THE ARACHNOID. 



277 



processes of the sphenoid. Attached along the median 

 line of its superior surface, nearly at right angles, is the 

 falx cerebri. The inferior surface of the tentorium is 

 concave, and gives attachment to the falx cerebelli, which 

 corresponds to the falx cerebri, but which is compara- 

 tively slightly developed. The dura mater also sends 

 tubular prolongations or sheaths around the filaments 



FIG. 119. THE SINUSES OP THE DURA MATER. 



1, superior longitudinal sinus; 2. inferior longitudinal sinus; 3, straight sinus, deriv- 

 ing blood from 1 and also from the veins of Galen (11) ; Nos. 1. 2, and 3 bound the falx 

 cerebri : 4, the torcular Herophili, where four sinuses meet ; 5, lateral sinus ; 6, superior 

 petrosal sinus, joining the lateral sinus (5) with the cavernous sinus (8) ; 7, inferior petro- 

 sal sinus, joining the cavernous sinus (8) with the jugular vein (9) ; 8, cavernous sinus; 

 9. internal jugular vein formed by two sinuses (5 and 7); 10, occipital sinus ; 11, venae 

 Galeni ; 12, vein passing to nasal cavity ; 13, foramen caecum. 



of the olfactory, optic, ophthalmic division of the fifth 

 nerves as they pass out of the skull. On the surface of 

 the dura mater are a number of fibrous, split-pea-shaped 

 bodies called the Pacchionian bodies. Arteries are freely 

 distributed to the dura mater. 



THE ARACHNOID. 



The arachnoid is a serous sac consisting of two layers, 

 visceral and parietal. The parietal layer lines the inner 



