174 



DISSECTION OF THE BRAIN. 



brain. Define first the two arteries lying in the median fissure and join- 

 ing by a short branch ; next, an artery that passes outwards transversely 

 in the fissure of Sylvius, and pursue it to the outer surface of the hemis- 

 phere. Look then for a much smaller vessel (choroid), which enters into 

 the brain substance on the outer side of the crus cerebri. By gently 

 raising the cerebellum on the same side, the last artery of the cerebrum 

 may be traced back along the inner aspect of the hemisphere. 



Two arteries pass out to the small brain. One on the upper surface 

 may be brought into view on raising the cerebellum ; and care is to be 

 taken of the slender fourth nerve which lies by its side. The other artery 

 turns inwards to the median hollow of the cerebellum, and may be easily 

 followed. 



ARTERIES OF THE BRAIX (fig. 52). The brain is supplied with blood 

 by the vertebral and internal carotid arteries. 



The VERTEBRAL ARTERY, 12 , is a branch of the subclavian trunk (p. 

 77), and enters the trunk through the foramen magnum ; directed upwards 

 round the medulla oblongata, it blends with its fellow in a common trunk 

 (basilar) at the lower border of the pons. As the vessel winds round the 

 upper part of the cord, it lies between the roots of the suboccipital and 

 hypoglossal nerves ; but it is afterwards internal to the last. 



Fig. 52. 



1. Internal carotid trunk. 



2. Anterior cerebral branch. 



3. Anterior communicating. 



4. Middle cerebral branch. 



5. Choroidal branch. 



6. Posterior communicating. 



7. Posterior cerebral branch. 



8. Upper cerebellar branch. 



9. Internal auditory branch. 



10. Inferior cerebellar branch. 



11. Basilar artery. 



12. Vertebral artery. 



13. Anterior spinal branch. 



ARTERIES AT THE BASE OP THE BRAIN. 



Branches. Between its entrance into the spinal canal and its termina- 

 tion, each artery furnishes offsets to the spinal cord, the dura mater, and 

 the cerebellum. 



a. The posterior spinal branch is of inconsiderable size, and arises 

 opposite the posterior part of the medulla : it descends along the side of 

 the cord, behind the nerves, and anastomoses with its fellow, and with 

 branches that enter by the intervertebral foramina. 



b. The anterior spinal branch ( I8 ) is small like the preceding, and 

 springs from the artery opposite the front of the spinal cord. It joins the 

 corresponding twig on the opposite side, and the resulting vessel is con- 

 tinued along the middle of the cord on the anterior aspect. 



c. The posterior meningeal artery leaves the vertebral trunk opposite 



