THE SINUSES OF THE CRANIUM. 523 



forwards over the jugular process of the occipital bone to the posterior compartment 

 of the jugular foramen. It is joined by veins from the posterior part of the cere- 

 brum, from both surfaces of the cerebellum, and from the diploe, as well as, at the 

 point where it turns downwards from the tentorium, by the superior petrosal sinus. 

 Emissary veins passing through themastoid and posterior condylar foramina connect 

 the lateral sinus with the veins of the exterior of the head. 



The occipital sinus is a small vessel, generally single, but sometimes double, 

 which is contained in the falx cerebelli. Above, it opens into the torcular Hero- 

 phili ; below, it communicates with the posterior spinal veins, _an<L is usually 

 continued forwards on one or both sides of the foramen magnum to join the lower 

 end of the lateral sinus. It receives one or two small veins from the cerebellum. 



The cavernous sinuses, placed one on each side of the body of the sphenoid 

 bone, and extending from the inner end of the sphenoidal fissure to the apex of the 

 petrous part of the temporal bone, are of considerable size and of very irregular 

 form. Their cavity is traversed by numerous interlacing filaments, which give rise 

 to a structure resembling that of cavernous tissue, and from this circumstance they 

 derive their name. Enclosed in the outer wall of each are the third, the fourth and 

 the ophthalmic and superior maxillary divisions of the fifth nerves as they pass 

 forwards to the sphenoidal fissure and foramen rotundum ; and in the cavity of the 

 sinus, covered only by its thin lining membrane, are the internal carotid artery, the 

 sixth nerve and a plexus of the sympathetic. Each sinus receives the ophthalmic 

 veins anteriorly, and communicates internally 



by means of the intercavernous sinuses with SBJP? ^-~. , N VE 



the corresponding vessel of the opposite side, n _ ! Hfcflfex ., M 

 while posteriorly it discharges its blood into 

 the petrosal sinuses. It is also joined by 

 some inferior cerebral veins, and by a small 

 vessel named the spheno - parietal sinus 

 (Breschet), which, after receiving a branch 

 from the dura mater and communicating with 

 the middle meningeal veins, runs inwards on Fig> ^TRANSVERSE SECTION OF THE 

 the under surface of the small wing of the CAVERNOUS SINUS. (Langer.) 



sphenoid bone. 



The circular sinus is the name given to a venous ring surrounding the pituitary 

 body in the sella turcica, and formed by two transverse vessels (anterior and posterior 

 intercavernous sinuses) which connect together the right and left cavernous sinuses. 

 Either of these transverse branches may however be wanting, but the anterior, 

 which is usually the larger, is the more constant. On the other hand, there is often 

 an additional vessel passing across below the pituitary body. 



The superior petrosal sinus is a narrow canal running in the groove along 

 the upper margin of the petrous part of the temporal bone. Commencing at the 

 back part of the cavernous sinus, it is directed outwards and backwards in the 

 attached margin of the tentorium cerebelli, and ends in the lateral sinus as this 

 turns downwards in the groove on the mastoid part of the temporal bone. It is 

 joined by some inferior cerebral and superior cerebellar veins, as well as by small 

 branches from the tympanum, which issue by the petro-squamous fissure. 



The inferior petrosal sinus, much shorter and wider than the superior, passes 

 from the cavernous sinus downwards and outwards in the groove between the lower 

 margin of the petrous bone and the basilar process of the occipital bone. It passes 

 through the anterior compartment of the jugular foramen and opens immediately 

 into the upper end of the internal jugular vein. The inferior petrosal sinus receives 

 some inferior cerebellar veins, and the auditory veins from the internal ear. 



The transverse or basilar sinus, or basilar plexus, is a venous network 



,^^ -OPHTH. NERVE 



INT. CAR. ART. 



" SUP. MAX. NERVE 



