= 
BLOOD SINUSES OF THE CRANIUM. 841 
The basilar sinus (plexus basilaris)—The term basilar sinus is applied to a 
venous plexus situated in the dura mater on the basilar part of the occipital bone. 
It connects the posterior ends of the cavernous or the anterior ends of the inferior 
petrosal sinuses together, and communicates below with the anterior spinal veins. 
The straight sinus (sinus rectus) is formed by the union of the inferior longi- 
tudinal sinus with the great vein of Galen. It runs downwards and backwards, 
along the line of attachment of the falx cerebri to the tentorium cerebelli. As a 
general rule it turns to the left at the internal occipital protuberance, dilates some- 
what, and becomes continuous with the left lateral sinus, its dilatation being united 
with the corresponding dilatation on the lower end of the superior longitudinal 
sinus—the toreular Herophili—by a transverse anastomosing channel. Oceasion- 
ally the straight sinus terminates in the right lateral sinus, ‘and in that case the 
superior longitudinal sinus ends in the left lateral sinus. It recelves some of the 
superlor cerebellar veins and a few tributaries from the falx cerebri. 
Paired Sinuses.—There are six pairs of sinuses—viz. the lateral, the occipital, 
the cavernous, the superior petrosal, the inferior petrosal, and the spheno- -parietal. 
Lateral Sinuses.—Each lateral sinus (sinus transversus) commences at the 
internal occipital protuberance, the right usually as the continuation of the superior 
longitudinal, and the left as the continuation of the straight sinus. Hach passes 
outwards in the outer border of the tentorium cerebelli and in a groove in the 
occipital bone. From the lateral angle of the occipital bone it passes on to the 
posterior inferior angle of the parietal bone, which it grooves; then it leaves the 
tentorium and turns downwards on the inner surface of the mastoid portion of the 
temporal bone; from the latter it passes to the upper surface of the jugular process 
of the occipital bone, and turns forwards and then downwards into the jugular 
foramen, where it becomes continuous with the internal jugular vein. 
Its tributaries are some of the superior and inferior cerebellar veins, a posterior 
diploic vein, and the superior petrosal sinus. It is connected with the veins out- 
side the cranium by emissary veins which pass through the mastoid and posterior 
condylar foramina. 
The occipital sinuses (sinus oecipitales) lie in the attached border of the falx 
cerebelli and in the dura mater along the postero-lateral boundaries of the foramen 
magnum ; frequently they unite above and open by a single channel into the com- 
mencement of either the right or the left lateral sinus, but their upper extremities 
may remain separate, and then each communicates with the commencement of the 
lateral sinus of its own side. They open below into the terminal part of the corre- 
sponding lateral sinuses, and they communicate with the posterior spinal veins. 
Kach occipital sinus is an anastomosing channel between the upper and lower 
extremities of the lateral sinus of the same side, and each receives a few inferior 
cerebellar veins. 
The cavernous sinuses lie at the sides of the body of the sphenoid bone. Each 
sinus (sinus cavernosus) commences anteriorly at the inner end of the sphenoidal 
fissure, where it receives the corresponding ophthalmic vein, and it terminates at 
the apex of the petrous portion of the temporal bone by dividing into the superior 
and the inferior petrosal sinuses. Its cavity, which is irregular in size and shape, 
is so divided by numerous fibrous strands that it assumes the appearance of 
cavernous tissue, and in its outer wall are embedded the internal carotid artery 
with its sympathetic plexuses, the third, fourth, first and second divisions of the 
fifth, and the sixth cranial nerves. Its tributaries are the spheno-parietal sinus 
and the inferior cerebral veins, including the superficial Sylvian vein. It com- 
municates with the opposite cavernous sinus by means of the circular sinus; with 
the pterygoid plexus in the zygomatic fossa by an emissary vein which passes 
either through the foramen ovale or through the foramen V esalii; with the internal 
jugular vein by small venous channels which accompany the internal carotid ar tery 
through the carotid canal, and by the inferior petrosal sinus; with the lateral 
sinus “by the superior petrosal sinus, and through the ophthalmic vein with the 
angular vein. 
“The spheno-parietal sinuses (s. spheno-parietales) are lodged in the dura mater 
on the under surfaces of the small wings of the sphenoid bone close to their posterior 
