BASILAR 511 



Branches of the Third or Occipital Portion 



1. Muscular, to the muscles forming the suboccipital triangle; 2. anasto- 

 motic, U) the branches of the occipital artery. 



Branches of the Fourth or Cranial Portion 



1. The posterior meningeal is a small bnuich given oft" as the vertebral artery 

 pierces tlie dura mater to enter the cranium. It sui)plies the bone and dura mater 

 of the posterior fossa of the skull, and anastomoses with the jjosterior meningi'al 

 branches derived from the occipital and ascending pharyngeal arteries. It gives 

 branches to the falx cerel»elli (lig. 387). 



2. The posterior spinal artery runs downwards oljliquely along the side of the 

 medulla to the back of the cord, dcnvn wliich it passes behind the roots of the 

 spinal nerves, l)eing reinforced by lateral branches running iiiAvards along these 

 nerves, in the neck from the vertebral, in the dorsal region from the intercostals, 

 and in the lumbar region from the lumbar arteries. It can be traced as Ioav as the 

 end of the spinal cord. 



3. The anterior spinal artery comes off from the vertebral a little ])elow its 

 termination in the basilar artery. Descending ol)liquely inwards in front of the 

 medulla, it unites on a level with the foramen magnum with its fellow of the op- 

 posite side. The single vessel thus formed runs downwards in fi'ont of the spinal 

 cord beneath the pia mater as far as the termination of the cord, being reinf<irccd 

 by the lateral spinal l)ranches the whole way down (fig. 387). The spinal arteries 

 are descril^ed in detail with the anatomy of the spinal cord. 



4. The posterior inferior cerebellar (fig. 340) — the largest branch of the 

 vertebral — arises from that vessel just before it joins its fellow to form the basilar 

 artery. At times it may come off from the basilar itself. It runs, at first outwards 

 across the restiform body between the origin of the pneumogastric and hypoglossal 

 iierves, and, descending towards the vallecula, there divides intc) two ])ranches, an 

 internal and external, (a) The internal or inferior vermiform branch runs 

 backwards Ijetween the vermiform i)rocess and the lateral hcniisi»hcrc of the cere- 

 belkim. It supplies the vermiform process, and anastomoses Avith the artery of 

 the o]:)posite side, and with tlie su])erior vermifoiin Ijranch of the superior cere- 

 bellar, {b) The external or hemispheral branch runs outwards, and, ramifying 

 over the under surface of the cereV)cllar hemisphere, supplies its cortex and anas- 

 tomoses along its outer margin with the superior cerebellar arteries. 



From the undivided trunk of the posterior inferior cerebellar artery branches are 

 given to the choroidal plexus and the fourth ventricle. 



THE BASILAR ARTERY 



The basilar artery is formed by the confluence of the right and left vertel)ral 

 arteries, which meet at an acute angle at the lower liorder of the pons Varolii. It 

 runs forwards and upwards in a slight groove in the middle line of the pons, and 

 divides at the upper l)order of that structure at the level of the i)retentorial oj>ening 

 into the two posterior cerebral arteries. 



Branches of the Basilar Artery 



The branches of the basilar artery are: — 1. Transverse or pontal; 2. internal 

 auditory; 3. anterior cerebellar: 4. stqierior cerel)ellar; 5. ])osterior cerel)ral. 



1. The transverse or pontal arteries are numerous small vessels which come 

 off at right angles on either side of the basilar artery, and, passing outwards over 

 the ])ons. supply that structure and adjacent parts of the brain. 



2. The internal auditory artery, a long slender vessel, accompanies tlie audi- 

 tory nerve into the internal auditory meatus (fig. 387). It here lies Itetween the 

 facial and auditory nerves, and at the l)ottom of the meatus passes into the internal 

 ear, and anastomoses with the other auditory arteries. (See Internal Ear.) 



