154 HEAD AND NECK 



the third part of the subclavian artery. In some cases it is the descend- 

 ing branch of the transverse cervical, which then arises directly from the 

 subclavian. In other cases it is the transverse scapular artery. 



Arteria Vertebralis. The vertebral artery is the first 

 branch of the subclavian. It springs from the upper and 

 posterior aspect of the trunk, about 6.2 mm. (a quarter of an 

 inch) from the medial margin of the scalenus anterior, on the 

 right side, and from the point where the vessel reaches the 

 root of the neck, on the left side. Only a small portion of it 

 is seen in the present dissection. It proceeds upwards, in the 

 interval between the longus colli and the scalenus anterior 

 muscles, posterior to the common carotid, and disappears into 

 the foramen transversarium of the sixth cervical vertebra. It 

 is placed very deeply, and is covered anteriorly by its com- 

 panion vein and the common carotid artery. Numerous large 

 sympathetic twigs accompany it. 



The vertebral artery on the left side is posterior to the 

 internal jugular vein and the common carotid artery, and it 

 is crossed by the thoracic duct. 



The vertebral vein issues from the aperture in the transverse 

 process of the sixth cervical vertebra. It passes downwards, 

 antero-lateral to its companion artery, and posterior to the 

 internal jugular vein, to open into the posterior aspect of the 

 commencement of the corresponding innominate vein. Near 

 its termination it crosses the subclavian artery. It receives 

 the deep cervical and the anterior vertebral veins. 



Truncus Thyreocervicalis (O.T. Thyroid Axis). The 

 thyreo-cervical trunk is a short wide vessel, which arises from 

 the anterior aspect of the subclavian artery, close to the 

 medial margin of the scalenus anterior, and under cover of 

 the internal jugular vein. It lies between the phrenic and 

 vagus nerves, and almost immediately breaks up into its 

 three terminal branches viz., the inferior thyreoid, the trans- 

 verse scapular, and the transverse cervical. 



Arteria Thyreoidea Inferior. The inferior thyreoid artery 

 takes a sinuous course to reach the thyreoid gland. First, it 

 ascends for a short distance along the medial border of the 

 scalenus anterior, and under cover of the internal jugular 

 vein ; then, at the level of the cricoid cartilage, it turns 

 suddenly medial wards and passes posterior to the vagus, the 

 sympathetic, and the common carotid artery, to reach the 

 posterior border of the thyreoid gland. There it gives off 



