The muscle arises from four vertebral spines (T2-5), and the intervening supraspinous ligaments. Its insertion into the scapula extends from the inferior angle to the upper part of the triangular area at the base of the scapular spine; a fibrous arch receives the fibers of the muscle between these two points. The fibrous arch is often only loosely attached to the vertebral border of the scapula except at its ends.
This is a narrow ribbon of muscle parallel with the above, arising from two vertebral spines (C7, Tl) and inserted into the medial border of the scapula above the triangular area and below the attachment of levator scapulae.
Nerve supply of rhomboids:
By the dorsal scapular nerve (nerve to the rhomboids) from the C5 root of the brachial plexus which passes through scalenus medius, runs down deep to levator scapulae (which it supplies) and lies on the serratus posterior superior muscle to the medial side of the descending branch of the transverse cervical artery. It supplies each rhomboid on the deep surface.
Action of rhomboids:
The rhomboids draw the vertebral border of the scapula medially and upwards. They are antagonists to the rotatory action of trapezius; they contract with trapezius in squaring the shoulders, i.e. retracting the scapula.
Test. With the hand on the hip or behind the back the patient pushes the elbow backwards against resistance and braces the shoulder back. The muscles are palpated at the vertebral border of the scapula; being deep to trapezius they are not always visible. If the rhomboids of one side are paralyzed the scapula of the affected side remains farther from the midline than that of the normal side.