382 THE BRAIN 



the central system, and the vessels which constitute that 

 group do not anastomose with each other. The cortical 

 vessels supply the cerebral cortex and the finer branches, 

 which ramify in the pia mater, anastomose with one another ; 

 therefore, the neighbouring vascular districts of the cerebral 

 cortex are not sharply cut off from one another. 



Arteriae Vertebrates. Each vertebral artery enters the sub- 

 arachnoid space, in the upper part of the vertebral canal, by 

 piercing the dura mater and the arachnoid. Gaining the 

 interior of the cranium, through the foramen magnum, it 

 runs upwards, at first, on the side of the medulla oblongata, 

 but it soon inclines to the anterior aspect of the medulla 

 oblongata, and, meeting its fellow of the opposite side in 

 the median plane, it unites with it, at the lower border of 

 the pons, to form the basilar artery. 



The branches given off from the intracranial part of the 

 vertebral artery are : 



1. Posterior spinal. 3. Anterior spinal. 



2. Posterior inferior cerebellar. 4. Bulbar. 



Arteria Spinalis Posterior. The posterior spinal artery is 

 the first branch given off from the vertebral artery after it 

 pierces the dura mater. It passes, downwards, on the spinal 

 medulla along the line of the posterior nerve-roots (p. 90). 



Arteria Cerebelli Inferior Posterior. The posterior inferior 

 cerebellar artery is the largest branch of the vertebral artery. 

 It takes origin immediately above the posterior spinal artery, 

 and pursues a tortuous course backwards, on the side of the 

 upper part of the medulla oblongata, between fila of the 

 hypoglossal nerve, and then between fila of the vagus. 

 Finally, turning round the restiform body, it gains the vallecula 

 of the cerebellum and enters the cisterna cerebello-medullaris, 

 where it ends by dividing into two terminal branches. One 

 of the branches ramifies on the posterior part of the inferior 

 surface of the corresponding cerebellar hemisphere, the other 

 runs backwards, in the vallecula, in the groove between the 

 vermis and the hemisphere supplying both. The trunk of 

 the artery gives branches to the medulla oblongata which 

 supply the olive, and the fibres of the spino-cerebellar, the 

 spino-thalamic, the rubro-spinal, and the olivo-cerebellar 

 tracts, as well as the nuclei of the vagus and glosso-pharyngeal 

 nerves (Bury and Stopford). 



Arteria Spinalis Anterior. The anterior spinal artery arises 



