718 



DISSECTION OF THE BRAIN. 



of large 

 brain, 



and of small 

 brain. 



on the medulla oblongata, and those of the carotid near the median 

 fissure of the large brain, the student should lay bare on one side the 

 branches to the large brain. Define first the two arteries (anterior cere- 

 bral) lying in the median fissure ( 2 ) and joined by a short branch ( 3 ) 

 (anterior communicating) ; next, an artery that passes outwards ( ') in 

 the fissure of Sylvius (middle cerebral), and pursue it to the outer sur- 

 face of the hemisphere. Look then for a much smaller vessel (anterior 

 choroid) which sinks into the brain on the outer side of the cms 

 cerebri ( 5 ). Then by gently raising the cerebellum on the same side, 

 the last artery of the cerebrum (posterior cerebral, 7 ) may be traced back 

 round the crus cerebri to the inner part of the hemisphere. 



Two principal arteries pass to the cerebellum. One on the upper 

 surface (superior cerebellar) may be brought into view just behind the 

 bifurcation of the basilar artery ( 8 ) and separated from the posterior 

 cerebral by the third nerve. The fourth nerve runs beside it, and 

 the cerebellum should be raised in tracing the vessel. Two other 

 arteries (anterior and posterior inferior cerebellar) turn backwards 

 and outwards from the vertebral, and may be easily followed. 



The branches of the anterior, middle and posterior cerebral arteries 

 will be followed out as they are described by removing the adhering 

 membranes, by gently opening the fissures and sulci in which they 

 partially lie, and by drawing them and their branches away from the 

 brain substance as the work proceeds, and if care is taken no material 

 injury will be done. 



ARTERIES OF THE BRAIN (fig. 257). The brain is supplied with 

 blood by the vertebral and internal carotid arteries. 



The VERTEBRAL ARTERY ( 12 ) is a branch of the subclavian trunk 

 and enters the skull through the foramen magnum ; directed 

 upwards and forwards round the medulla oblongata, it blends with 

 its fellow in a common trunk (BASILAR) at the lower border of the 

 winds round pons. As the vessel winds round the medulla oblongata, it lies 

 between the roots of the first cervical and hypoglossal nerves ; but it 

 is afterwards internal to the latter. 



BRANCHES. Between its entrance into the spinal canal and its 

 termination in the basilar, each artery furnishes offsets to the dura 

 mater, to the spinal cord, and to the cerebellum. 



a. The posterior meningeal branch leaves the trunk opposite the 

 foramen magnum, and ramifies in the dura mater lining the cere- 

 bellar fossa of the occipital bone. 



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

 opposite the back of the medulla oblongata : 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. 



c. The anterior spinal branch ( 13 ) is small like the preceding, and 

 springs from the trunk opposite the front of the medulla. It joins the 

 corresponding twig of the opposite side, and the resulting vessel is 

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



and to under d. The posterior inferior cerebellar artery ( 10 ) arises from the end of 

 cerebellum, the vertebral (sometimes from the basilar), and winds backwards 



Arteries of 

 the brain. 



Vertebral 



ends in 

 basilar, 





branches 



to dura 

 mater : 



to spinal 

 cord, 



posterior 

 and 



anterior: 



