286 



CIRCLE OF WILLIS. 



lates with the subscapular artery, a branch of the axillary. In its 

 course across the neck it passes in front of the scalenus anticus, 

 and across the brachial plexus ; in the rest of its. course it is covered 

 in by the trapezius, levator anguli scapulae, rhomboideus minor, and 

 rhomboideus major muscles. Sometimes it passes behind the 

 scalenus anticus, and between the nerves which constitute the 

 brachial plexus. This artery, which is very irregular in its origin, 

 proceeds more frequently from the third portion of the subclavian 

 artery than from the first. 



Fig. 105 * 



The posterior scapular gives branches to the neck, and opposite 

 the angle of the scapula inosculates with the profunda ceryicis. It 

 supplies the muscles along the posterior border of the scapula, and 

 establishes an important anastomotic communication between the 

 branches of the external carotid, subclavian, and axillary arteries. 



* The circle of Willis. The branches of the arteries have references only on one 

 side, on account of their symmetrical distribution. 1. The vertebral arteries. 2. The 

 two anterior spinal branches uniting to form a single vessel. 3. One of the posterior 

 spinal arteries. 4. The posterior meningeal. 5; The inferior cerebellar. 6. The 

 basilar artery giving off its transverse branches to either side. 7. The superior cere- 

 bellar artery. 8. The posterior cerebral. 9. The posterior communicating branch of 

 the internal carotid. 10. The internal carotid, showing the curvatures it makes within 

 the skull. 11. The ophthalmic artery divided across. 12. The middle cerebral artery. 

 13. The anterior cerebral arteries connected by, 14. The anterior communicating 

 artery. 



