190 Anatomy of tiiij Rabbit. 



(j) The sixth cranial, or abducent nerve (n. abducens), is a slender 

 cord arising at the anterior end of the pyramid. 



(k) The seventh cranial, or facial nerve (n. facialis), and the 

 eighth, or acoustic nerve (n. acusticus), arise from the lateral 

 margin of the trapezoid body. 



The two nerves are closely associated, the former being slightly 

 anterior in position. Its chief portion is the motor root. In addition 

 the nerve receives a sensory filament, the portio intermedia or 

 intermediate nerve. 



(1) The glossopharyngeus, vagus, and accessorius arise by several 

 roots arranged in a linear series along the lateral margin of 

 the medulla. The trunk of the accessorius extends back- 

 ward on the spinal cord, its roots, about ten in number, 

 arising as far back as the fifth cervical spinal nerve. 



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

 arises by several roots from the ventral surface of the medulla 

 and at the lateral margin of the pyramid, its point of origin 

 corresponding to that of the ventral root of a spinal nerve. 



4. 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 bv their 

 cut ends. 



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

 largest of several transverse vessels arising from the basilar 

 and passing laterad to the cerebellum. 



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

 on either side at the level of the anterior margin of the pons 

 by the division of the basilar. It passes to the posterior 

 portion of the cerebral hemisphere. 



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

 branch of the posterior cerebral, passing to the anterior 

 portion of the cerebellum. 



(e) The cut end of the internal carotid artery lies on either side 

 of the tuber cenereum. It is connected backwards with the 

 posterior cerebral. 



(f) The middle cerebral artery (a. cerebri media) is given off 

 from the internal carotid, passing to the middle portion of 

 the hemispheres. 



(g) The anterior cerebral artery (a. cerebri anterior), the con- 

 tinuation of the carotid, passes to the anterior portion of 

 the ventral surface and the olfactory bulb. The anterior 

 cerebral is connected with that of the other side, a complete 

 anastomotic loop being formed around the hypothalamus by 

 combined branches of the vertebral and carotid arteries. 

 This is the circle of Willis. 



