Trapezius

Origin: Occipital bone (back of the skull), ligamentum nuchae (nuchal ligament), and spinous processes of the cervical and thoracic vertebrae.

Insertion: Spine of the scapula, acromion, and lateral clavicle.

Action: The trapezius muscle is involved in movements of the scapula, including elevation, retraction, and rotation of the scapula.

Latissimus Dorsi

Origin: Spinous processes of the lower thoracic vertebrae, lumbar vertebrae, and iliac crest (back of the pelvis).

Insertion: Intertubercular groove of the humerus (upper arm bone).

Action: The latissimus dorsi muscle is responsible for shoulder extension, adduction, and medial rotation, as well as assisting in respiration.