n8 HEAD AND NECK 



Then it runs forwards, in the cavernous sinus, to the medial 

 side of the anterior clinoid process, where it turns upwards, 

 pierces the inner layer of the dura mater and the arachnoid, 

 and gives off its ophthalmic branch, which runs forwards 

 below the optic nerve into the orbit. The artery was cut 

 immediately behind its ophthalmic branch during the early 

 stages of the removal of the brain (Pigs. 36, 39). 



Meningeal Arteries. The meningeal arteries are the 

 nutrient arteries of the dura mater, and of the inner table 

 and diploe of the cranial bones. They are derived from a 

 great number of different sources, but the only one of any 

 size is the middle meningeal branch of the internal maxillary 

 artery. The others are small twigs, and, except in a well- 

 injected subject, will not be easily made out. They are : 

 (i) anterior meningeal^ from the anterior ethmoidal artery; (2) 

 a meningeal branch of the lacrimal artery ; (3) the accessory 

 meningeal) from the internal maxillary artery; (4) some small 

 branches from the ascending pharyngeal, occipital, and ver- 

 tebral arteries. 



Each middle meningeal artery is a branch of the corre- 

 sponding internal maxillary artery. It enters the cranium 

 through the foramen spinosum of the sphenoid bone, and 

 divides, upon the inner surface of the great wing of that bone, 

 into two large terminal branches. The anterior of the two 

 branches ascends upon the great wing of the sphenoid, and 

 upon the anterior inferior angle of the parietal bone, grooving 

 both deeply, whilst the posterior branch turns backwards and 

 upwards upon the squamous portion of the temporal bone. 

 The branches which proceed from the two main divisions 

 spread out widely and, with the accompanying venous 

 channels, occupy the arborescent grooves on the inner 

 surface of the cranial vault (Fig. 204). 



The vein which accompanies the middle meningeal artery 

 passes through the foramen spinosum and ends in the plexus 

 around the external pterygoid muscle. 



Each anterior meningeal artery proceeds from the anterior 

 ethmoidal artery as it accompanies the anterior ethmoidal 

 nerve across the cribriform plate of the ethmoid bone. 

 It supplies a limited area of dura mater and bone in the 

 anterior fossa of the cranium. 



The meningeal branch of the lacrimal artery enters the 

 middle cranial fossa through the superior orbital fissure, and 



