THE SISl'SES OF THE DURA JfATER. 



jugular vein (Fig. 386). They communicate with the veins of the pericranium 

 by means of the mastoid and posterior condyloid veins, and thev receive 

 some of the inferior cerebral and inferior cerebellar veins and some veins from 

 the diploe. 



The Occipital is the smallest of the cranial sinuses. It is generally single, but 

 occasionally there are two. It is situated in the attached margin of the falx cere- 

 belli. It commences by several small veins around the margin of the foramen 

 magnum, one of which joins the termination of the lateral sinus ; it communicates 

 with the posterior spinal veins and terminates in the torcular Herophili. 



The sinuses at the base of the skull are the 



Cavernous. Superior Petrosal. 



Circular. Inferior 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 



Dura mater limn 



^Lining membrane of sinus. 

 "Third nerte. 



nerve. 

 Internal carotid. 



r ^^^^ fourth nerve, 



First division of fifth nerve, 





FIG. 3S4. Plan showing the relative position of the structures in the right cavernous sinus, viewed from 

 behind. 



turcica. extending from the sphenoidal fissure to the apex of the petrous portion 

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

 sphenoidal fissure, and open behind into the petrosal 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 division of the fifth nerve. 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 some of the cerebral veins : they communicate with the lateral 

 sinuses by means of the superior and inferior petrosal. and with the facial vein 

 through the ophthalmic. They also communicate with each other by means of the 

 circular sinus. 



Surgical Anatomy. An arterio-venous communication may be established between the 

 cavernous sinus and the carotid artery, as it lies in it. giving rise to a pulsating tumor in the 

 orbit. These communications may be the result of injury, such as a bullet wound, a stab, or a 

 blow or fall sufficiently severe to cause a fracture of the base of the skull in this situation, or 

 they may occur idiopathically from the rupture of an aneurism or a diseased condition of the 

 internal carotid artery. The disease begins with sudden noise and pain in the head, followed by 

 exophthalmic, and development of a pulsating tumor at the margin of the orbit, with thrill 

 and the characteristic bruit. In some cases the opposite orbit becomes affected by the passage 

 of the arterial blood into the opposite sinus by means of the circular sinus. Or the arterial 

 blood may find its way through the emissary veins (see page 663) into the pterygoid plexus, and 

 thence into the veins of the face. Pulsating tumors of the orbit may also be due to traumatic 

 aneurism of one of the orbital arteries, and symptoms resembling those of pulsating tumor may 

 be produced by pressure on the ophthalmic vein, as it enters the sinus, by an aneurism of the 

 internal carotid artery. 



The ophthalmic is a large vein which connects the angular vein at the inner 

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

 the ophthalmic artery, and receives tributaries corresponding to the branches 

 derived from that vessel. Forming a short single trunk, it passes through 



