138 THE HEAD AND NECK 



and its fibres can be seen extending upwards to the spine of the 

 second cervical vertebra. Along its lateral border the articular 

 processes of the cervical vertebrae can be made out, while the 

 muscular sub-occipital triangle is exposed in the upper part of 

 the incision (Fig. 43). 



The lower boundary of the sub-occipital triangle is formed by the inferior 

 oblique, which extends from the spine of the second cervical vertebra to the 

 transverse process of the atlas. The medial boundary, formed by the rectus 

 capitis posterior major, extends from the spine of the second cervical vertebra 

 upwards to the occipital bone ; and the lateral boundary, formed by the 

 superior oblique, ascends from the transverse process of the atlas to the 

 occipital bone. The floor of the triangle is formed by the posterior arch of 

 the atlas and the posterior atlanto-occipital membrane (ligament). The 

 vertebral artery lies on the lateral part of the floor. After leaving the fora- 

 men in the transverse process of the atlas, it bends round the posterior aspect 

 of the lateral mass prior to piercing the posterior atlanto-occipital membrane 

 and the dura mater. In this part of its course the artery is separated from 

 the posterior arch of the atlas by the posterior ramus (primary division) of 

 the first cervical nerve, which at once breaks up into small branches to 

 supply the surrounding muscles. 



The most important landmark at this stage is the greater 

 occipital nerve. It emerges at the lower border of the inferior 

 oblique and at once turns upwards and medially into the re- 

 tracted flap (Fig. 43). At the lower border of the inferior 

 oblique the greater occipital nerve gives off a communicating 

 branch, which enters the sub-occipital triangle and joins the 

 first cervical nerve. It is essential that this branch should be 

 found and traced, as in this way the first cervical nerve can be 

 found with a minimum of risk to the vertebral artery. The 

 first cervical and the greater occipital nerves the latter repre- 

 sents the posterior ramus (primary division) of C. 2 are cut away 

 as close to their origins as possible. 



The lower nerves are embedded in the fascia which separates 

 the semispinalis capitis (complexus) from the semispinalis 

 cervicis. If this fascia is left behind when the former muscle 

 is undermined, the nerves will be found on the surface of the 

 latter (Fig. 43) ; if not, they will be found on the deep surface 

 of the semispinalis capitis. They should be traced to the 

 lateral border of the semispinalis capitis and there cut away, 

 close to the articular processes. 



The Deep Triangle of the Neck is a well-defined region 

 which is of great importance to the surgeon, more especially 

 on the left side. It lies behind the lower part of the carotid 

 sheath and is bounded medially by the longus colli and laterally 

 by the scalenus anterior. The two muscles converge above 



