144 TOPOGRAPHICAL ANATOMY OF THE 



from the osseous tentorium, where they are connected with the con- 

 fluens sinuum, to the inner end of the temporal meatus. Each sinus 

 leaves the cranium by the temporal meatus and is continued as the 

 dorsal cerebral vein, which unites with the superficial temporal. A 

 communicating sinus links the right and left sinuses together. The 

 occipiUd sinuses occupy that portion of the dura mater which coincides 

 in position with the grooves between the vermis and the hemispheres 

 of the cerebellum. In front they open into the communicating sinus 

 between the two transverse sinuses. Behind they are connected with 

 a vein that runs backwards into the vei'tebral canal dorsal to the 

 medulla oblongata. There are numerous intercommunications between 

 the right and left sinuses. The dorsal loetrosal sinuses run in the 

 tentorium cerebelli close to the projecting edge of the temporal bone, 

 and open into the transverse sinuses near the inner end of the temporal 

 meatus. Each petrosal sinus receives a rhinal vein at its anterior end. 



The right and left cavernous sinuses occupy groove-like depressions 

 at the junction of the body and temporal wings of the sphenoid bone, 

 immediately lateral to the sella turcica. Behind the sella turcica an 

 intercavernous sinus places the two cavernous sinuses in free com- 

 munication with each other. Occasionally, a very much smaller inter- 

 cavernous sinus occurs in front of the sella. Anteriorly each cavernous 

 sinus is continuous with a reflex vein, which places the sinus in com- 

 munication with the exterior of the cranium. The floor of each sinus is 

 connected by a wide oval opening with the ventral petrosal sinus of 

 that side. As has been previously noted, the oculomotor, abducent, 

 ophthalmic and maxillary nerves are related to the wall of the cavernous 

 sinus. Each ventral petrosal sinus is enclosed in the dense fibrous 

 tissue (dura mater) that occludes the irregular composite foramen 

 bounded by the occipital, temporal and sphenoid bones. The posterior 

 end of each sinus is dilated and lies in the condyloid fossa, where it 

 receives the condyloid vein and communicates with the ventral cerebral 

 vein. The main part of the sinus follows the margin of the basilar part 

 of the occipital bone and extends for a short distance under the 

 temporal wing of the sphenoid bone. Anteriorly it communicates with 

 veins in the pterygo-palatine fossa. The hasilar plexus lies on the 

 inner face of the basilar part of the occipital bone. Anteriorly it has 

 narrow communications with the cavernous and intercavernous sinuses, 

 and posteriorly it is continuous with veins within the atlas. The 

 condyloid vein forms a connection between the basilar plexus and the 

 ventral petrosal sinus. 



A. CAROTIS INTERNA. — The origin and extra-cranial course of the 

 internal carotid arterv have been noted at earlier stages of the dis- 



