THE HEAD AND NECK 



1065 



extremity of the transverse process of the atlas at its back 

 part. 



Insertion. — ^The occipital bone between the outer parts of the 

 superior and inferior curved lines. 



Nerve-supply. — ^The posterior primary division of the suboccipital 

 nerve. 



The direction of the fibres is upwards and inwards. 



Action. — (i) To extend the head ; and (2) to act as a slight lateral 

 flexor of the head. 

 * The muscle is triangular. 



Suboccipital Triangle. — ^This triangle is situated under cover of 

 the upper part of the complexus, close below the occipital bone. 



Recti Capitis Postici Minores 



A 



Rectus Capitis Posticus 



Major 



Posterior Tubercle of Atlas 



Spinous Process of Axis 



Interspinales^-v;."' 



.Suboccipital Triangle 



Obliquus Capitis 

 Superior 



-Mastoid Process 



~ Vertebral Artery 



- — ,_ (Third Part) 



■-■^^ ~" — Posterior Division of 

 ^^^^ Suboccipital Nerve 

 "^ Transverse Process of 

 -,^ Atlas 



'■"•^^Obliquus Capitis Inferior 

 Great Occipital Nerve 



___J'.raSemispinalis Colli (upper 

 " two bundles) 



Fig. 436. — The Suboccipital Triangle. 



Boundaries — Sup era-internal. — ^The rectus capitis posticus major. 

 Super 0- external. — ^The obliquus capitis superior. Inferior. — ^The 

 obliquus capitis inferior. The roof is formed by the complexus, 

 and the floor by half of the posterior arch of the atlas, and half 

 of the posterior occipito-atlantal ligament. The contents are 

 (i) the third part of the vertebral artery, (2) the suboccipital plexus 

 of veins, and (3) the posterior primary division of the suboccipital 

 nerve. 



Third Part of the Vertebral Artery. — The vertebral artery, having 

 emerged from the costo-transverse foramen of the atlas, enters 

 upon the third part of its course, and takes a winding course back- 

 wards and inwards. It lies in the vertebrarterial groove of the 

 atlas, the posterior primary division of the suboccipital nerve 

 being beneath it, and it passes under an arched band of the 



