MYOLOGY. 57 
D. Muscles of the Back. 
The muscles of the back are many of them indistinct, and vary con- 
siderably in different bodies. They are symmetrical on each side, and may 
be arranged in four successive layers, each nearly covering the other, 
between the integuments and the bones. The muscles of the first layer are 
two in number. 
The trapezius, broad and triangular, with the base along the spine, the 
apex at the shoulder, arises from the internal third of the superior transverse 
ridge of the occipital bone, from the ligamentum nuche, and from the 
spinous processes of the last cervical and of all the dorsal vertebre ; it is 
inserted into the posterior border of the external third of the clavicle and 
of the acromion process of the scapula. Its use is to raise and draw back- 
wards the shoulder. 
The latissimus dorsi is triangular and very broad, covering the greater 
part of the lumbar and dorsal region ; it arises from all the lumbar spines 
and supra-spinal ligaments, also from the pelvis and last three or four 
ribs; its insertion is into the concave surface and into the inner or 
posterior edge of the bicipital groove. Use: to depress the shoulder and 
arm, to draw the arm backwards and inwards, to rotate the humerus 
inwards, Xc. 
The second layer of muscles consists of the rhomboid, levator anguli 
scapule, serratus inferior and superior, and the splenii. 
Rhomboideus is broad and thin, and is the most superficial of this layer ; 
it is divided into a superior or minor portion, and an inferior or major; the 
former arises from the lower part of the ligamentum nuchee, and from the 
two last cervical spinous processes, and is inserted into the base of the 
scapula, opposite to and above the spine; the major portion arises from the 
four or five superior dorsal spines, and is inserted into a thin tendinous arch, 
extending along the base of the scapula from its spine to its inferior angle. 
Use: to draw the shoulder backwards and upwards. 
Levator anguli scapule is a long and flat muscle, placed at the upper and 
posterior part of the side of the neck; it arises from the posterior tubercles 
of the transverse processes of the four or five superior cervical vertebre, 
and is inserted into the base of the scapula, between the spine and the supe- 
rior angle; its use is to elevate the whole scapula, when it is assisted by the 
trapezius, or alone, to raise the superior angle. 
Serratus posticus superior is placed on the superior posterior part of the 
thorax, arises from the ligamentum nuche and from two or three dorsal 
spines, and forms a thin fleshy belly ending in three fleshy strips, which are 
inserted into the upper borders of the second, third, and fourth ribs, external 
to their angles. Use: to expand the thorax by elevating the ribs, and 
drawing them outwards. 
Serratus posticus enferior, at the lower part of the dorsal and upper part 
of the lumbar regions, arises by a tendinous expansion, connected through 
the lumbar fascia to the two last dorsal and two upper lumbar spines. — Its 
three or four fasciculi are inserted into the lower edges of the four inferior 
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