LATERAL SINUSES. 333 



tion of the inferior longitudinal sinus to the torcular Herophili. It 

 receives the vense Galeni, the cerebral veins from the inferior part 

 of the posterior lobes, and the superior cerebellar veins. 



The Occipital sinuses are two canals of small size, situated in the 

 attached border of the falx cerebelli ; they commence by several 

 small veins around the foramen magnum, and terminate by separate 

 openings in the torcular Herophili. They not unfrequently commu- 

 nicate with the termination of the lateral sinuses. 



The Lateral sinuses, commencing at the torcular Herophili, pass 

 horizontally outwards, in the attached margin of the tentorium, and 

 curve downwards and inwards along the base of the petrous portion 

 of the temporal bone, at each side, to the foramina lacera posteriora, 

 where they terminate in the internal jugular veins. Each sinus rests 

 successively in its course upon the transverse groove of the occipital 

 bone, posterior inferior angle of the parietal, mastoid portion of the 

 temporal, and again on the occipital bone. They receive the cerebral 

 veins from the inferior surface of the posterior lobes, the inferior 

 cerebellar veins, the superior petrosal sinuses, the mastoid, and pos- 

 terior condyloid veins, and, at their termination, the inferior petrosal 

 sinuses. These sinuses are often unequal in size, the right being 

 much larger than the left. 



The sinuses of the base of the skull are the 



Cavernous, 

 Inferior petrosal, 

 Circular, 

 Superior petrosal, 

 Transverse. 



The Cavernous sinuses are named from presenting a cellular struc- 

 ture in their interior. They are situated on each side of the sella 

 turcica, receiving, anteriorly, the ophthalmic veins through the 

 sphenoidal fissures, and terminating posteriorly in the inferior petrosal 

 sinuses. In the internal wall of each cavernous sinus is the internal 

 carotid artery, accompanied by several filaments of the carotid plexus, 

 and crossed by the sixth nerve ; and, in its external wall, the third, 

 fourth, and ophthalmic nerves. These structures are separated from 

 the blood flowing through the sinus, by the tubular lining membrane. 

 The cerebral veins from the under surface of the anterior lobes, 

 open into the cavernous sinuses. They communicate by means of 

 the ophthalmic veins with the facial veins, by the circular sinus with 

 each other, and by the superior petrosal with the lateral sinuses. 



The Inferior petrosal sinuses are the continuations of the cavern- 

 ous sinuses backwards along the lower border of the petrous por- 

 tion of the temporal bone at each side of the base of the skull, to 

 the foramina lacera posteriora, where they terminate with the lateral 

 sinuses in the commencement of the internal jugular veins. 



The Circular sinus is situated in the sella turcica, surrounding the 

 pituitary gland, and communicates on each side with the cavernous 

 sinus. 



