301 301 302 302 303 303 ## Muscles 304 304 305 305 The two most superficial muscles of the shoulder are the tra-pezius and deltoid muscles (Table 7.1 and Fig. 7.35). Together, they provide the characteristic contour of the shoulder: 306 306 307 307 The trapezius attaches the scapula and clavicle to the trunk. 308 308 309 309 The deltoid attaches the scapula and clavicle to the humerus. 310 310 311 311 312 312 ![A diagram labels anatomical features including the trapezius, acromion, spine of the scapula, clavicle, deltoid, and deltoid tuberosity of humerus.](https://cdn.orris.care/cdss_images/1f28e3feb87300c94865942a27f1e54f08b40155c9c2d647c1ff93ff6281a14f.png) 313 313 314 314 *Fig. 7.35 Lateral View of Trapezius and Deltoid Muscles.* 315 315 316 316 317 317 318 318 *Table 7.1 Muscles of the shoulder (spinal segments in bold are the major segments innervating the muscle)* 319 319 320 320 321 321

Muscle	Origin	Insertion	Innervation	Function
Trapezius	Superior nuchal line, external occipital protuberance, medial margin of the ligamentum nuchae, spinous processes of CVII to TXII and the related supraspinous ligaments	Superior edge of the crest of the spine of the scapula, acromion, posterior border of lateral one-third of clavicle	Motor—Accessory nerve (cranial nerve [XI]). Sensory—(proprioception) anterior rami of C3 and C4	Powerful elevator of the scapula; rotates the scapula during abduction of humerus above horizontal; middle fibers retract scapula; lower fibers depress scapula
Deltoid	Inferior edge of the crest of the spine of the scapula, lateral margin of the acromion, anterior border of lateral one-third of clavicle	Deltoid tuberosity of the humerus	Axillary nerve (C5, C6)	Major abductor of arm; clavicular fibers assist in flexing the arm; posterior fibers assist in extending the arm
Levator scapulae	Transverse processes of C1 and CII vertebrae and posterior tubercles of transverse processes of CIII and CIV vertebrae	Posterior surface of medial border of scapula from superior angle to root of spine of the scapula	Branches directly from anterior rami of C3 and C4 spinal nerves and by branches (C5) from the dorsal scapular nerve	Elevates the scapula
Rhomboid minor	Lower end of ligamentum nuchae and spinous processes of CVII and TI vertebrae	Posterior surface of medial border of scapula at the root of the spine of the scapula	Dorsal scapular nerve (C5)	Elevates and retracts the scapula
Rhomboid major	Spinous processes of TII–TV vertebrae and intervening supraspinous ligaments	Posterior surface of medial border of scapula from the root of the spine of the scapula to the inferior angle	Dorsal scapular nerve (C4, C5)	Elevates and retracts the scapula

322 322 323 323 Both the tr [... Output truncated due to length. 4280 tokens/14654 characters removed ...]