288 THE MUSCLES 



MUSCLES OF THE UPPER EXTREMITY 



The first group consists of those which, arising from various parts of the head, 

 neck, and trunk, are inserted into the bones of the shoulder girdle, viz. the clavicle 

 and scapula, or into the humerus. Of this group there are two divisions: the one 

 comprising the nuiscles which take their origin from the back of the head, neck, 

 and trunk; the other, those which arise from the front and sides of the thorax. 



POSTERIOR DIVISION OF THE GROUP OF MUSCLES PASSING 

 FROM THE TRUNK TO THE UPPER EXTREMITY 



This division consists of two layers, which lie superficial to the proper back 

 muscles. Overlying these layers is, first, the superficial fascia, which is strong, 

 well provided with fat, and continuous with that of the head, neck, axilla, 

 and other adjacent regions; and, secondly, the deep fascia, which is thin and 

 forms the sheath of the trapezius and latissimus dorsi muscles. Above and in 

 front, the deep fascia is continuous with the deep cervical fascia; lower down, with 

 the axillary fascia, and that covering the thoracic and abdominal parietes. Inter- 

 nally it is attached to the spines of the vertebrae, and below it blends with the 

 lumbar aponeurosis. 



First Layer 

 Consisting of one muscle — the trapezius. 



THE TRAPEZIUS 



Tlie trapezius (or cucullaris, as it has been called from its resemblance to a 

 cowl = cKCullus) is named from Tpd7:e!^a, a table, on account of the four-sided 

 figure formed by the muscles of the two sides. It is a fan-shaped sheet forming an 

 obtuse-angled triangle, the long side of which corresponds with the spine. 



Origin. — (1) The inner third of the superior nuchal line of the occipital bone, 

 and the external occipital protuberance; (2) the posterior border of the ligamentum 

 nuch^e; (o) the spines of the seventh cervical and all the thoracic vertebrie, together 

 with the supraspinous ligament. 



Insertion. — CI) The posterior border of the outer third of the clavicle and the 

 adjacent part of its upper surface; (2) the inner edge of the upper surface of the 

 acromion process; (3) the upper border of the spine of the scapula, and a small 

 tubercle at its inner extremity. 



Structure. — The origin of the muscle is by short tendinous intermingled with 

 fleshy iibres, except at two places, w'here the tendinous fibres form a continuous 

 sheet. The first of these is from the middle of the ligamentum nucha? to the second 

 thoracic spine; here a conspicuous oval aponeurosis is formed by the tendons of the 

 two sides. The second is at the lower acute angle of the muscle where it arises 

 from the lowest thoracic vertebra. The muscular fibres converge from the extensive 

 origin, and just before their insertion, the sheet of the muscle is folded upon itself, 

 to adapt it to the V-shaped process of the shoulder girdle, into which it is inserted 

 by fleshy fibres, except at the inner extremity of the spine of the scapula, where a 

 tendinous sheet plays over the triangular base of that process, before it is inserted 

 into the tubercle at the inner end of the spine. Sometimes a bursa intervenes 

 between this sheet and the triangular surface of the scapular si)ine. 



Nerve-supply. — From the spinal accessory; and from the deep cervical plexus 

 by branches of tlie third and fourth cervical nerves, which, after communicating 



