Epaxial and hypaxial muscles

Epaxial and Hypaxial Muscles are two distinct groups of muscles that are found in the body of vertebrates. They are derived from the myotome part of the somite, which is a structure formed in the early development of vertebrates.

Overview

The term "epaxial" refers to the muscles located above the horizontal septum in the body, while "hypaxial" refers to the muscles located below this septum. These muscles play a crucial role in the movement and support of the vertebrate body.

Epaxial Muscles

The epaxial muscles are located dorsally to the vertebral column. They are primarily responsible for the extension and lateral flexion of the vertebral column. The epaxial muscles are divided into three groups: the transversospinalis, the longissimus, and the iliocostalis.

Transversospinalis

The transversospinalis group is the most medial group of the epaxial muscles. It is further divided into the semispinalis, multifidus, and rotatores muscles.

Longissimus

The longissimus group is the intermediate group of the epaxial muscles. It is the longest and largest of the three groups.

Iliocostalis

The iliocostalis group is the most lateral group of the epaxial muscles. It is further divided into the iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis muscles.

Hypaxial Muscles

The hypaxial muscles are located ventrally to the vertebral column. They are primarily responsible for the flexion and lateral flexion of the vertebral column, as well as the movement of the limbs. The hypaxial muscles are divided into several groups, including the intercostal muscles, abdominal muscles, and limb muscles.

Intercostal Muscles

The intercostal muscles are located between the ribs and assist in respiration.

Abdominal Muscles

The abdominal muscles include the rectus abdominis, transversus abdominis, and the internal and external obliques.

Limb Muscles

The limb muscles include the muscles of the upper and lower limbs, which are responsible for the movement of the limbs.

See Also

• Muscular system
• Vertebral column
• Myotome
• Somite

References

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Epaxial and hypaxial muscles

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  Cross section of standard fish