part of part of innervated by innervated_by develops from develops from musculature skeletal muscle of trunk epaxial myotome region mesoderm-derived structure musculature of trunk dorsal ramus of spinal nerve epaxial musculature the muscles derived from the medial myotome; includes the intrinsic back muscles XAO:0003229 UBERON:0008778 epaxial muscles Musculature that is derived from the epaxial myotome region, ventral to the horizontal septum of the vertebrae. Epaxial muscles include other (dorsal) muscles associated with the vertebrae, ribs, and base of the skull. The hypaxial muscles are located on the lower side of the body, often below the horizontal septum in many species (primarily fish and amphibians). In amniotes, the positional distinctions have been lost as the body's muscles have changed through evolution, but in all species, the hypaxial muscles are innervated by the ventral ramus of the spinal nerves, while the epaxial muscles are innervated by the dorsal ramus. Trunk muscles that lies dorsal to the horizontal septum.[AAO] In humans, the erector spinae, the transversospinal muscles (including the multifidus, semispinalis and rotatores), the splenius and suboccipital muscles are the only epaxial muscles AAO:0000142 EMAPA:37851 epaxial muscle