SINUSES OF THE DURA MATER. 



465 



by several small veins around the posterior margin of the foramen magnum, which 

 communicate with the posterior spinal veins, and terminate by separate openings 

 (sometimes by a single aperture) in the torcular Herophili. 

 2. The sinuses at the base of the skull are the 



Cavernous. Inferior petrosal. 



Circular. Superior petrosal. 



Transverse. 



The Cavernous Sinuses are named from their presenting a reticulated structure. 

 They are two in number, of large size, and placed one on each side of the sella 

 Turcica, extending from the sphenoidal fissure to the apex of the petrous portion. 



Fig. 239. The Sinuses at the Base of the Skull. 



of the temporal bone : they receive anteriorly the ophthalmic vein through the 

 sphenoidal fissure, communicate behind with the petrosal sinuses, and with each 

 other by the circular and transverse sinuses. On the inner wall of each sinus is 

 found the internal carotid artery, accompanied by filaments of the carotid plexus 

 and by the sixth nerve ; and on its outer wall, the third, fourth, and ophthalmic 

 nerves. These parts are separated from the blood flowing along the sinus by the 

 lining membrane, which is continuous with the inner coat of the veins. The 

 cavity of the sinus, which is larger behind than in front, is intersected by filaments 

 of fibrous tissue and small vessels. The cavernous sinuses receive the inferior 

 anterior cerebral veins ; they communicate with the lateral sinuses by means 

 of the superior and inferior petrosal, and with the facial vein through the 

 ophthalmic. 



The ophthalmic is a large vein, which connects the frontal vein at the inner 

 angle of the orbit with the cavernous sinus ; it pursues the same course as the 

 ophthalmic artery, and receives branches corresponding to those derived from that 

 vessel. Forming a short single trunk, it passes through the inner extremity of 

 the sphenoidal fissure, and terminates in the cavernous sinus. 



The Circular Sinus completely surrounds the pituitary body, and communicates 

 on each side with the cavernous sinuses. Its posterior half is larger than the 

 30 



