THE HEAD AND NECK 1203 



lies along the back part of the lower border of the external pterygoid 

 muscle, crossing in front of the inferior dental nerve. The second, 

 or pterygoid, part usually lies upon the lower head of the external 

 pterygoid, and under cover of the insertion of the temporal muscle. 

 Its course through the zygomatic fossa is upwards and forwards, 

 and it sinks between the two heads of the external pterygoid on its 

 way to the pterygo-maxillary fissure. In many cases, however, 

 the second part of the vessel passes beneath the lower head of the 

 external pterygoid, crossing in front of the internal pterygoid 

 muscle and lingual nerve. Under these circumstances it forms a 

 projecting curve between the two heads of the external pterygoid 

 beneath the long buccal nerve. The third, or spheno-maxillary, 

 part is situated in the spheno-maxillary fossa, which it enters by 

 passing through the pterygo-maxillary fissure. In this fossa the 

 vessel and its branches are intimately related to the superior maxil- 

 lary nerve and Meckel's ganglion, with its branches. 

 Branches. — ^These are as follows : 



First Part. 



Deep auricular. 

 Tympanic. 

 Middle meningeal, 



giving ofE small 



meningeal. 

 Inferior dental. 



Second Part. 



Masseteric. 

 Internal pterygoid. 

 External pterygoid. 

 Posterior deep temporal. 

 Anterior deep temporal. 

 Buccal. 



Third Part 



Posterior dental. 



Infra-orbital. 



Descending palatine. 



Vidian. 



Pterygo-palatine. 



Spheno-palatine. 



Branches of the First Part. — ^The deep auricular artery, of small 

 size, ascends within the parotid gland, just behind the temporo- 

 mandibular joint, and pierces the anterior cartilaginous wall of the 

 meatus auditorius extemus. It supplies the cutaneous lining of 

 that passage, and the outer surface of the membrana tympani. 



The tympanic artery may be associated with the preceding at 

 its origin. It ascends beneath the external pterygoid, and enters 

 the t5mipanic cavity by passing through the fissure of Glaser. It 

 is distributed to the structures within the tympanum, and to the 

 inner surface of the membrana tympani. Around the circum- 

 ference of that membrane it forms an arterial ring with an offset 

 of the stylo-mastoid artery, which is a branch of the posterior 

 auricular. 



The middle meningeal artery, of large size, ascends beneath the 

 external pterygoid muscle, and, passing between the two roots of 

 origin of the auriculo-temporaJ nerve, it enters the cranial cavity 

 through the foramen' spino sum in the sphenoid bone. It then 

 passes upwards and forwards to the inner aspect of the antero- 

 inferior angle of the parietal bone, where it divides into two branches, 

 anterior and posterior, which ramify in the branching grooves on 

 the inner surface of the parietal bone. The artery is accompanied 

 by a plexus of sympathetic nerves, and by two veins. For the 

 distribution of the vessel within the cranium, see Index. Before 

 disappearing through the foramen spinosum the middle meningeal 



