There are usually two rhomboid muscles (Latin: musculi rhomboidei) - rhomboid minor and rhomboid major, which belong to the superficial muscle group of the back that collectively connect the upper limb to the trunk. The rhomboid muscles are located in the upper back and participate in maintaining upper body posture and contribute to stabilizing the shoulder. Sometimes both rhomboid muscles are fused into a single muscle.
The rhomboid major (Latin: musculus rhomboideus major) is one of the superficial muscles of the back that connects the scapula with the vertebral column. It lies deep to the trapezius muscle and inferior to the rhomboid minor.
The rhomboid major arises from the spinous processes of the second to fifth thoracic vertebrae (T2 - T5).
The rhomboid major muscle inserts into the medial border of the scapula - from the inferior angle to the root of the spine of the scapula.
The rhomboid major acts upon the scapulothoracic joint: it pulls the scapula posteromedially, rotates the glenoid cavity inferiorly. It also supports the position of the scapula.
The dorsal scapular nerve (C4 - C5) provides motor innervation to the rhomboid major muscle.
The rhomboid minor (Latin: musculus rhomboideus major) is a small muscle of the upper back that connects the scapula to the spine. It lies deep to the trapezius, inferior to the levator scapulae, and superior to the rhomboid major.
The rhomboid minor typically arises from the nuchal ligament and spinous processes of the seventh cervical vertebra (C7) and the first thoracic vertebra (T1).
Fibers of the rhomboid minor insert into the root (medial end) of the spine of the scapula.
The actions provided of the rhomboid minor are the same as those of rhomboid major. This muscle also acts upon the scapulothoracic joint by pulling the scapula posteromedially, rotating the glenoid cavity inferiorly, as well as supporting the position of the scapula.
The dorsal scapular nerve (C4 - C5) innervates the rhomboid minor.
Along with the rhomboid major, this muscle also receives oxygenated blood from the dorsal scapular artery.