POSTERIOR CEREBRAL ARTERY. 317 



The Lateral spinal branches enter the invertebral 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 fossae, and to the falx cerebelli. One 

 branch, described by Soemmering, passes into the cranium along the 

 first cervical nerve. 



The Anterior 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 pos- 

 terior 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 

 fourth ventricle. 



The Inferior cerebellar arteries wind around the upper part of the 

 medulla oblongata to the under surface of the cerebellum, to which 

 they are distributed. They pass between the filaments of origin of 

 the hypoglossal nerve in their course, and anastomose with the supe- 

 rior 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 border 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 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 dis- 

 tributed to the posterior lobes of the cerebrum. They are separated 

 from the superior cerebellar artery, 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 re- 

 ceive the posterior communicating arteries from the internal carotid. 

 They also send a branch to the velum interpositum and plexus cho- 

 roides. 



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 remarkable communication at the base of the brain is 



