278 Anatomy of the Rabbit. 



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 lattpr here represented by 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 cinereum. 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 

 continuation 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. 



5. By dividing the supports of the cerebellum on either side, 

 the entire structure may be removed and the surface exposed, as in 

 Fig. 86, for an examination of the structures of the dorsal surface of 

 the rhombencephalon. The posterior medullary velum is removed 

 with the cerebellum, but a small, portion of the anterior medullary 

 velum should remain in place. 



(a) The fourth ventricle (ventriculus quartus) is the exten- 

 sive space enclosed by the rhombencephalon. It is con- 



