VENOUS SINUSES OF THE CRANIUM. 



463 



pital protuberance to the forameu jugulare. The sinus of the right side is 

 usually larger than that of the left ; both commence at the torcular Hero- 

 phili, and terminate in the jugular veins. The lateral sinuses receive the 

 blood transmitted from both the longitudinal sinuses, from the straight and 

 occipital sinuses, from the veins upon the sides and base of the brain, from 

 those on the under surface of the cerebellum, and from some of the veins of 

 the diploe. The petrosal sinuses also join the lateral sinus on each side : 

 and two emissary veins connect these with the veins at the back of the head 

 and neck. 



Fig. 314. SKETCH OF THE A'ENOUS SINUSKS Fig. 314. 



IN THE BASE OP THE CRANIUM, WITH THE 

 OPHTHALMIC VEIN. 



a, sella turcica and circular sinus ; 6, 

 cavernous sinus receiving c, the ophthalmic 

 vein ; d, superior petrosal ; e, inferior petrosal 

 sinus; /, transverse sinus; g, occipital; h, 

 lateral ; i, termination of the superior longi- 

 tudinal in the torcular Herophili. 



The posterior occipital sinus is some- 

 times a single canal, not unfrequently 

 double, as if composed of two com- 

 partments. It lies along the attached 

 border of the falx cere belli, extending 

 from the posterior margin of the fora- 

 men magnum to the confluence of the 

 sinuses. It communicates in front 

 with the posterior spinal plexuses of 

 veins. 



The sinuses placed at the base of the 

 skull are as follows, taking them in their order from before backwards. 



The circular sinus has the form of a ring, and is placed superficially in the 

 margin of the dura mater round the pituitary body ; it receives the blood 

 from the minute veins of the pituitary body, and communicates at each side 

 with the cavernous sinus. Sometimes it is only partially developed, the part 

 in front of the gland being that usually present : sometimes, however, it is 

 behind the gland. 



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

 bone, over the bases of the great wings, and stretching from the sphenoidal 

 fissure to the apex of the petrous portion of the temporal bones, are of con- 

 siderable size, and of very irregular form. Each receives the ophthalmic vein 

 at its fore part, and communicates internally with the circular sinus, and 

 posteriorly with the petrosal sinuses. In the wall of each, separated by the 

 lining membrane from the cavity of the sinus, pass forward the third, 

 fourth, and sixth cranial nerves, the ophthalmic division of the fifth nerve, 

 and the internal carotid artery. 



The upper petrosal sinus is a narrow canal running 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 teutorium cerebelli ; and, descending a little, ends 

 in the lateral sinus where this lies upon the temporal bone. 



The lower petrosal sinus, wider than the upper, passes downwards and 

 backwards along the inferior margin of the petrous bone, between this and 



