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 nuchae, and from the 

 spinous processes of the last cervical and of all the dorsal vertebrae ; 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 verj^ 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, &c. 



The second layer of muscles consists of the rhomboid, levator anguli 

 scapulae, serratus inferior and superior, and the splenii. 



Rhomhoideus 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 nuchae, 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 scapuke 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 vertebrae, 

 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 nuchae 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 inferior, 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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