n6 THE NERVOUS SYSTEM 



groups are brought into communication with the cavernous 

 sinus. 



Owing to its numerous communications, the cavernous 

 sinus may become the site of a septic thrombosis following 

 infective processes of the face, orbit, teeth or naso-pharynx. 

 The condition is usually accompanied by paralyses of the ocular 

 muscles and there may be sensory disturbances over the area 

 supplied by the ophthalmic nerve (Fig. 41). These com- 

 plications are due to the intimate relation which the third, 

 fourth, sixth and ophthalmic nerves bear to the cavernous 

 sinus, for, after they pierce the serous layer of the dura mater 

 and before they enter the orbit, they lie in the lateral wall of 

 the sinus, between the supporting dura mater and the lining 

 endothelium (Fig. 56). 



The Blood- supply of the Brain and its Membranes. 



The dura mater receives its blood-supply from the meningeal 

 arteries, which are placed between the endo-periosteum and 

 the serous layer. Of these the most important is the middle 

 meningeal artery. It arises from the internal maxillary artery, 

 which is one of the terminal branches of the external carotid, 

 and, entering the skull through the foramen spinosum, runs 

 forwards and laterally over the floor of the middle cranial fossa. 

 Its anterior branch runs upwards towards the vertex along 

 a line which may be said to correspond to the pre-central 

 sulcus (Fig. 3), and, when it is torn, the resulting blood- 

 clot exercises pressure on the neighbouring anterior central 

 gyrus (p. 5). The area involved and, consequently, the 

 symptoms will depend on the site of the clot, but, owing 

 to their position, the motor centres for the lower limb 

 (p. 5) are never affected in the first instance. Unless 

 the dura mater is ruptured, the haemorrhage is extra-dural in 

 position. 



The posterior branch of the middle meningeal artery runs 

 backwards along a line which lies a little above the level of 

 the middle temporal sulcus. Rupture of this division will not, 



