Fig- IS- Base of skull with Arteries, Emerging Nerves and Sinuses 



of Dura Mater. 



The Brain has been cut away layer by layer to preserve the Basal Arteries in 

 position and as much as possible of the Nerves. The Spinal Cord, lias not 

 been cut at the level of the 2nd Cervical Nerve as usual, but the Bulb has been 

 divided through the Olivary Body. On the left side, the Tentorium has been 

 removed from the Apex of the Petrous Bone to the Torcular Herophili, the 

 Superior Petrosal and Lateral Sinuses being opened (the right middle meningeal 

 artery has been drawn double by mistake). 



The Venous Blood returning from the Brain runs into the Sinuses which 

 are found in the Dura Mater. The Blood from all the Sinuses eventually passes 

 into the Lateral Sinus and thence into the Internal Jugular Vein which commences 

 below the Jugular Foramen. 



The most important Sinuses are those which lie against the Skull and are 

 liable to be affected in injury or disease of the bone, especially the Superior 

 Longitudinal Sinus and the Lateral Sinus. Cf. Fig. i. As the Superior Longi- 

 tudinal Sinus usuall}' opens into the right Lateral Sinus, this Sinus and the Internal 

 Jugular Vein on the right side are usually larger than on the left. 



The Lateral Sinus extends from the Torcular Herophili, (or either side) 

 horizontally outwards (cf. Fig. 17) and then descends behind the Mastoid Process, 

 forming two curves towards the Jugular Foramen. In this last portion of its 

 course it gradually leaves the outer surface of the skull and is hardly liable to 

 injur)' from without. 



The course of the Cranial Nerves from the Brain to their foramina varies ; 

 in the Anterior and Middle Fossa the Nerves pass directly to their foramina; 

 but in the Middle Fossa the Vth Nerve runs under the Dura Mater for some 

 distance, when it forms the Gasserian Ganglion and divides into its 3 Divisions, 

 which again run separately under the Dura Mater to leave the SkuU by the 

 Sphenoidal Fissure, Foramen Rotundum and Foramen Ovale respectively. The 

 Ilird and IVth Nerves run in the outer wall of the Cavernous Sinus to the 

 Sphenoidal Fissure; the Internal Carotid Artery and the Vlth Nerve run in the 

 Cavernous Sinus. 



