622 THE VEINS 



poral bone it leaves the tentorium and curves downwards and inwards and then 

 forwards over the jugular process of the occi])ital lione, and ends in the posterior 

 compartment of tlie jugular fossa in the sinus jugularis or bulb of the internal 

 jugular vein. The S-shaped })art of the sinus Avhich lies on the mastoid portion 

 of the temporal and jugular ])ortion of the occipital l^one is sometimes known 

 as the sigmoid sinus. The lateral sinus receives the veins from the temporo- 

 sphenoidal 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 external 

 parietal veins of the diploe, and at the spot where it leaves the tentorium the supe- 

 rior petrosal sinus and, Avhen present, the petro-squamous sinus. It communi- 

 cates with the occipital and vertebral veins through the mastoid and posterior 

 condyloid foramina by means of emissary veins. As the lateral sinus lies betAveen 

 the layers of the tentorium it is on section prismatic in shape. The sigmoid 

 portion is semicylindrical. 



The right lateral sinus is usually the larger and the direct continuation of the 

 superior longitudinal sinus, and hence conveys the chief part of the blood from 

 the cortical surface of the brain and vault of the skull. The left lateral sinus is 

 usually the smaller and the direct continuation of the straight sinus, and hence 

 returns the chief part of the blood from the central ganglia of the brain. 



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 opera- 

 tions of trephining the mastoid cells, opening the tympanum, and exposing the 

 sinus itself, in septic thrombosis, &c. The course of the sinus corresponds to a 

 line drawn from the external occipital protuberance to the base of the mastoid pro- 

 cess, or to the asterion, and thence over the back of the mastoid process in a 

 curved line towards its apex. 



(8) The superior petrosal sinus (figs. 387, 388) 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 lateral sinus. Leaving the 

 outer 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 lateral sinus as 

 the latter turns downwards on the mastoid portion of the temporal bone. It 

 receives veins from the temporo-sphenoidal lol^e of the cerebrum, veins from the 

 cerebellum, veins from the tympanum through the squamo-petrosal fissure, and 

 sometimes the fronto-parietal veins of the diploe. 



(9) The inferior petrosal sinus (figs. 387, 388) 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 con- 

 siderably wider. As it crosses the anterior compartment of the jugular foramen, it 

 separates the glosso-pharyngeal from the pneumogastric and spinal accessory 

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

 medulla and pons, and from the internal ear. The last issue through the aqueduc- 

 tus vestilmli and aqueductus cochleae. 



(10) The cavernous sinus (fig. 387) is an irregular shaped venous space 

 situated Ijetween the meningeal and periosteal layers of the dura mater on the side 

 of the body of the sphenoid bone. It extends from the central end of the sphe- 

 noidal fissure in front to the apex of the petrous bone behind. Its outer wall is the 

 more distinct, and contains in it, but separated from the blood by the lining mem- 

 l)rane of the sinus, the third and fourth nerves, and the ophthalmic division of 

 the fifth nerve, the nerves lying in the above-mentioned order frcim above down- 

 wards, and from witliin outAvards. The internal carotid artery and the sixth 

 nerve also pass through the sinus, being separated from the blood by the endothel- 

 ial lining. The inner wall is practically absent, the blood-space communicating 

 across the middle line with the opposite sinus in front, behind, and below the 

 pituitary body or hypophysis cerebri. (See Circul.\r Sixus. ) The cavernous 

 sinus is traversed by numerous trabecular or fibrous bands, so that there is no 

 central space, but rather a number of endothelially-lined irregular lacunar cavities 

 communicating with each other. Hence its name cavernous, from its resem- 

 blance to cavernous tissue. In front it receives the ophthalmic vein, witli which 

 it is practically continuous, and just above the third nerve the sinus ala3 parvse. 



