THE SINUSES OF THE DURA 



725 



sinus to the lateral sinus of the opposite side to that into which the sap-ittal sinus 

 is prolonged. Its terminal part communicates by a cross-branch with the torcular 

 Herophili (confluence of the sinuses}. Besides the inferior sagittal sinus, it receives 

 the vena magna Galeni and the superior cerebellar veins. A few transverse bands 

 cross its lumen. 



The lateral sinuses (Figs. 502 and 503) are of large size and commence at the 

 internal occipital protuberance; one, generally the right, being the direct continua- 

 tion of the superior sagittal sinus, the other of the straight sinus' Each lateral 

 sinus (sinus transversus, BNA) passes outward and forward, describing a slight 

 curve with its convexity upward, to the base of the petrous portion of the tem- 

 j>oral bone, and is situated, in this part of its course, in the attached margin of the 



MCNINQEAL 

 VEIN 



SUPERIOR 

 SAGITTAL 

 SINUS 



PARASINOIDAL 

 SINUS 



FIG 504. Sagittal sinus seen from above after removal of the skullcap. The chordae Willisii are clearly 

 visible. The parasinoidal sinuses are also well shown. Probes passing from the latter to the longitudinal 

 sinus show that they communicate. (Poirier and Charpy.) 



tentorium cerebelli; it then leaves the tentorium, curves downward and inward 

 to reach the jugular foramen, where it terminates in the internal jugular vein. 

 In its course it rests upon the inner surface of the occipital, the postero-inferior 

 angle of the parietal , the mastoid portion of the temporal bone, and on the occipital 

 again, at the jugular process, just before its termination. The portion of the sinus 

 which occupies the groove on the mastoid portion of the temporal bone is known 

 as the sigmoid sinus. The lateral sinuses are frequently of unequal size, that 

 formed by the sagittal sinus being the larger, and they increase in size as they 

 proceed from behind forward. The horizontal portion is triangular on section, 

 the curved portion semicylindric. Their inner surface is smooth, and not crossed 

 by the fibrous bands found in the other sinuses. The lateral sinuses receive 

 the blood from the superior petrosal sinuses at the base of the petrous portion of 



