In adult
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...
s, trunk muscles can be broadly divided into hypaxial muscles, which lie
ventral to the horizontal
septum
In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate.
Examples
Human anatomy
* Interat ...
of the
vertebrae
The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
and epaxial muscles, which lie
dorsal to the septum. Hypaxial muscles include some vertebral muscles, the
diaphragm
Diaphragm may refer to:
Anatomy
* Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen
* Pelvic diaphragm or pelvic floor, a pelvic structure
* Urogenital diaphragm or triangular ligament, a pelvic structure
Other
* Diap ...
, the abdominal muscles, and all limb muscles. The
serratus posterior inferior and
serratus posterior superior
The serratus posterior superior muscle is a thin, quadrilateral muscle. It is situated at the upper back part of the thorax, deep to the rhomboid muscles.
Structure
The serratus posterior superior muscle arises by an aponeurosis from the lo ...
are innervated by the
ventral primary ramus
The ventral ramus (pl. ''rami'') (Latin for ''branch'') is the anterior division of a spinal nerve. The ventral rami supply the antero-lateral parts of the trunk and the limbs. They are mainly larger than the dorsal rami.
Shortly after a spinal n ...
and are hypaxial muscles. Epaxial muscles include other (dorsal) muscles associated with the vertebrae, ribs, and base of the skull. In humans, the
erector spinae
The erector spinae ( ) or spinal erectors is a set of muscles that straighten and rotate the back. The spinal erectors work together with the glutes ( gluteus maximus, gluteus medius and gluteus minimus) to maintain stable posture standing or ...
, the
transversospinales (including the
multifidus,
semispinalis and
rotatores), the
splenius and
suboccipital muscles are the only epaxial muscles.
Hypaxial and epaxial muscles develop directly from
somitic cells. Differentiation of hypaxial and epaxial muscles is postulated to have evolved as a new trait in vertebrate animals.
Location
The hypaxial muscles are located on the ventral side of the body, often below the horizontal
septum
In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate.
Examples
Human anatomy
* Interat ...
in many species (primarily fish and amphibians). In all species, the hypaxial muscles are
innervated by the
ventral ramus (branch) of the spinal nerves, while the epaxial muscles are innervated by the
dorsal ramus.
References
Muscular system
{{Muscle-stub