THE MUSCLES OF THE SHOULDER GIRDLE 251 



(b) Trapezius thoracalis s. dorsalis. — Origin. — The supraspinous ligament, 

 from the third to the tenth thoracic vertebra. 



Insertion. — The tubercle of the spine of the sca]>ula. 



Action. — Acting as a whole, to elevate the shoulder; the cervical portion 

 draws the scapula forward and upward and the thoracic portion draws it backward 

 and upward. 



Structure. — The muscle arises by a short, thin aponeurosis, from which the 

 fibers of the flat fleshy portion converge to the spine of the scapula and the apo- 

 neurosis which separatees the two portions. The cervical fascia joins the ventral 

 edge of the cervical portion to the mastoido-humeralis, or the two muscles may 

 unite here. 



Relations. — Superficially, the skin and fascia; deeply, the rhomboideus, 

 latissimus dorsi, supraspinatus, infraspinatus, deltoid, splenius, serratus magnus, 

 and anterior deep pectoral muscles, and the cartilage of the scapula. 



Blood-supply. — Deep cervical and intercostal arteries. 



Nerve-supply. — Spinal accessory nerve. 



Second Layer 



This consists of two muscles — the rhomboideus and the latissimus dorsi. 



2. Rhomboideus. — This consists of two portions: 



(a) Rhomboideus cervicalis s. cervicis. — Origin. — The funicular portion of 

 the ligamentuni nuchie, from the second cervical to the second thoracic vertebra. 



Insertion. — The internal surface oi the cartilage of the scapula. 



(b) Rhomboideus thoracaUs s. dorsalis. — Origin. — The spinous processes 

 of the second to the seventh thoracic verteljra by means of the dorso-scapular 

 ligament. 



Insertion. — -The inner surface of the cartilage of the scapula. 



Action. — -To draw the scapula upward and forward. When the limb is 

 fixed the cervical portion will elevate the neck. 



Structure. — The cervical portion is narrow, pointed at its anterior extremity, 

 and lies along the funicular part of the ligamentum nuchae, to which it is attached 

 by short tendon bundles. The fibers are directed for the most part longitudinally. 

 The thoracic portion is quadrilateral in shape, and its fibers are nearly vertical. 

 Its deep face is intimately attached to the dorso-scapular ligament. 



Relations. — Superficially, the skin and fascia (over a small area), the trape- 

 zius, and the cartilage of the scapula; deeply, the dorso-scapular ligament, the 

 splenius, complexus, longissimus dorsi, and serratus anticus. 



Blood-supply. — Dorsal and superior cervical arteries. 



Nervc-supph/. — Sixth cervical nerve. 



3. Latissimus Dorsi. — This is a wide muscle which has the form of a right- 

 angled triangle. It lies for the most part under the skin and panniculus, on the 

 lateral wall of the thorax, from the spine to the arm. 



Origin. — The lumbo-dorsal fascia — and by this means from the lumbar and 

 thoracic spines as far forward as the highest point of the withers. 



Insertion. — The internal tubercle of the humerus, in common with the teres 

 major. 



Action. — To draw the humerus upward and backward and flex the shoulder- 

 joint. If the limb is advanced and fixed, it draws the trunk forward. 



Structure. — The muscle arises by a wide aponeurosis, which fuses with that 

 of the serratus posticus and with the lumbo-dorsal fascia. The muscular portion 

 is at first rather thin, but by the convergence of its fibers becomes thicker as it 

 approaches the arm. The anterior fibers pass almost vertically downward over 

 the dorsal angle of the scapula and its cartilage. The posterior fibers are directed 



