PREVERTEBRAL REGION 355 



laterally, the transverse process of the seventh cervical 

 vertebra and the inferior cervical ganglion of the sympathetic 

 posteriorly, and the vertebral vein and the common carotid 

 artery anteriorly. 



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, the third 

 part commences and curves round the lateral and posterior 

 aspects of the upper articular process of that bone, in a 

 groove upon the upper surface of the posterior arch. As 

 soon as it has passed under cover of the lateral margin of the 

 posterior atlanto-occipital membrane it becomes the fourth 

 part. The fourth part turns upwards, pierces the dura mater 

 and passes into the skull through the foramen magnum, 

 anterior to the uppermost digitation of the ligamentum denti- 

 culatum ; then, turning antero-medially, between the hypo- 

 glossal nerve above and the first cervical nerve below, it 

 passes to the anterior surface of the medulla oblongata, and, 

 as already stated, joins its fellow of the opposite side at the 

 lower border of the pons. 



Relations. The relations of the first part have already 

 been sufficiently considered. The second part lies in and 

 between the transverse processes of the cervical vertebrae, 

 medial to the intertransverse muscles, lateral to the bodies 

 of the vertebrae, and anterior to the anterior branches of the 

 cervical nerves as they pass laterally. It is surrounded not 

 only by the sympathetic nerve plexus derived from the 

 inferior cervical ganglion, which accompanies all parts of 

 the artery, but also by a venous plexus which terminates below 

 in the vertebral vein or veins. The third part of the artery 

 lies on the posterior arch of the atlas in the anterior boundary 

 of the sub-occipital triangle. As it turns posteriorly from the 

 foramen in the transverse process of the atlas the anterior 

 branch of the first cervical nerve lies to its medial side, 

 between it and the lateral mass of that bone ; and, as it turns 

 medially, posterior to the upper articular facet, the trunk of 

 the first cervical nerve lies below it on the posterior arch, and 



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