THE ARTERIES. 291 
a. A. vertebralis (Fig. 118, g’).—The vertebral artery 
‘arises from the dorsal surface of the subclavian opposite the 
first rib. It passes craniad and dorsad at the side of the 
thoracic portion of the longus colli muscle, and enters the 
foramen transversarium of the sixth cervical vertebra. It 
passes thence craniad through the foramina transversaria (which 
together form the vertebrarterial canal) and gives off at the 
intervertebral foramina branches 
to the muscles of the neck and 
branches which pass across the 
ventral surface of the spinal 
cord to join A. spinalis anterior. 
Craniad of the foramen transver- 
sarium of the atlas the vertebral 
artery turns dorsad in the groove 
on the lateral surface of the atlas. 
Here it gives off a large branch 
which passes laterodorsad to the 
muscles of the neck and may 
anastomose with a branch of the 
occipital artery. The vertebral 
artery then passes into the verte- 
bral canal through the atlantal 
foramen. It passes to the ventral F!G. 121,—ARTERIES OF THE VEN- 
TRAL SURFACE OF THE BRAIN. 
side of the spinal cord and unites, 4. vertebralis; 4, A. spinalis an- 
at about the level of the foramen tetior; ¢, A. basilaris; ¢, A. cerebelli 
. inferior posterior; e, A. cerebelli an- 
magnum with the vertebral artery terior; 7 A. cerebri posterior; g, cut 
of the opposite side (Fig. 121, a) guisofths twointemel ceotid eters 
to form the basilar artery (A. rotid plexus (g and / are placed within 
pasilaris) (Fig. 121, ¢), which i, ces, steroms or, cele 
passes craniad along the ventral cerebri anterior. 
middle line of the brain. Just before their union the two verte- 
bral arteries (2) give off each a branch which passes caudo- 
mediad. These two branches soon unite in the middle line, 
forming the anterior spinal artery (A. spinalis anterior) (4), 
which passes caudad the entire length of the spinal cord, lying 
on its ventral middle line and receiving many communicating 
branches from the vertebral, intercostal, and lumbar arteries. 
