THE BACK. 93 



wrinkles the skin of the neck and depresses the lower 

 jaw. In the cow and horse it is so highly developed 

 that by it the skin can be contracted all over the body to 

 drive off flies. The rectus capitis anticus major arises 

 from the third to the sixth cervical vertebrae and is in- 

 serted into the occipital bone, serving to flex the head. 

 The scalenus muscles have their origin on the lower cer- 

 vical vertebrae and are inserted into the first and second 

 ribs, thus aiding in the elevation of the ribs as well as in 

 lateral flexion of the neck. The head is held upright by 

 the ligamentum nuchce, which rises from the external 

 occipital protuberance and is inserted into the spinous 

 processes of all the cervical vertebrae except the first. 



Muscles of the Back. The chief back muscles are the 

 trapezius and the latissimus dorsi, which together cover 

 in the back pretty thoroughly. The trapezius arises 

 from the occipital bone, the ligamentum nuchae, and the 

 spinous processes of the seventh cervical and all the 

 dorsal vertebrae and is inserted into the outer third of the 

 clavicle or collar bone and the acromion process and spine 

 of the scapula or shoulder blade. It is thus triangular in 

 shape and covers in the neck and shoulders, serving to 

 draw the head back and to the side. It overlaps the 

 latissimus dorsi. 



The latissimus dorsi has its origin by aponeurosis from 

 the spinous processes of the six lower dorsal and all the 

 lumbar and sacral vertebrae, from the crest of the ilium or 

 hip bone, and from the three or four lower ribs, swings 

 across the side, dwindling in size, and is inserted by a 

 small tendon into the bicipital groove of the humerus or 

 upper arm bone, thus covering in the part of the back 

 not covered by the trapezius. It draws the arm down 

 and back, raises the lower ribs, and draws the trunk for- 

 ward, as in climbing. The flat muscles of the back and 

 abdomen have a tendency to flatten out into aponeuroses, 

 such as occurs in the origin of the latissimus dorsi. 



The levator scapulas, from the transverse processes of 

 the upper cervical vertebrae to the posterior border of the 



