THE VERTEBRAL ARTERY. 



759 



{d) The posterior spinal artery (a spinalis posterior) is a slender vessel which anasto- 

 moses below with the posterior ascending' ramus of the uppermost spinal branch from the 

 cervical portion of the vertebral and forms the uppermost part of the posterior spinal artery. 



[e) The anterior spinal artery (a. spinalis anterior), much larger than the preceding, arises 

 from the inner surface of the vertebral, a short distance before the latter unites with its fellow 

 to form the basilar. It passes downward and towards the ventral median line, and unites with 

 its fellow to form a single median longitudinal stem which extends the entire length of the 

 spinal cord along the hne of the anterior median fissure, receiving reinforcing branches from 

 the various spinal branches of tlie \ertebral, intercostal, lumbar, and lateral sacral arteries. 



{/) The posterior inferior cerebellar artery (a. cerebelli inferior posterior) arises at about the 

 same level as the preceding vessel, but from the outer surface of the vertebral. It passes 

 upward over the sides of the medulla oblongata to supply the lower surface of the cerebellum, 



Fig. 702. 



Anterior cerebral artery 



Olfactory tract, cut 



Anterior cerebral 



artery 



Internal carotid artery 



Pituitary body 

 Anterior choroid 

 artery 

 Posterior communi- 

 cating artery 



Corpora mammillaria 

 Posterior cerebral 



artery 

 Superior cerebellar 



artery 



A pontine artery . 

 Auditory artery 



Trigeminal nerve 



Vertebral artery 



Right lobe of 

 cerebellum 



Anterior communicating 

 artery 



Optic chiasm 



Internal carotid artery 

 Middle cerebral artery 



Antero-lateral gang- , 

 lionic arteries 

 Posterior com. arteries 

 Anterior choroid artery 

 Oculomotor nerve 

 Posterior cerebral artery 

 Sup. cerebellar artery 



Basilar artery 



Pons 



Anterior inferior cerebel- 

 lar artery 



Anterior spinal artery 

 Medulla oblongata 



Posterior inferior cere- 

 bellar artery 



Vertebral artery 



Inferior surface of brain, showing internal carotid, vertebral and basilar arteries and circle of 

 Willis; apex of left temporal lobe has been removed to expose ganglionic arteries. 



giving branches to the medulla and to the choroid plexus of the fourth ventricle and anasto- 

 mosing with the superior cerebellar artery. 



From the basilar artery, (Fig. 702) the anterior median continuation of the vertebrals. 



(^) Numerous transverse arteries are given of? and pass outward over the pons to supply 

 that structure and the adjacent portions of the brain. 



{h) The internal auditory arteries (aa. audiiivae internae), one on each side, are additionally 

 given of?, and accompany. the auditory nerve through the internal auditory meatus to supply the 

 internal ear. 



{i) The anterior inferior cerebellar arteries (aa. cerebelli inferiores anteriores), pass out- 

 ward on either side over the surface of the pons to the lower surface of the anterior portion of the 

 cerebellum, supplying that structure and anastomosing with the superior cerebellar arteries. 



(7) The superior cerebellar arteries (aa. cerebelli superiores). These arise from the basilar, 

 immediately behind its division into the posterior cerebral arteries. They pass outward and 

 backward over the pons and the crura cerebri, immediately behind the roots of the oculo-motor 



