VENOUS SINUS OF THE DURA MATER 



649 



2. THE VENOUS SINUSES OF THE DURA MATER 



The venous sinuses of the dura mater [sinus durae matris] are endothelially 

 lined blood-spaces, situated between the periosteal and meningeal layers of the 

 dura mater. They are the channels by which the blood is conveyed from the 

 cerebral veins, and from some of the veins of the meninges and diploe, into the 

 veins of the neck. The sinuses at the base of the skull also carry the chief part of 

 the blood from the orbit and eyeball to the jugular veins. At certain spots the 

 sinuses communicate with the superficial veins by small vessels known as the emis- 

 sary veins, which run through foramina in the cranial bones. 



The venous sinuses are sixteen in number, six being median and unpaired, the 

 remaining ten consisting of five lateral pairs. The median sinuses are: — (1) the 

 superior sagittal; (2) the inferior sagittal; (3) the straight; (4) the occipital; (5) 

 the circular; and (6) the basilar plexus. The lateral and paired sinuses are: — 

 (7) the two transverse; (8) the two superior petrosal; (9) the two inferior petro- 

 sal; (10) the two cavernous; and (11) the two spheno-parietal. Occasionally 

 there are two additional sinuses, the two petro-squamous. 



(1) The superior sagittal (or longitudinal) sinus [sinus sagittalis superior] (fig. 

 515) lies in the median groove on the inner surface of the cranium along the 

 attached margin of the falx cerebri. It extends from the foramen caecum to the 



Fig. 513. — The Veins op the Diploe. 



(^FroTl. a spef^imen in St,. Rfl.rthnlnmfiw's Hnspital Musftvun.) 



The coronal 

 suture 



The lamboid 

 suture 



The occipital 

 diploic vein 



The posterior 

 temporal diploic 

 vein 



The mastoid 

 foramen 



internal occipital protuberance. It grooves from before backward the frontal 

 bone, the contiguous sagittal margins of the parietal bones, and the squamous por- 

 tion of the occipital bone In the foetus, and occasionally in the adult, it commu- 

 nicates (through the foramen caecum) with the nasal veins. It communicates 

 throughout life with each superficial temporal vein by means of a parietal emis- 

 sary vein [emissarium parietale] which passes through the parietal fora- 

 man. It is triangular on section, the base of the triangle corresponding to the 

 bone. Crossing it are a number of fibrous bands known as the chords of Willis, 

 and projecting into it in places are the arachnoidal (Pacchionian) granulations. 

 The parts of the sinus into which the arachnoidal granulations project are irregu- 

 lar lateral diverticula from the main channel known as the laamce laterales ffig. 

 517). In front the sinus is quite small, but it increases greatly in calibre as it 

 runs backward. It receives at intervals the superior cortical cerebral veins and 

 the veins from the falx. The former, for the most part, open into it in the direc- 

 tion opposite to that in which the blood is flowing in the sinus. They pass for 

 some distance in the walls of the sinus before opening into it. Posteriorly, at the 

 internal occipital protuberance, the superior sagittal sinus usually turns sharply to 



