They are ten or eleven pairs of small, flat, triangular musculo-tendinous fasciculi, which occupy the extreme upper ends of the intercostal spaces. They are blended with the external intercostals at their insertion.
Origin:Transverse process of thoracic vertebrae.
Insertion:Anterior borders of the succeeding rib.
Action:To aid in inspiration.
Blood supply:Intercostal arteries.
Nerve supply: Intercostal nerves.
Multifidus dorsi
It is a long muscle applied directly to the spinous processes of the vertebra from the sacrum to the neck. It consists of number of segments or bundles, which are directed forwards and upwards. It is continuous in front with the multifidus cervicis and behind with the sacro-coccygeus lateralis.
Origin:Lateral part of sacrum, oblique process of lumbar vertebrae and transverse processes of dorsal vertebrae.
Insertion:Posterior border of neural spines of lumbar and thoracic vertebrae in front.
Action:To extend the back and flex it to a side.
Blood supply: Intercostal and lumbar arteries.
Nerve supply: Dorsal and lumbar spinal nerves.
Intertransversales lumborum
These are small, flat muscles fill the inter-transverse spaces of the lumbar vertebrae.
Origin:The anterior border of the transverse process of the preceding lumbar vertebra.
Insertion:The posterior border of the transverse process of the lumbar vertebra in front.
