132 A MANUAL OF ANATOMY. 



Nerve Supply. The external branches of the posterior 

 divisions of the cervical nerves. 



Action. To extend the head and neck, if both act ; to 

 flex the head and neck laterally and rotate them to the 

 same side, if one acts. 



Complexus. Fig. 76. 



Origin. The transverse processes of the upper six 

 dorsal and seventh cervical vertebrae, from the articular 

 processes of the lower three or four cervical vertebrae. 



Insertion. Into the surface of the occipital bone between 

 the inner halves of the superior and inferior curved lines. 



The inner third of the complexus is also called the bi- 

 venter cervicis, inasmuch as its muscular portions are 

 separated by a median tendon. 



Nerve Supply. The upper three or four cervical nerves, 

 through their posterior divisions. 



Action. To extend the head when both act. If one acts 

 it flexes the head laterally. 



DISSECTION. 



Divide the complexus and the trachelomastoid at their cranial attachments, 

 and the levator anguli scapulae at its spinal attachments. The rhomboids and 

 the serratus posticus superior should have been removed by this time by the 

 one dissecting the upper extremity. Carefully remove the dense fascia which 

 covers the muscles forming the suboccipital triangle and fills in the space 

 between them. In dissecting off the fascia covering the suboccipital triangle 

 and the deep muscles of the neck, save the princeps cervicis and the profunda 

 cervicis arteries, and recognize their anastomosis with each other and with the 

 vertebral artery through the triangle. Look for the suboccipital nerve and 

 vertebral artery within the triangle. 



The Suboccipital Triangle. Fig. 19. 



This triangle is formed by the superior oblique externally, 

 the inferior oblique below, and the rectus capitis posticus 

 major internally. 



