652 THE BLOOD-VASCULAR SYSTEM 



toid portion of the temporal bone it leaves the tentorium and curves medially 

 and downward and then forward over the jugular process of the occipital bone, 

 and ends in the posterior compartment of the jugular fossa in the superior bulb of 

 the internal jugular vein. The S-shaped part of the sinus which lies on the mas- 

 toid portion of the temporal and jugular portion of the occipital bone is sometimes 

 known as the sigmoid sinus. The transverse sinus receives the internal auditory 

 veins [vv. auditivse internee] from the labyrinth, which emerge from the internal 

 auditory meatus. It also receives veins from the temporal lobe of the cerebrum, 

 some of the superior and inferior cerebellar veins, some of the veins of the medulla 

 and pons, the occipital, and the posterior temporal and occipital veins of the diploe. 

 At the point where it leaves the tentorium it drains the superior petrosal sinus 

 and, when present, the petro-squamous sinus. It communicates with the occip- 

 ital and vertebral veins through the mastoid and posterior condjdoid foramina 

 by means of the mastoid and condyloid emissary veins. As the transverse sinus 

 lies between the layers of the tentorium it is on section prismatic in shape. 

 The sigmoid portion is semicylindrical. 



The right transverse sinus is usually the larger and the direct continuation of the superior 

 sagittal sinus, and hence conveys the chief part of the blood from the cortical surface of the brain 

 and vault of the skull. The left transverse sinus is usually the smaller and the direct con- 

 tinuation of the straight sinus, and hence returns the chief part of the blood from the central 

 ganglia of the brain. The right and left sinuses communicate opposite the internal occipital 

 protuberance. 



The relation of the lateral sinus to the outside of the skull, especially to the mastoid process 

 of the temporal bone, is of importance with reference to the operations of trephining the 

 mastoid cells, opening the tympanum, and exposing the sinus itself, in septic thrombosis, etc. 

 The course of the sinus corresponds to a line drawn from the external occipital protuberance 

 to the base of the mastoid process, or to the asterion, and thence over the back of the mastoid 

 process in a curved line toward its apex. 



(8) The superior petrosal sinus [sinus petrosus superior] (figs. 514, 515) 

 runs at the attached margin of the tentorium cerebelli, along the upper border 

 of the petrous portion of the temporal bone. It connects the cavernous with the 

 transverse sinus. Leaving the lateral and back part of the cavernous sinus just 

 below the fourth nerve, it crosses the fifth nerve, and, after grooving the petrous 

 bone, ends in the transverse sinus as the latter turns downward on the mastoid 

 portion of the temporal bone. It receives veins from the temporal lobe of the 

 cerebrum, veins from the cerebellum, veins from the tympanum through the 

 squamo-petrosal fissure, and sometimes the anterior temporal veins of the diploe. 



(9) The inferior petrosal sinus [sinus petrosus inferior] (figs. 514, 516) runs 

 along the line of the petro-occipital suture, and connects the cavernous sinus with 

 the commencement of the internal jugular vein. It is shorter than the superior 

 petrosal, but considerably wider. As it crosses the anterior compartment of the 

 jugular foramen, it separates the glosso-pharyngeal from the vagus and accessory 

 nerves. It receives veins from the inferior surface of the cerebellum, from the 

 medulla and pons, and from the internal ear. The last, the vein of the cochlear 

 canaliculus [v. canaliculi cochlear], issues through the canaliculus cochleae. 



(10) The cavernous sinus [sinus cavernosus] (fig. 516) is an irregularly shaped 

 venous space situated between the meningeal and periosteal layers of the dura 

 mater on the side of the body of the sphenoid bone. It extends from the medial 

 end of the superior orbital (sphenoidal) fissure in front to the apex of the petrous 

 bone behind. Its lateral wall is the niore distinct, and contains the third and 

 fourth nerves, and the ophthalmic division of the fifth nerve. The nerves take 

 the above-mentioned order from above downward, and in the medio-lateral direc- 

 tion. The internal carotid artery and the sixth nerve also pass through the sinus, 

 being separated from the blood by the endothelial lining. The right and left 

 cavernous sinuses communicate across the middle line with the opposite sinus in 

 front and behind the hypophysis cerebri as before mentioned. 



The cavernous sinus is traversed by numerous trabeculse or fibrous bands, so that there is 

 no contra! space, but rather a number of endothelial-lined irregular lacunar cavities commu- 

 nicating one another. Ilonce its name cavernous, from its resemblance to cavernous tissue. 

 In front it receives tlie ophthalmic vein, witii wl)ich it is practically continuous, and just 

 above the third nr-rvf; the spheno-parietal sinus. Medially it communicates with the opposite 

 sinus, and posteriorly it ends in the superior and inferior jjctrosal sinuses. It also receives 

 veins from the inferior surface of the frontal l()l)e of the brain, and some of the middle cerebral 

 veins. Through the Vesalian vein, which runs in a minute foramen in the spinous process of 



