M. transversus abdominis, pars lumbalis (segmentum I)
The first lumbar segment of the transversus abdominis, originating from the transverse process of the 1st lumbar vertebra. The lumbar part forms the deep layer of the flank.
Origin: Transverse process of L1
Insertion: Linea alba via aponeurosis
Action: Compresses abdominal viscera; stabilizes the lumbar spine; assists forced expiration
Innervation: Ventral branches of thoracic (T10–T18) and lumbar (L1–L3) spinal nerves
Strain or tearing of the transversus abdominis fibers, often from sudden exertion, rolling, or trauma. Being the deepest layer, injuries here can compromise the entire abdominal wall integrity.
Strain or tearing of the transversus abdominis fibers, often from sudden exertion, rolling, or trauma. Being the deepest layer, injuries here can compromise the entire abdominal wall integrity. Signs include: Focal pain on deep palpation of the flank; guarding during lateral flexion; ventral edema; ultrasonographic evidence of fiber disruption or hematoma between muscle layers.
See the Transversus Abdominis - Lumbar Part, Segment I on our interactive 3D horse model. Open 3D Model