CRANIAL CAVITY. 



calcarine fissure; parieto-occipital, running in the parieto- 

 occipital fissure. [820] 



Circle of Willis. This is an irregularly polygonal arterial 

 anastomosis at the base of the brain formed by the anterior 

 communicating, anterior cerebral, posterior communicating, 

 and posterior cerebral arteries. [821] 



VEINS. 



Unpaired Sinuses. The superior longitudinal begins at the 

 crista galli, runs in the attached margin of the falx cerebri and, 

 diverging slightly to the right (or left), becomes the right (or 

 left) lateral sinus at the level of the internal occipital protu- 

 berance; a dilatation (torcula Herophili) at its end is con- 

 nected with a similar dilatation of the straight and opposite 

 lateral sinuses. The inferior longitudinal occupies the posterior 

 two-thirds of the free margin of the falx cerebri and joins the 

 vena magna Galeni behind, forming the straight sinus. The 

 straight sinus occupies the attachment of the falx cerebri to the 

 tentorium and joins the left (or right) lateral sinus. The cir- 

 cular sinus surrounds the pituitary body and is usually formed 

 by two channels connecting the cavernous sinuses. The ba- 

 silar is a plexus, on the basilar part of the occipital, connect- 

 ing the cavernous, or inferior petrosal sinuses. [883] 



Paired Sinuses. Lateral: Each runs in a groove, outward 

 in the outer border of the tentorium to the posterior inferior 

 angle of the parietal, then downward on the mastoid, and for- 

 ward across the jugular process to join the internal jugular in 

 the jugular foramen. Occipital: Each runs in the lower at- 

 tached border of the falx cerebelli, to the lateral sinus of the 

 same side, or (uniting) either lateral sinus. Cavernous : Each 

 begins at the sphenoidal fissure, runs alongside the body of the 

 sphenoid, and divides, at the apex of the petrous bone, into 

 the superior and inferior petrosal. Superior petrosal: Each 

 runs from the cavernous to the lateral sinus in the attached 

 margin of the tentorium, along a groove on the petrous bone. 

 4 [491 



