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) 
(b) 
(c) 
(d) 
(e) 
(g) 
5. 
The basilar artery (a. basilaris) isa 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. 
The inferior cerebellar artery (a. cerebelli inferior) is the 
largest of several transverse vessels arising from the basilar 
and passing laterad to the cerebellum. 
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. 
The superior cerebellar artery (a. cerebelli superior) is a 
branch of the posterior cerebral, passing to the anterior 
portion of the cerebellum. 
The cut end of the internal carotid artery lies on either 
side of the tuber cinereum. It is connected backwards with 
the posterior cerebral. 
The middle cerebral artery (a. cerebri media) is given off 
from the internal carotid, passing to the middle portion of 
the hemispheres. 
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. 
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- 
