ARTERIES OF THE BRAIN. 175 



the foramen magnum, and ramifies in the dura mater lining the fossa of 

 the occipital bone. 



d. The inferior cerebellar artery (posterior) ( 10 ) is distributed to the 

 under surface of the cerebellum. Taking origin from the end of the 

 vertebral, this branch winds backwards round the medulla between the 

 pneumogastric and spinal accessory nerves, to the median fissure of the 

 cerebellum. Directed onwards along the fissure the artery reaches the 

 upper surface of the small brain, and there anastomoses with the superior 

 cerebellar artery. 



An offset of this branch ramifies over the under part of the cerebellum, 

 and ends externally by anastomosing with the artery of the upper surface. 

 As the vessel lies by the side of the aperture of the fourth ventricle it gives 

 a small choroid offset to the plexus of that cavity. 



The BASILAR ARTERY ( n ), formed by the union of the two vertebrals, 

 reaches from the lower to the upper border of the pons, where it ends by 

 dividing into two branches (posterior cerebral) for the cerebrum. The 

 vessel touches the basilar process of the occipital bone, from that circum- 

 stance receiving its name, and lies in the median groove of the pons. On 

 each side of, and almost parallel to it, is the sixth nerve. 



Branches. Besides the tw.o terminal branches mentioned above, the 

 artery supplies transverse offsets to the pons and the under part of the 

 cerebellum, and a large branch to the upper surface of the cerebellum. 



a. The transverse arteries of the pons are four or six small twigs, which 

 are named from their direction, and are distributed to the substance of the 

 pons. One of them ( 9 ) gives an offset (auditory) to the internal ear along 

 the auditory nerve. 



b. Resembling this set of branches is the following artery, the inferior 

 cerebellar (anterior) : this arises from the basilar trunk, and extends to 

 the fore part of the under surface of the cerebellum, on which it is dis- 

 tributed. 



c. The superior cerebellar artery ( 8 ) is derived from the basilar so near 

 the termination as to be often described as one of the final branches of that 

 vessel. Its destination is to the upper surface of the small brain, to which 

 it is directed backwards over the third nerve and the crus cerebri, but 

 parallel with the fourth nerve. On the upper surface of the cerebellum 

 the artery spreads its ramifications, which anastomose with the vessel of 

 the opposite side, and with the inferior cerebellar artery. 



Some twigs of this vessel enter the piece of the pia mater (velum inter- 

 positum), which projects into the posterior part of the cerebrum. 



d. The posterior cerebral artery ( 7 ) takes on each side a backward 

 course, similar to that of the preceding artery, but separated from it by the 

 third nerve. The vessel is then applied to the inner surface of the cere- 

 brum, and divides into many branches : some of these supply the under 

 part, whilst others turn upwards on both the outer and inner surfaces 

 of the back of the hemisphere, and anastomose with the other cerebral 

 arteries. 



Near its origin it is joined by the posterior communicating artery of the 

 carotid ; and its branches to the brain are the following : 



Numerous small long branches leave it close to its origin, and enter the 

 base of the brain between the crura cerebri (posterior perforated spot). 



A small choroid artery (posterior) supplies the fold of pia mater that 

 projects into the cerebrum : this small branch is transmitted between the 



