340 



SUPERIOR PETROSAL SINUSES. 



lobes, the inferior cerebellar veins, the superior petrosal sinuses, the mas- 

 toid, and posterior condyloid veins, and at their termination, the inferior 

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

 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 structure similar to 

 that of the corpus cavernosum penis. 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 inteinal 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 oph- 

 thalmic 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 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 con- 

 tinuations of the cavernous sinuses back- 

 wards along the lower border of the petrous 

 portion 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 (sinus of Ridley) is 

 situated in the sella turcica, surrounding the 

 pituitary gland, and communicating on each 

 side with the cavernous sinus. The poste- 

 rior segment is larger than the anterior. 



The Superior petrosal sinuses pass ob- 

 liquely backwards along the attached border 

 of the tentorium, on the upper margin of the 

 petrous portion of the temporal bone, and 

 establish a communication between the ca- 

 vernous and lateral sinus at each side. They 

 receive one or two cerebral veins from the 

 inferior part of the middle lobes, and a cerebellar vein from the anterior 

 border of the cerebellum. Near the extremity of the petrous bone these 

 sinuses cross the oval aperture which transmits the fifth nerve. 



* The sinuses of the base of the skull. 1. The ophthalmic veins. 2. The cavernous 

 amus of one side. 3. The circular sinus ; the figure occupies the position of the pituitary- 

 gland in the sella turcica. 4. The inferior petrosal sinus. 5. The transverse or ante- 

 rior occipital sinus. 6. The superior petrosal sinus. 7. The internal jugular vein. 

 8. The foramen magnum. 9. The occipital sinuses. 10. The torcular Herophili. 11. 

 1 . The lateral sinuses. 



