VERTEBRAL ARTERY. 773 
b) Cortical branches are given off as the middle cerebral artery passes over the surface 
of the island of Reil at the bottom of tbe Sylvian fissure, as follows :— 
(6) The inferior external orbital runs forwards and outwards, and is distributed to 
the outer part of the orbital surface of the frontal lobe and to the inferior frontal con- 
volution. 
(67) The ascending frontal branch turns round the upper margin of the Sylvian 
fissure, and is distributed to the ascending frontal convolution and to the posterior part 
of the middle frontal convolution. 
(6°) The ascending parietal branch emerges from the Sylvian fissure and passes up- 
wards along the posterior border of the ascending parietal convolution, supplying that 
convolution and the superior parietal lobule. 
(6+) The temporal branch passes out of the Sylvian fissure, and turns downwards to 
supply the superior and middle temporal convolutions. 
(6°) The parieto-temporal branch continues backwards, in the direction of the main 
stem, and emerges from the posterior end of the Sylvian fissure ; it supplies the inferior 
parietal lobule, the external occipital convolutions, and the posterior part of the temporo- 
sphenoidal lobe. 
VERTEBRAL ARTERY. 
The vertebral artery (a. vertebralis, Figs. 556 and 559) is the first branch 
given off from the subclavian trunk ; it arises from the upper and back part of the 
parent stem, opposite the interval between the anterior scalene and the longus 
colli muscles, and terminates at the lower border of the pons Varolii by uniting 
with its fellow of the opposite side to form the basilar artery. 
Course and Relations.—The vertebral artery is divisible into four parts. 
The first part runs upwards and backwards, between the scalenus anticus and 
the outer border of the longus colli, to the foramen in the transverse process of the 
sixth cervical vertebra. It is surrounded by a plexus of sympathetic nerve fibres, 
covered anteriorly by the vertebral and internal jugular veins, and crossed in front 
by the inferior thyroid artery. On the left side the terminal part of the thoracic 
duct also passes in front of it. The second part runs upwards through the foramina 
in the transverse processes of the upper six cervical vertebre. As far as the 
second cervical vertebra its course is almost vertical; as it passes through the 
transverse process of the axis, however, it is directed obliquely upwards and 
outwards to the atlas. It is surrounded by a plexus of sympathetic nerve fibres, 
and also by a plexus of veins. The artery les in front of the trunks of the 
cervical nerves, and internal to the intertransverse muscles. The third part emerges 
from the foramen in the transverse process of the atlas, between the anterior primary 
division of the suboccipital nerve internally and the rectus capitis lateralis exter- 
nally, and runs almost horizontally backwards and inwards round the outer side 
and back of the superior articular process of the atlas. In this course it enters 
the suboecipital triangle, where it les in the groove on the upper surface of the 
posterior arch of the atlas (sulcus arterie vertebralis). It is separated from the 
bone by the suboccipital nerve, and is overlapped superficially by the adjacent 
borders of the superior and inferior oblique muscles. Finally, this part of the 
artery passes beneath the oblique hgament of the atlas and enters the spinal canal. 
The fourth part pierces the spinal dura mater and runs upwards into the cranial 
cavity. It passes between the roots of the hypoglossal nerve above and the first 
dentation of the hgamentum denticulatum below, pierces the arachnoid,and, gradually 
inclining inwards in front of the medulla, reaches the lower border of the pons 
Varolii, where it unites with its fellow of the opposite side to form the basilar artery. 
Branches.—J/’rom the first part.—As a rule there are only a few small muscular 
twigs from this portion of the artery. 
From the second part.—(1) Muscular branches which vary in number and size. ‘They 
supply the deep muscles of the neck, and anastomose with the profunda cervicis, the 
ascending cervical, and the occipital arteries. 
(2) Spinal branches (rami spinales) pass from the inner side of the second part of the 
vertebral artery through the intervertebral foramina into the spinal canal, where they 
give off twigs which pass along the roots of the spinal nerves to reinforce the anterior and 
