726 THE VASCULAR SYSTEMS 



the temporal bone, and they unite with the inferior petrosal sinus, just external 

 to the jugular foramen, to form the internal jugular vein (Fig. 508). They com- 

 municate with the veins of the pericranium by means of the mastoid and posterior 

 condylar veins, and they receive some of the inferior cerebral and inferior cere- 

 bellar veins, some veins from the diploe, and often veins from the internal ear 

 (vv. audit ivae internae), which come out of the internal auditory meatus. The 

 petrosquamous sinus, when present, runs backward along the junction of the 

 petrous and squamous portions of the temporal bone, and opens into the lateral 

 sinus. 



Applied Anatomy. The lateral sinus may, as a result of middle-ear disease, be attacked by 

 suppurative inflammation, which leads to blocking (septic thrombophlebitis). In such a case 

 the surgeon will be obliged to open the sinus to remove the infected clot and tie the internal 

 jugular vein to intercept thrombi. The line overlying the sinus is as follows: Draw a line hori- 

 zontally outward from the occipital protuberance to a point one inch posterior to a vertical line 

 drawn through the external auditory meatus, and from this point drop a second line to the mastoid 

 process. 



The occipital sinus (sinus occipitalis) (Fig. 503) is the smallest of the cranial 

 sinuses. It is generally single, but occasionally there are two. It is situated in 

 the attached margin of the falx cerebelli. It commences by several small veins 

 around the margin of the foramen magnum, one of which joins the termination 

 of the lateral sinus; it communicates with the posterior spinal veins and terminates 

 in the torcular Herophili. 



The torcular Herophili, or confluence of the sinuses (confluens sinuum), is the 

 term applied to the dilated extremity of the superior sagittal sinus. It is of 'irreg- 

 ular form, and is lodged on one side (generally the right) of the internal occipital 

 protuberance. From it the lateral sinus of the side to which it is deflected is 

 derived. It also receives the blood from the occipital sinus, and is connected 

 across the middle line with the commencement of the lateral sinus of the opposite 

 side. 



The sinuses at the base of the skull are: 



Two cavernous sinuses. Two superior petrosal sinuses. 



Two sphenoparietal sinuses. Two inferior petrosal sinuses. 



Circular sinus. Transverse sinus. 



The cavernous sinuses (Figs. 507 and 508) are so named because they present 

 a reticulated structure, due to their being traversed by numerous interlacing 

 filaments (Fig. 505). They are of irregular form, larger behind than in front, 

 and are placed one on each side of the sella turcica, extending from the sphenoidal 

 fissure to the apex of the petrous portion of the temporal bone. Each cavernous 

 sinus (sinus cavernosus] receives anteriorly the superior ophthalmic vein through 

 the sphenoidal fissure, and opens behind into the petrosal sinuses. On the inner 

 wall of each sinus is the internal carotid artery, accompanied by filaments of the 

 carotid plexus and by the abducent nerve; and on its outer wall, the oculomotor, 

 rtrochlear, ophthalmic, and superior maxillary divisions of the trigeminal nerve 

 (Fig. 505). These parts are separated from the blood flowing along the sinus 

 by the lining membrane, which is continuous with the inner coat of the veins. 

 Each cavernous sinus receives some of the cerebral veins, and also the spheno- 

 parietal sinus. It communicates with the lateral sinus by means of the superior 

 petrosal sinus; with the internal jugular vein through the inferior petrosal sinus 

 and through a plexus of veins on the internal carotid artery; with the pterygoid 

 plexus through the foramen ovale, and with the angular vein through the ophthal- 

 mic vein. The two sinuses also communicate with each other by means of the 

 circular sinus. 



