624 THE VASCULAR SYSTEMS 



superior cerebellar branches of the basilar artery. Branches from this artery 

 supply the choroid plexus of the fourth ventricle. 



The bulbar arteries comprise several minute vessels which spring from the 

 vertebral and its branches and are distributed to the medulla oblongata. 



The basilar artery (a. basilaris) (Fig. 449), so named from its position at the base 

 of the skull, is a single trunk formed by the junction of the two vertebral arteries; 

 it extends from the posterior to the anterior border of the pons, lying in the median 

 pontile groove, under cover of the arachnoid. It ends by dividing into the two 

 posterior cerebral arteries. 



Branches. Its branches on either side are the following: 



Transverse. Anterior inferior cerebellar. 



Internal auditory. Superior cerebellar. 



Posterior cerebral. 



The transverse or pontile branches (ram?' ad pontem) are a number of small vessels 

 which come off at right angles on either side of the basilar artery and supply the 

 pons and adjacent parts of the brain. 



The internal auditory (a. auditiva interna), a long slender branch, arises from 

 near the middle of the artery; it accompanies the corresponding auditory nerve 

 into the internal auditory meatus and is distributed to the internal ear. 



The anterior inferior cerebellar artery (a. medicerebellaris, a. cerebelli inferior 

 anterior) passes backward, to be distributed to the anterior part of the under sur- 

 face of the cerebellum, anastomosing with the posterior inferior cerebellar branch 

 of the vertebral. 



The superior cerebellar artery (a. praecerebellaris, a. cerebelli superior) arises 

 near the termination of the basilar. It passes outward, immediately behind 

 the oculomotor nerve, which separates it from the posterior cerebral artery, winds 

 around the crus, close to the trochlear nerve, and, arriving at the upper surface of 

 the cerebellum, divides into branches which ramify in the pia and, reaching the 

 circumference of the cerebellum, anastomose with the branches of the inferior 

 cerebellar artery. Several branches are given to the epiphysis, the valve of Vieus- 

 sens, and the velum interpositum. 



The posterior cerebral artery (a. postcerebralis, a. cerebri posterior) (Figs. 449 

 and 454) is larger than the preceding, from which it is separated near its origin by 

 the oculomotor nerve. Passing outward, parallel to the superior cerebellar artery, 

 and receiving the posterior communicating from the internal carotid, it winds 

 around the crus, and passes to the under surface of the temporal lobe of the cere- 

 brum, and divides up into branches for the supply of the temporal and occipital 

 lobes. 



The branches of the posterior cerebral artery are: 



( Postero-median ganglionic. ( Anterior temporal. 



Ganglionic < Posterior choroid. Cortical < Posterior temporal. 



( Postero-lateral ganglionic. ( Occipital. 



Ganglionic. The postero-median ganglionic branches (Fig. 454) are a group of 

 small arteries which arise at the commencement of the posterior cerebral artery; 

 these, with similar branches from the posterior communicating, pierce the posterior 

 perforated substance, and supply the internal surfaces of the thalamus and the 

 walls of the third ventricle. The posterior choroid enters the interior of the brain 

 beneath the splenium of the corpus callosum, and supplies the velum interpositum 

 and the choroid plexus. The postero-lateral ganglionic branches are a group of 

 small arteries which arise from the posterior cerebral artery, after it has turned 

 around the crus; they supply a considerable portion of the thalamus. 



