060 



THE VEINS. 



the inner extremity of the sphenoidal fissure and terminates in the cavernous 

 sinus. 



The Inferior Ophthalmic Vein. Sometimes the veins from the floor of the orbit 

 collect into a separate trunk, the inferior ophthalmic vein, which either passes out 

 of the orbit through the spheno-maxillary fissure to join the pterygoid plexus of 

 veins, or else, passing backward through the sphenoidal fissure, it enters the 

 cavernous sinus, either by a separate opening or in common with the ophthalmic 

 vein. 



The Circular Sinus is formed by two transverse vessels which connect together 

 the two cavernous sinuses, the one passing in front and the other behind the 

 pituitary body, and thus forming with the cavernous sinuses a venous circle around 

 the body. The anterior one is usually the larger of the two, and one or other is 

 occasionally found to be absent. 



The Superior Petrosal Sinus is situated along the superior border of the petrous 

 portion of the temporal bone, in the front part of the attached margin of the 

 tentorium. It is small and narrow, and connects together the cavernous 



Opening of mastoid 

 vein. 



1 Torcular HerophiK. 

 FIG. 385. The sinuses at the base of the skull. 



and lateral sinuses at each side. It receives a cerebellar vein (anterior lateral 

 cerebellar) from the anterior border of the cerebellum, and a vein from the 

 internal ear. 



The Inferior Petrosal Sinus is situated in the groove formed by the junction of 

 the posterior border of the petrous portion of the temporal with the basilar process 

 of the occipital. It commences in front at the termination of the cavernous sinus, 

 and behind joins the lateral sinus after it has passed through the jugular foramen, 

 the junction of these two sinuses forming the commencement of the internal 

 jugular vein. 



The junction of the two sinuses takes place at the lower border of, or just 

 external to, the jugular foramen. The exact relation of the parts to one another 

 in the foramen is as follows : The inferior petrosal sinus is in front, with the 

 meningeal branch of the ascending pharyngeal artery, and is directed obliquely 

 downward and backward ; the lateral sinus is situated at the back part of the fora- 



