THE ARTERIES 133 



of the squamous temporal bone. Passing through the mastoid 

 foramen into the parieto-temporal canal, it there anastomoses 

 with the great meningeal or spheno-spinous artery. 



(3) The retrograde branch, or ramus anastomoticus, passes back- 

 wards through the posterior foramen of the wing of the atlas to 

 anastomose with the vertebral artery. 



Terminal Branches of the Occipital Artery. 



(i) The occipito-muscular artery. — This takes a course upwards 

 towards the occipital crest, and it is distributed to the muscles in 

 the region of the poll. 



(2) The cerebrospinal artery. — This division of the occipital 

 enters the spinal canal through the antero-internal foramen of the 

 atlas. It then divides into two parts, one of which runs forwards 

 and the other backwards. 



The anterior division joins its fellow of the opposite side and 

 forms the basilar artery^ which enters the cranial cavity through 

 the foramen magnum. It passes along the inferior aspect of the 

 medulla oblongata to the pons variolii, where it divides into the 

 posterior cerebral arteries, which enter into the formation of the 

 Circle of Willis. 



The posterior division of the cerebro-spinal artery inosculates 

 with its fellow of the opposite side to form the median spinal 

 artery. 



The External Carotid Artery. — This vessel passes along the wall of the 

 guttural pouch, where it is covered by the stylo-maxillaris, the upper 

 belly of the digastricus and the stylo-hyoid muscles. It emerges from 

 between the anterior border of the last-named muscle and the posterior 

 border of the long cornu of the hyoid bone. It then traverses the outer 

 surface of the cornu for a short distance, and divides into the superficial., 

 temporal., and internal maxillary arteries. 



