epaxial

Epaxial muscles include other (dorsal) muscles associated with the vertebrae, ribs, and base of the skull.

The epaxial muscle mass loses its segmental character to form the extensor muscles of the neck and trunk of mammals.

Each myotome divides into a dorsal epaxial part and a ventral hypaxial part.

The different families have 44-54 vertebrae, and there are three discrete bands of muscle tissue (epaxial, midlateral, and hypaxial) present in the caudal region.

The back of the skull is wide, with large projections on the exoccipital bones that would have anchored large epaxial muscles in the top part of the neck.

The myotome is divided into two sections, the epimere and hypomere, which form epaxial and hypaxial muscles, respectively.

The iliocostalis is the muscle immediately lateral to the longissimus that is the nearest to the furrow that separates the epaxial muscles from the hypaxial.

The Posterior lumbar aponeuroses are situated just on top of the epaxial muscles of the thorax, which are multifidus spinae and Sacrospinalis.

Epaxial muscles in humans are only the erector spinae and small intervertebral muscles, and are innervated by the dorsal rami of the spinal nerves.

Trunk muscles can be broadly divided into hypaxial muscles, which lie ventral to the horizontal septum of the vertebrae and epaxial muscles, which lie dorsal to the septum.

In humans, the erector spinae, the transversospinal muscles (including the multifidus, semispinalis and rotatores), the splenius and suboccipital muscles are the only epaxial muscles.

It is likely that the characteristically elongated neural spines were associated with well-developed epaxial muscles (muscles lying above the transverse process of the vertebrae) that facilitated lateral undulation in an axial subundulatory mode.

This bone inserts dorsally on the head and is capable of sliding forwards and backwards within a trough that extends the full length of the cranium and between the epaxial musculature on the front half of the body.

The dorsal ramus contains nerves that serve the dorsal portions of the trunk carrying visceral motor, somatic motor, and somatic sensory information to and from the skin and muscles of the back (epaxial muscles).

The lower or proximal portion of the spine has a rough surface that would have served as an anchoring point for the epaxial muscles of the back, and also has a network of connective tissues called Sharpey's fibers that indicate it was embedded within the body.

There is evidence for strong epaxial muscles along the base of the raised neural spines in both Sphenacodon and Dimetrodon, likely helping to stiffen and strengthen the backbone for walking and for lunging at prey by restricting side-to-side flexing motion.

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.