistent sensitivity to girth pressure. The methodology involved dissections of 12 horse cadavers to describe the topography, attachments, morphological features, and thickness of the cutaneous muscles. M. cutaneus trunci was more variable in size and shape, especially the extent and curvature of its dorsal border, than the descriptions in anatomical texts indicate. In all horses, it extended far enough dorsally to lie directly underneath the weight-bearing panels of the saddle. The muscle was substantial in size, weighing 2.6-4.3 kg and having a 1.5- to 2.7-cm thickness in the girth region. Craniodorsally, it was adherent to the underlying fascia in the scapular region. Cranioventrally, m. cutaneus trunci had a distinct fascial attachment with the tendons of m. latissimus dorsi and m. teres major on the teres major tuberosity and the glenohumeral joint capsule. From this fascial attachment, the muscle fibers radiated caudally and were intimately connected to the skin by a diffuse fibrous network. Tactile stimulation of the skin overlying the cutaneous muscle is associated with a reflex muscular contraction that twitches the overlying skin (panniculus reflex). Failure to habituate to pressure of the tack in areas overlying the m. cutaneus trunci may result in continuous stimulation of the panniculus reflex, which could play a role in persistent sensitivity to girth pressure in some horses.