404 THE ARTERIES OF THE HEAD AND NECK. 



parotid gland at its origin below the condyle of the jaw. It runs with a tortuous 

 course through the zygomatic fossa at the base of the skull, furnishing numerous 

 branches to the walls of the cranium and the deep parts of the face ; and for con- 

 venience of arrangement it is usually divided into three parts. 



In the first part the artery is directed nearly horizontally forwards beneath the 

 ramus of the jaw and along the lower border of the external pterygoid muscle, 

 having to its inner side the internal lateral ligament of the temporo-maxillary 

 articulation and the inferior dental nerve. It is accompanied by the internal 

 maxillary vein, and the auriculo-temporal nerve is above the vessels. The second 

 part courses obliquely upwards and forwards either on the outer or inner side of the 

 lower head of the external pterygoid, in the former case being covered by the 

 insertion of the temporal muscle ; while if occupying the deeper position the vessel 

 lies above the internal pterygoid muscle, crosses over the lingual nerve, and then 

 emerges with the buccal nerve (which is above the artery) through the interval 

 between the heads of the external pterygoid. In its third part the artery winds 

 inwards over the back of the superior maxilla to the spheno-maxillary fossa, where it 

 ends close to the spheno-palatine foramen, and just below the superior maxillary 

 nerve, by dividing into its terminal branches descending palatine, vidian, pterygo- 

 palatine and nasal. The second and third parts of the artery are thickly surrounded 

 by veins belonging to the pterygoid plexus. 



Branches. A. Of the first part. (a) The deep auricular branch, of small size, 

 and often arising in common with the next offset, perforates the anterior wall of 

 the external auditory meatus, and supplies the skin and outer part of the tympanic 

 membrane. 



(Z>) The tympanic branch, also small and variable in its origin, enters the 

 tympanum by the fissure of Glaser, and is distributed to the structures within that 

 cavity and the tympanic membrane, anastomosing with the stylo-mastoid artery (see 

 p. 401). 



(c) The middle or great meningeal artery (v), the largest branch of the internal 

 maxillary, passes directly upwards under cover of the external pterygoid muscle, 

 between the two roots of the auriculo-temporal nerve, and enters the skull by the 

 foramen spinosum of the sphenoid bone. Within the cranium, it ascends towards 

 the anterior inferior angle of the parietal bone, and divides into two branches, which 

 subdivide and ramify in deep arborescent grooves on the inner surface of the calvaria, 

 passing upwards on the parietal bone as high as the vertex, forwards to the frontal 

 bone, and backwards to the occipital bone. 



Immediately on entering the cranium the meningeal artery gives offsets to the 

 Grasserian ganglion and the surrounding dura mater, a small petrosal branch which 

 enters the hiatus Fallopii and anastomoses with the stylo-mastoid branch of the 

 posterior auricular artery, and minute tympanic twigs through the petro-squamous 

 fissure. Higher up an orlital branch passes from the trunk, or its anterior division, 

 to the outer end of the sphenoidal fissure, and communicates with the lachrymal 

 artery of the ophthalmic. 



(d) The small meningeal artery, usually arising from the preceding, ascends on 

 the inner side of the inferior maxillary nerve, and enters the skull through the 

 foramen ovale to supply the Gasserian ganglion and the dura mater in the middle 

 fossa. 



(<?) The inferior dental artery, passing downwards, enters the dental canal with 

 the inferior dental nerve, and subsequently escapes on the face by the mental fora- 

 men. As it enters the canal, it gives off the mylo-hyoid branch, which, with the 

 nerve bearing the same name, runs in a groove on the inner surface of the jaw, 

 below the dental foramen, and ramifies on the under surface of the mylo-hyoid 

 muscle. In its course through the bone, the inferior dental artery gives off small 



