ANATOMY IN A NUTSHELL. 489 



The torcular Herophili is a dilatation at the point on the eight side of the 

 internal occipital protuberance where the superior Longitudinal, occipital and 

 straight sinuses meet. 



2. The inferior longitudinal sinus passes along the lower border of the 



falx cerebri. It receives veins from the falx cerebri and also some from the 

 sagittal surface of the hemispheres. It ends in the straight sinus, ami on cross 

 section is circular. This sinus, as well as the preceding one. increases in size 

 from before backward. 



3. The straight sinus connects the inferior longitudinal sinus with the 

 superior longitudinal sinus and is situated at the junction of the falx cerebri 

 with the tentorium cerebelli. The inferior longitudinal sinus, venae Galeni, 

 and superior cerebellar veins empty into it. 



4. and 5. The lateral sinuses are two in number and are situated where 

 the tentorium cerebelli joins the bone. The right one, after receiving the blood 

 from the superior longitudinal and occipital sinus, passes to the light as far as 

 the petrous portion of thetemporal bone. It then passes downward and in- 

 ward to the jugular foramen, where it receives the inferior petrosal sinus to 

 make the jugular vein. It also receives the superior petrosal sinus at the base 

 of the petrous portion of the temporal hone. The left lateral sinus has a sim- 

 ilar description but receives the blood from the straight sinus. It occasionally 

 receives the blood from the superior longitudinal and occipital sinus, and then 

 the right lateral sinus receives the blood from the straight sinus. 



6. and 7. The occipital sinus which is the smallest of these sinuses, may 

 be double. It is situated where the falx cerebelli joins the hone, ami as said 

 before, it empties into the torcular Herophili. 



These seven sinuses are situated on the upper and back part of the skull, 

 while the remaining sinuses of the dura mater are situated at the base of the 

 skull. 



8. and 9. The cavernous sinuses pass from the sphenoidal fissure to the 

 apex of the pelrous portion of the temporal hone. They are formed by the 

 ophthalmic vein and end by dividing into the superior and inferior petrosal 

 sinuses. In each cavernous sinus the following structures are found; (a) The 

 third cranial nerve, (b) the fourth cranial nerve, (c) the ophthalmic division 

 of the fifth cranial, (e) the sixth cranial, (f) the internal carotid artery. For 

 position of these structures in this sinus see plate CCXXXII. The facial vein 

 communicates with this sinus through the ophthalmic vein. The circular >inm 

 connects the two cavernous sinuses. 



10. The circular sinus surrounds the hypophysis. The anterior segment 

 of this circle is larger than the posterior one. One or the other of these seg- 

 ments may be absent. 



11. and 12. The superior petrosal sinuses are two in number, one on 

 either side, and they connect the cavernous with the lateral sinus. They are 



situated along tin' superior border of the petrous portions of the temporal 

 bone. Veins fromtympanic cavity, some cerebellar vein- and inferior cerebral 

 Veins, pass into it . 



