PREVERTEBRAL REGION 



267 



cranium, at the lower border of the pons, with its fellow of 

 the opposite side to form the basilar artery. On account of 

 its varying relations it is divided into four parts. The^rc/ 

 part, which extends from the subclavian artery to the trans- 

 verse process of the sixth cervical vertebra, has been seen 

 already (p. 154). It lies between the longus colli medially, 

 the scalenus anterior laterally, the transverse process of the 

 seventh cervical vertebra and the inferior cervical ganglion of 



Posterior atlanto- 



occipital membrane' 



Posterior ramus of 



sub-occipital nerve 



Greater occipital nerve 



Vertebral artery 



Anterior ramus of a 

 spinal nerve 



Posterior arch of atlas 



v : '-^/-Ligamentum nuchae 



Posterior rami of spinal 

 nerves 



Seventh cervical verteora 



FIG. 100. Dissection of the Ligamentum Nuchas and of the Vertebral 

 . Artery in the Neck. 



the sympathetic posteriorly, and the vertebral vein and the 

 common carotid artery anteriorly (Figs. 53, 54). 



The second part, now exposed, commences where the 

 artery enters the transverse process of the sixth cervical 

 vertebra. It passes vertically upwards, through the series 

 of foramina transversaria, till it reaches the foramen in the 

 transverse process of the epistropheus. In that it runs 

 laterally, as well as upwards, to gain the foramen in the 

 more laterally placed transverse process of the atlas ; and, as 

 it emerges upon the upper aspect of the atlas (Figs. 56, TOO), 

 the third part commences and curves round the lateral and 



