Overview
It has a costal and a lumbar part. Its fleshy part covers the lateral abdominal wall and the caudoventral thorax; ventrally it continues as an aponeurosis that reaches the linea alba. The model shows the fleshy part.
In the bovine flank it forms the outermost muscle layer of the paralumbar fossa, the hollow bounded by the last rib, the lumbar transverse processes and the tuber coxae. Deep to it lie the internal oblique and the transversus abdominis.
Origin
- Costal part: lateral surfaces of the caudal ribs, by digitations alternating with those of the serratus ventralis.
- Lumbar part: last rib and thoracolumbar fascia.
Insertion
Through its aponeurosis: linea alba, prepubic tendon and inguinal ligament.
Action
Compresses the abdomen (expiration, defecation, urination, parturition) and bends the trunk to the same side.
Innervation
Ventral branches of the caudal thoracic and cranial lumbar nerves. The skin and muscles of the flank depend mainly on nerves T13, L1 and L2.
Clinical relevance
- Flank laparotomy, in the standing animal, passes in turn through the external oblique, the internal oblique, the transversus abdominis and the peritoneum. Through the right flank displaced abomasum (right or left) is corrected with omentopexy; through the left flank rumenotomy and abomasopexy for left displacement are performed. Caesarean section is often done through the left flank.
- The flank wall is desensitised with paravertebral anaesthesia of nerves T13, L1 and L2 or with an inverted-L block.
- Its aponeurosis contains the superficial inguinal ring.