238 PRACTICAL ANATOMY. 



THE BASILAR ARTERY. 



The basilar artery runs along the median line of the 

 under surface of the pons Varolii. It is formed by the 

 union of the two vertebral arteries and sends off : 



Anterior Cerebellar. Passes to the under surface of 

 cerebellum. 



Transverse. Four to six pairs distributed to inferior 

 surface of cerebellum. 



Superior Cerebellar. Pass around the crura and are 

 distributed to meninges. 



Posterior Cerebral. Two terminal ; wind around 

 the crura and anastomose with the middle cerebral. 



At the base of the brain is a vascular circle, the circle 

 of Willis. It is formed by nine vessels, the two pos- 

 terior cerebral (terminal branches of the basilar), the two 

 posterior communicating (branches of the internal caro- 

 tid), the two anterior cerebral (branches of the internal 

 carotid), the two internal carotids, and the anterior com- 

 municating between the two anterior cerebral arteries 

 within. This anastomosis surrounds the structures of the 

 interpeduncular space. 



THE THYROID AXIS. 



The thyroid axis sends off: 



Inferior Thyroid. Supplies the inferior portion of 

 the thyroid gland. It sends off the laryngeal, tracheal, 

 O3sophageal, and ascending cervical ; the last named 

 passes up the neck and anastomoses with the ascend- 

 ing pharyngeal. 



Supra-scapular. Runs across the neck over the 

 transverse ligament of the scapula and is distributed to 

 the supraspinatus 



Transversalis Colli. Runs transversely across the 

 neck to the vertebral border of the scapula, along 



