420 



THE SUBCLAVIAN ARTERIES. 



At its commencement the vertebral artery lies behind the internal jugular, as 

 well as its own companion vein, and on approaching the vertebrae it passes between 

 the longus colli and the scalenus anticus muscles. On the left side, the thoracic 

 duct crosses in front of the artery from within outwards. 



While within the foramina of the cervical vertebrae, the artery is accompanied by 

 a fine plexus of the sympathetic nerve and surrounded by the plexiform vertebral 

 vein : the cervical nerves as they emerge from the intervertebral foramina pass 

 behind it. In the groove of the atlas the artery is at first covered by the superior 



Fig. 351. DEEP DISSECTION OP THE 



NECK, SHOWING THE ORIGIN AND 

 COURSE OP THE VERTEBRAL AR- 

 TERY. (Tiedemann. ) 3 



a, tipper part of sterno-mastoid 

 muscle ; its clavicular part is divided 

 below ; b, spinous process of axis ; c, 

 superior oblique muscle ; d, on the 

 inferior oblique muscle, points by a 

 line to the posterior arch of the atlas ; 

 e, semispinalis colli ; /, placed on the 

 longus colli, points to the transverse 

 process of the sixth cervical vertebra ; 

 g, on the first rib, points to the sca- 

 lenus anticus muscle, cut near its 

 attachment ; 1, innominate artery ; 

 2, right common carotid ; 3, right 

 subclavian ; below it, the origin of 

 the internal mammary artery ; above 

 it, 4, the thyroid axis ; 5, 5, verte- 

 bral artery, passing up through the 

 transverse processes and giving 

 branches to the muscles ; 5', on the 

 vectus posticus major, points to its 

 horizontal part on the arch of the 

 atlas ; 6, deep cervical artery, arising 

 in common with 6', the .superior in- 

 tercostal ; 7, occipital artery, emerg- 

 ing from beneath the sterno-mastoid. 



oblique muscle, and then ap- 

 pears in the suboccipital tri- 

 angle : the suboccipital nerve 

 here lies between the artery 

 and the bone. 



As it enters the subarachnoid space, the artery is crossed by the first tooth of the 

 ligamentum denticulatum (fig. 182, p. 156) ; and then, passing forwards between the 

 origin of the hypoglossal and the anterior root of the suboccipital nerves, it ascends 

 between the anterior surface of the medulla oblongata and the basilar process of the 

 occipital bone. 



The vertebral artery lies loosely in the large foramen of the transverse process of the 

 atlas, and this, together with the bend which it forms between the axis and atlas (fig. 351), 

 allows of the rotation of the latter bone without undue stretching of the vessel. In extreme 

 movements, however, the artery is somewhat compressed on the side from which the head is 

 turned, while on the side towards which the movement is taking place the pressure is 

 diminished (L. Gerlach, in " Beitrage zur Morphologic," &c., Stuttgart, 1884). 



Branches. A. In the neck. (a) Lateral spinal branches. These are several 

 small offsets which pass through the intervertebral foramina into the spinal canal, 

 and there divide, each into two branches ; one of these passes along the roots of the 

 spinal nerve, supplying them and the spinal cord, and anastomoses with the other 



