BASILAR ARTERY 297 



f Lateral spinal, 



Posterior meningeal, 

 Vertebralj \ Anterior spinal, 



Posterior spinal, 

 [ Inferior cerebellar. 



f Transverse, 



Basilar, < Superior cerebellar, 

 [ Posterior cerebral. 



The Lateral spinal branches enter the intervertebral foramina, and are 

 distributed to the spinal cord and to its membranes. Where the vertebral 

 artery curves around the articular process of the atlas, it gives off several 

 muscular branches. 



The Posterior meningeal are one or two small branches which enter the 

 cranium through the foramen magnum, to be distributed to the dura mater 

 of the cerebellar fossaB, and to the falx cerebelli. One branch, described 

 by Soemmering, passes into the cranium along the first cervical nerve. 



The interior spinal is a small branch which unites with its fellow of the 

 opposite side, on the front of the medulla oblongata. The artery formed 

 by the union of these two vessels, descends along the anterior aspect of 

 the spinal cord, to which it distributes branches. 



The Posterior spinal winds around the medulla oblongata to the poste- 

 rior aspect of the cord, and descends on either side, communicating very 

 freely with the spinal branches of the intercostal and lumbar arteries. 

 Near its commencement it sends a branch upwards to the four ventricle. 



The Inferior cerebellar arteries wind around the upper part of the me- 

 dulla oblongata to the under surface of the cerebellum, to which they are 

 distributed. They pass between the filaments of origin of the hypo- 

 glossal nerve in their course, and anastomose with the superior cerebellar 

 arteries. 



The Transverse branches of the basilar artery supply the pons Varolii, 

 and adjacent parts of the brain. One of these branches, larger than the 

 rest, passes along the crus cerebelli, to be distributed to the anterior bor- 

 der of the cerebellum. This may be called the middle cerebellar artery. 



The Superior cerebellar arteries, two of the terminal branches of the 

 basilar, wind around the crus cerebri on each side, lying in relation with 

 the fourth nerve, and are distributed to the upper surface of the cerebellum, 

 inosculating with the inferior cerebellar. This artery gives off a small 

 branch, which accompanies the seventh pair of nerves into the meatus 

 auditorius internus. 



The Posterior cerebral arteries, the other two terminal branches of the 

 basilar, wind around the crus cerebri at each side, and are distributed to 

 the posterior lobes of the cerebrum. They are separated from the supe- 

 rior cerebellar arteries, near their origin, by the third pair of nerves, and are 

 in close relation with the fourth pair, in their course around the crura 

 cerebri. Anteriorly, near their origin, they give off a tuft of small vessels, 

 which enter the locus perforatus, and they receive the posterior communi- 

 cating arteries from the internal carotid. They also send a branch to the 

 velum interpositum and plexus choroides. 



The communications established between the anterior cerebral arteries 

 in front, and the internal carotids and posterior cerebral arteries behind, 

 by the communicating arteries, constitute the circle of Willis. This 



