OF THE BACK. 



337 



the mastoid process, and a third incision from its lower end, along the crest of the ilium to 

 about its middle. This large intervening space should, for convenience of dissection, be sub- 

 divided by a fourth incision, extending obliquely from 

 the spinous process of the last dorsal vertebra, upward 

 and outward, to the acromion process. This incision cor- 

 responds with the lower border of the Trapezius muscle. 

 The flaps of integument are then to be removed in the 

 direction shown in the figure. 



The superficial fascia is exposed upon re- 

 moving the skin from the back. It forms a 

 layer of considerable thickness and strength, 

 in which a quantity of granular pinkish fat is 

 contained. It is continuous with the super- 

 ficial fascia in other parts of the body. The 

 deep fascia is a dense fibrous layer attached to 

 the occipital bone, the spines of the vertebrae, 

 the crest of the ilium, and the spine of the 

 scapula. It covers over the superficial muscles, 

 forming sheaths for them, and in the neck 

 forms the posterior part of the deep cervical 

 fascia ; in the thorax it is continuous with the 

 deep fascia of the axilla and chest, and in the 

 abdomen with that covering the abdominal 

 muscles. 



The Trapezius (Fig. 213) is a broad, flat, 

 triangular muscle, placed immediately beneath 

 the skin and fascia, and covering the upper and 

 tack part of the neck and shoulders. It arises 

 from the external occipital protuberance and the 

 inner third of the superior curved line of the 

 occipital bone ; from the ligamentum nuchse, 

 the spinous process of the seventh cervical, and those of all the dorsal vertebrae ; 

 and from the corresponding portion of the supraspinous ligament. From this 

 origin the superior fibres proceed downward and outward, the inferior ones 

 upward and outward, and the middle fibres horizontally, and are inserted, 

 the superior ones into the outer third of the posterior border of the clavicle ; 

 the middle fibres into the inner margin of the acromion process, and into the 

 superior lip of the posterior border or crest of the spine of the scapula; the 

 inferior fibres converge near the scapula, and terminate in a triangular apo- 

 neurosis, which glides over a smooth surface at the inner extremity of the 

 spine, to be inserted into a tubercle at the outer part of this smooth surface. 

 The Trapezius is fleshy in the greater part of its extent, but tendinous at its origin 

 and insertion. At its occipital origin it is connected to the bone by a thin fibrous 

 lamina, firmly adherent to the skin, and wanting the lustrous, shining appearance 

 of aponeuroses. At its origin from the spines of the vertebrae it is connected to 

 the bones by means of a broad semi-elliptical aponeurosis, which occupies the 

 .space between the sixth cervical and the third dorsal vertebrae, and forms, with 

 the aponeurosis of the opposite muscle, a tendinous ellipse. The rest of the muscle 

 arises by numerous short tendinous fibres. If the Trapezius is dissected on both 

 sides, the two muscles resemble a trapezium or diamond-shaped quadrangle ; two 

 angles corresponding to the shoulders ; a third to the occipital protuberance ; 

 and the fourth to the spinous process of the last dorsal vertebra. 



The clavicular insertion of this muscle varies as to the extent of its attach- 

 ment ; it sometimes advances as far as the middle of the clavicle, and may even 

 become blended with the posterior edge of the Sterno-mastoid or overlap it. This 

 should be borne in mind in the operation for tying the third part of the subclavian 

 artery. 



FIG. 212. Dissection of the muscles of 

 the back. 



