THE SINUSES OF THE DURA MATER. 



605 



tentorium. It is small arid narrow, arid connects together the cavernous and 

 lateral sinuses at each side. It receives some cerebellar and inferior cerebral veins, 

 and veins from the tympanic cavity. 



The Inferior petrosal sinus is situated in the groove formed by the junction of 

 the posterior border of the petrous portion of the temporal with the basilar process 

 of the occipital. It commences in front at the termination of the cavernous sinus, 

 and behind joins the lateral sinus after it has passed through the jugular foramen ; 

 the junction of these two sinuses forming the commencement of the internal jugu- 

 lar vein. The inferior petrosal sinus receives the veins from the internal ear and 

 also veins from the medulla, pons, and under surface of the cerebellum. 



The junction of the two sinuses takes place at the lower border of, or just 

 external to, the jugular foramen. The exact relation of the parts to one another 

 in the foramen is as follows: The inferior petrosal sinus is in front, with the 

 rneningeal branch of the ascending pharyngeal artery, and is directed obliquely 

 downward and backward : the lateral sinus is situated at the back part of the fora- 



Faljf. cerebri 



tlic nerve 



Int. carotid artery 



Motor oviili tte.n-e 



Inferior 

 petrosal siniw 



Dorxum xelltv 



9th. 10th, aiul llth 

 cranial nerve* 



Lateral sinus 

 FIG. 329. Relation of nerves to sinuses in jugular foramen. (Henle.) 



men with a meningeal branch of the occipital artery, and between the two are 

 the glosso-pharyngeal, pneumogastric, and spinal accessory nerves. These three 

 sets of structures are divided from each other by two processes of fibrous tissue. 

 The junction of the sinuses takes place superficial to the nerves, so that these latter 

 lie a little internal to the venous channels in the foramen (see Fig. 329). These 

 sinuses are semicylindrical in form. 



The Transverse Sinus, or basilar sinus, consists of several interlacing veins 

 between the layers of the dura mater over the basilar process of the occipital bone, 

 which serve to connect the two inferior petrosal sinuses. With them the anterior 

 spinal veins communicate. 



Emissary Veins. The emissary veins are vessels which pass through apertures 



