Corpus: Obliquus externus muscle
Synonym: external abdominal oblique muscle
1. Definition
The obliquus externus muscle is a skeletal muscle that forms part of the lateral abdominal musculature.
2. Progression
2.1. Origin
The obliquus externus muscle originates from the outer surfaces of the 5th to 12th ribs. It runs in a caudal-medial direction towards its various insertion points, with its fibers oriented perpendicular to those of the obliquus internus muscle. This muscle, along with the serratus anterior muscle, contributes to the formation of the Gerdy line, an anatomical landmark where these muscle fibers interdigitate.
2.2. Attachment
The attachment tendon fibers of the obliquus externus muscle are divided into two parts: the medial and the lateral part. The lateral part attaches to the outer lip of the iliac crest, the inguinal ligament, and the pubic tubercle. The medial part contributes to the formation of the rectus sheath and inserts into the linea alba. The slit-like opening between these two parts forms the external inguinal ring of the inguinal canal.
3. Innervation
The obliquus externus muscle is innervated by the anterior branches of the spinal nerves from the thoracic spinal cord segments Th5-Th12.
4. Function
The obliquus externus muscle has several key functions:
- Rotation of the trunk: When contracted unilaterally, it rotates the trunk to the opposite side, especially when working in conjunction with the obliquus internus muscle on the opposite side.
- Lateral flexion: It inclines the thorax to the same side when contracted unilaterally, along with the obliquus internus muscle on the same side.
- Forward flexion: It participates in the forward flexion of the trunk.
- Pelvic tilt: It aids in lifting the front edge of the pelvis.
- Abdominal press and expiration: It contributes to the abdominal press and assists in forced expiration.