1452 A MANUAL OF ANATOMY 



bral artery, on leaving the suboccipital triangle, pierces the dura 

 mater and arachnoid, and enters the cranial cavity through the 

 foramen magnum. As it ascends, it lies at first on the side of the 

 medulla oblongata, between the hypoglossal nerve and the anterior 

 root of the suboccipital nerve. It then passes upwards on the 

 ventral surface of the medulla, and, on reaching the lower border 

 of the pons Varolii, it unites with its fellow of the opposite side to 

 form the basilar artery. 



Branches. — These are as follows : posterior meningeal, posterior 

 spinal, posterior inferior cerebellar, anterior spinal, and bulbar. 



The posterior meningeal artery arises from the vertebral artery 

 just before it pierces the dura mater, and it enters the cerebellar 

 fossa of the occipital bone where it supplies the dura mater. 



The posterior spinal artery arises from the vertebral artery 

 immediately after it has pierced the dura mater. It descends 

 upon the side of the spinal cord, in front of the posterior roots of 

 the spinal nerves, and it gives off a branch which descends behind 

 these roots. These two arteries, in themselves small, are reinforced 

 by the spinal branches of the second part of the vertebral artery 

 and of. the dorsal branches of the intercostal arteries. In this 

 manner lateral anastomotic arterial chains are formed upon each 

 side of the spinal cord, in front of, and behind, the posterior nerve- 

 roots. 



The posterior inferior cerebellar artery, of large size, arises a little 

 above the preceding branch. It passes backwards between the 

 pneumogastric and spinal accessory nerves, and then over the 

 restiform body to the vallecula of the cerebellum, where it divides 

 into branches. Some of these supply the inferior verniis, and 

 others ramify on the inferior surface of the cerebellar hemisphere, 

 at the periphery of which they anastomose with branches of the 

 superior cerebellar artery. The artery furnishes branches to the 

 corresponding choroid plexus of the fourth ventricle and to the 

 medulla oblongata. 



The anterior spinal branch of the vertebral artery arises from that 

 vessel near its termination. It passes obliquely downwards and 

 inwards over the ventral aspect of the medulla oblongata, and at 

 the median line it unites with its fellow of the opposite side to form 

 the anterior spinal artery of the spinal cord. It furnishes twigs to 

 the medulla oblongata. 



The bulbar branches are distributed to the medulla oblongata. 



Basilar Artery. — ^This vessel is formed by the union of the two 

 vertebral arteries. It extends from the lower to the upper border 

 of the pons Varolii, occupying the median basilar groove on its 

 ventral surface. It lies beneath the arachnoid membrane, within 

 the cisterna fontis, and at the upper border of the pons it divides 

 into the two posterior cerebral arteries. 



Branches. — ^These are as follows, on either side : transverse, 

 internal auditory, anterior inferior cerebellar, superior cerebellar, 

 and posterior cerebral. 



