ANGIOLOGY 241 



gemina, and anteriorly the longitudinal basilar vein or vena basilaris 

 media, of the cerebrum, which comes out of the anterior annular 

 venous sinus. The anterior annular venous sinus surrounds the Ease 

 of the olfactory nerves. It communicates with the sinus petrosus 

 sphenoideus, which emerges from behind the optic lobe, the sinus 

 temporo-sphenoideus, which emerges from in front of the optic lobe, 

 and posteriorly the median longitudinal vein of the medulla ob- 

 longata or vena basilaris. Laterally and anterior to the optic lobe 

 it receives the vena basilaris lateralis, and also a branch of the 

 vena ophthalmica. 



The blood received by the sinus annularis basilaris comes from 

 the brain cavity through three pairs of veins, as follows: first, the 

 two ophthalmic veins which pass through the posterior orbital wall 

 between the olfactory and the optic nerve; second, two other bran- 

 ches of the ophthalmica which pass with the optic nerve; third, two 

 veins which pass through a foramen by the side of the sella turcica 

 to the hypophysis together with the carotis cerebralis, and then 

 leave the cerebral cavity ventrally, at which point they are called 

 the venae carotes. These last accompany the cerebral artery back- 

 ward, and pass through a foramen in the base of the cranium. 

 Each one then passes through the cranial wall close to the external 

 auditory canal, and empties into another vein in the posterior re- 

 gion of the head. 



The sinus fovae hemispherii cerebelli lies in the hollow between 

 the os petrosum and the semicircular canals. It receives blood from 

 the external occipital sinus and from the cerebellum, and empties 

 into the vena auris interna. 



VEINS OF THE BRAIN CAVITY 



The vena auris interna passes through a bony canal along the 

 outer rim of the posterior semicircular canal and then a ong the 

 external semicircular canal. It -receives vessels from the labyrinth, 

 and extends along the posterior rim of the tympanum to the outer 

 ear canal. 



The vena occipitalis interna, extending from the sinus foraminis 

 occipitalis, passes through the side of the atlas and divides near the 

 condyle into two branches. One of these branches the internal 

 occipital, forms the root of the vena vertebralis, and the other 

 empties into the vena occipitalis externa. 



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