Rectus abdominal muscle

The rectus abdominis muscle is a paired, long, strap-like muscle located on either side of the linea alba, running from the sternum and costal cartilages cranially to the pubis caudally. It is part of the ventral abdominal wall musculature and is enclosed in the rectus sheath formed by the aponeuroses of the other abdominal muscles..

• Origin: From the sternum and costal cartilage.

• Insertion: Unites with the tendon of origin of the pectineus muscle and the prepubic tendon.

• Action: Along with other abdominal muscles, compression of the abdominal viscera. This action, known as abdominal press, aids in such vital functions as expiration, urination, defecation, and parturition. Flexion of the vertebral column when fellow muscles contract. Lateral bending of the vertebral column.

• Nerve: Medial branches of the intercostales and medial branches of the costoabdominalis, iliohypogstricus and ilioinguinalis.

• Blood Supply: cranial and caudal epigastric arteries:

Origin and Insertion

• Origin: Varies slightly by species, but generally arises from the sternum and adjacent costal cartilages. In carnivores and ruminants, the muscle often originates from the first few sternebrae (typically the first to the sixth).

• Insertion: nserts on the prepubic tendon and pecten ossis pubis via the tendon of insertion, often blending with the accessory ligaments of the prepubic tendon.

Structure and Fiber Direction

• The muscle fibers run parallel and longitudinally from cranial to caudal.

• Intersected by tendinous inscriptions (intermediate tendons), especially evident in dogs and horses, which segment the muscle into muscular bellies.

• Enclosed in a rectus sheath formed by the aponeuroses of the external oblique (superficial), internal oblique (partly superficial and partly deep), and transversus abdominis (deep).

• The linea alba is a fibrous raphe at the midline between the paired rectus muscles.

Function

• Supports the abdominal viscera.

• Aids in expiration, defecation, urination, parturition, and flexion of the vertebral column (especially in the lumbosacral region).

• Assists in abdominal press, particularly important in ruminants and parturient females.