THE MENINGES OF THE BRAIN. 



constitute the circular sinus (s. circular is) (Fig. 3). From the 

 bifurcation of the cavernous sinus^at the apex of the petrous bone, 

 the petrosal sinuses run outward along the corresponding superior 

 and inferior borders of that boneJj^Thejsuperior petrosal sinus 



Fig. 2. Horizontal section of skull, showing tentorium cerebelli, tentorial notch 

 and sinuses. (After Morris's Anatomy.) 



a. Infundibulum. b. Internal carotid artery, c. Optic tract, d. Third nerve, e. Basis 

 pedunculi. f. Cerebral aqueduct (Sylvii). g. Quadrigeminal body. h. Falx cerebri. 

 i. Tentorium cerebelli. j. Straight sinus, k. Crista galli. 1. Optic nerve, m. Spheno-' 

 parietal sinus, n. Middle cerebral artery, o. Anterior cerebral artery, p. Posterior com- 

 municating artery, q. Cavernous sinus, r. Superior cerebellar artery, s. Posterior cerebral 

 artery, t. Superior petrosal sinus, u. Free border of tentorium bounding tentorial notch. 

 v. Transverse sinus, w. Superior sagittal sinus. 



(Figs, i and 2) empties into the transverse sinus at the base of 

 the petrous bone; the inferior petrosal sinus, in its course to the 

 jugular foramen, is joined to its fellow, across the basilar process 

 of the occipital bone, by the basilar plexus (p. basilaris] and, in 



