THE CIRCULATION OF THE RHOMBENCEPHALON. 2Q 



The anterior inferior cerebellar artery (a. cerebelli anterior 

 inferior, Fig. 9) is given off by the basilar near the junction of 

 its inferior and middle thirds. (Sometimes it is replaced by 

 two or three small vessels.) It runs lateralward, behind the 

 flocculus, keeping close to the anterior border of the hemisphere. 

 In its course it passes anterior to the abducent nerve and posterior 

 to the facial and auditory nerves. It supplies the anterior part 

 of the under surface and border of the cerebellar hemisphere. 



The posterior inferior cerebellar artery (a. cerebelli inferior 

 posterior, Fig. 9) is the largest branch of the vertebral and is given 

 off just before the vertebral arteries unite and form the basilar. 

 Passing first between the root-bundles of the hypoglossal nerve 

 and then between those of the accessory and vagus nerves, the 

 posterior inferior cerebellar artery bends at a right angle back- 

 ward and runs between the medulla and the cerebellar hemisphere, 

 where it divides into a medial and a lateral branch. The medial 

 branch follows the sulcus valleculae and gives branches to the 

 medial part of the hemisphere and the vermis inferior. It anas- 

 tomoses with its fellow of the opposite side. The lateral branch, 

 runs lateralward from the posterior cerebellar notch over the 

 inferior surface of the hemisphere; its terminal branches wind 

 around the postero-lateral border and communicate with the 

 superior cerebellar artery on the upper surface of the hemisphere. 

 The undivided trunk of the posterior inferior cerebellar artery 

 gives small branches to the medulla oblongata and supplies the 

 chorioid tela of the fourth ventricle. 



The internal cerebellar veins bring the blood from the interior 

 of the organ and pour it into the superior and inferior external veins. 



The superior external cerebellar veins (vena cerebelli supe- 

 riores) converge forward into a medial vein, which empties into 

 the great cerebral vein, and several lateral veins, which end in the 

 transverse or the superior petrosal sinus. 



The inferior external cerebellar veins (vena cerebelli infe- 

 riores] also form one small medial vein, which runs backward 

 and upward either into the straight or transverse sinus, and a 

 number of lateral veins. The lateral inferior cerebellar veins 

 terminate in the inferior petrosal and in the occipital sinus. 



