
In adult
vertebrate
Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain.
The vertebrates make up the subphylum Vertebra ...
s, trunk muscles can be broadly divided into hypaxial muscles, which lie
ventral
Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
to the horizontal
septum
In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate.
Examples
Hum ...
of the
vertebrae
Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
and epaxial muscles, which lie
dorsal
Dorsal (from Latin ''dorsum'' ‘back’) may refer to:
* Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism
* Dorsal, positioned on top of an aircraft's fuselage
The fus ...
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 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 si ...
, the
transversospinales
The transversospinales are a group of muscles of the human back. Their combined action is rotation and extension of the vertebral column. These muscles are small and have a poor mechanical advantage for contributing to motion. They include: the th ...
(including the
multifidus
The multifidus (multifidus spinae; : ''multifidi'') muscle consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the vertebrae, from the sacrum to the axis. While very thin, t ...
,
semispinalis and
rotatores), the
splenius
The splenius muscles are:
*Splenius capitis muscle
*Splenius cervicis muscle
Their origins are in the upper thoracic and lower cervical spinous process
Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bo ...
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 language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate.
Examples
Hum ...
in many species (primarily fish and amphibians). In all species, the hypaxial muscles are
innervated
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called ...
by the
ventral ramus
The ventral ramus (: 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 nerve e ...
(branch) of the spinal nerves, while the epaxial muscles are innervated by the
dorsal ramus
The dorsal ramus of spinal nerve, posterior ramus of spinal nerve, or posterior primary division is the posterior division of a spinal nerve. The dorsal rami provide motor innervation to the deep (a.k.a. intrinsic or true) muscles of the back, and ...
.
References
Muscular system
{{Muscle-stub