360 ANATOMY OF THE RABBIT 



margin of the medulla. The trunk of the accessorius 

 extends backward on the spinal cord, its roots, about ten 

 in number, arising as far back as the fifth cervical spinal 

 nerve. It is an efferent nerve, while the two former are 

 mixed nerves to various visceral organs. 



{m) The twelfth cranial, or hypoglossal nerve (n. hypoglossus), 

 which controls the movements of the tongue, arises by 

 several roots from the ventral surface of the more posterior 

 part of the medulla oblongata at the lateral margin of 

 the pyramid, its point of origin corresponding to that of 

 the ventral root of a spinal nerve. 

 5. The arteries of the brain may be traced on its ventral surface 



as follows: 



(a) The basilar artery (a. basilaris) is a median trunk formed 

 on the ventral surface of the medulla oblongata by the 

 union of the vertebral arteries, the latter here represented 

 by their cut ends. It passes forward as far as the anterior 

 edge of the pons, giving off an irregular series of transversely 

 directed branches on the surface of the brain as well as 

 median branches which are concealed from view as they 

 run directly dorsad into the brain substance. 



{b) The inferior cerebellar artery (a. cerebelli inferior) is the 

 largest of the transverse branches arising from the basilar 

 on the ventral surface of the hindbrain. It originates about 

 half way along the basilar artery and passes laterad and 

 up the side of the brain to the posterior part of the cerebel- 

 lum. 



(c) The posterior cerebral artery (a. cerebri posterior) is 

 a paired vessel formed at the level of the anterior margin 

 of the pons by the bifurcation of the basilar. It passes 

 at each side laterad and dorsad to the posterior portion of 

 the cerebral hemisphere, giving secondary branches to the 

 diencephalon. 



{d) The superior cerebellar artery (a. cerebelli superior) is a 

 relatively large branch of the posterior cerebral, arising 

 near the origin of the latter and passing to the anterior 

 portion of the cerebellum after giving branches to the 

 midbrain. 



