Overview
The epaxial muscles form three parallel columns, from lateral to medial:
- Iliocostalis (m. iliocostalis): from the ilium and lumbar vertebrae to the ribs.
- Longissimus (m. longissimus): the largest, from the ilium to the skull, between the transverse and spinous processes.
- Transversospinalis (m. transversospinalis): short bundles next to the spinous processes (spinalis, semispinalis, multifidus, rotatores).
The model shows the three columns as a single mass, from the ilium to the axis; in the neck it also stands for the deep dorsal neck muscles. The cat has no nuchal ligament, so these muscles alone hold up the head.
Origin and insertion
Ilium, sacrum, vertebral processes and ribs; each bundle spans one or several segments.
Action
Extend and stabilise the vertebral column. Acting on one side only, they bend it laterally. In leaping and galloping, extension of the spine lengthens each stride.
Innervation
Dorsal branches of the spinal nerves.
Clinical relevance
- The lumbar epaxial muscles are, with the quadriceps, a common intramuscular injection site in the cat.
- Feline injection-site sarcoma can infiltrate these muscles along fascial planes. Surgery needs wide margins (about 5 cm laterally and two fascial planes deep), sometimes including the dorsal spinous processes.
- Their bulk is palpated for muscle condition scoring: atrophy is an early sign of chronic disease (chronic kidney disease, hyperthyroidism) and of sarcopenia in older cats.
- Generalised muscle weakness (hypokalaemic myopathy, thiamine deficiency, myasthenia gravis) shows in the cat as ventroflexion of the neck.