The serratus posticus superior muscle (lat: Serratus posticus superior) - named from its saw-like edge and its relation to the other serrati - is a quadrilateral sheet with a toothed outer margin.
Origin
- The outer surface of the lower part of the ligamentum nuchas in its posterior edge;
- the spines of the last cervical and first two thoracic vertebra and the supraspinous ligaments connecting them.
Insertion
The upper borders and outer surfaces of the second to the fifth rib external to their angles.
Structure
The inner half is a tendinous sheet, the fibres of which run downwards and outwards and when they have passed beyond the line of the transverse processes they become fleshy and are inserted into the ribs by the lower borders of % four teeth into which the muscle divides.
The Third and Fourth Layers of the Muscles of the Back.
Nerve-supply
From the second and third intercostals by fine filaments which enter the outer part of its deep surface.
Action
To raise the ribs into which it is inserted; and therefore to assist in the inspiration.
Relations
Superficially, the trapezius, levator anguli scapulae, rhomboideus minor and major; deeply, the vertebral aponeurosis which separates it from the splenius and the more superficial spinal muscles; farther outwards the muscle covers part of the external intercostals.
Variations
The slips vary in number. Sometimes it gives off a slip from its upper border or posterior surface which goes to the levator angula scapulae, the mastoid process or the superior nuchal line.
