202 



Arteria siibclavia. 



poster i 'ores 



A.profunda. 

 ~ cerebrt. 



546. Course of the Vertebral Arteries. 



View from behind, the vertebral canal being laid open. 



The branches arising from the basilar artery on each side are : the internal 

 auditory, Art. auditiva interna, passing through the internal auditory meatus to the 

 labyrinth, and the superior c e r e b e 1 1 a r, Art. cerebelli superior, to the upper 

 surface of the cerebellum. The posterior cerebral (Arteriae profundae cerebri], 

 unite with the posterior communicating arteries from the internal carotid, pass 

 backwards and upwards and supply the posterior lobes of the cerebrum. By the 

 anastomosis which exists between the branches of the internal carotid and ver- 

 tebral arteries at the base of the brain, the circle of Willis, Circidus arteriosus 

 WilUsii, is formed. The parts of the brain included within this circle are: the 

 Chiasma, Lamina, cinerea, Infundibulum, Tuber tinereum, Corpora albicantia and 

 posterior p e r f o rate d s p a c e. 



2. The internal mammary artery, Art. mammaria interna, arises from 

 the subclavian opposite the thyroid axis, and descends behind the clavicle to the 

 inner surface of the anterior wall of the chest. Its branches are: mediastinal, 

 thymic, anterior bronchial, p ericar diaco-phr enic to the diaphragm, 

 the anterior intercostal, two for each intercostal space, an upper, larger, 

 and a lower, smaller, perforating branches, Rami perforantes, to the skin 

 and muscles of the thorax, and in the female the external mammary artery 

 to the mamma. Between the sixth costal cartilage and xiphoid appendix, the inter- 

 nal mammary artery divides into the musculo -phrenic and superior epi- 

 gastric, which latter anastomoses with the inferior epigastric and crural arteries 

 (see Fig. 548). 



