THE EXTERNAL CAROTID ARTERY 547 



interpeduncular space of the base of the brain by the union of the anterior cere- 

 bral arteries in front, by the diverging posterior cerebral arteries behind, and 

 is completed laterally by the junction of the latter with the posterior communi- 

 cating arteries and by the internal carotid. It is irregularly polygonal in out- 

 line. 



The ccrcliral arteries are very variable in arrangement, and the foregoino; aeeount is a brief 

 statement of the more usual disposition of the larger vessels. The internal cai'otid ai'tery often 

 arises with the occipital by a common trunk of variable length. 



THE EXTERNAL CAROTID ARTERY (Figs. 436, 437) 



This artery (A. carotis externa) by its size and direction constitutes the con- 

 tinuation of the common carotid. It passes forward on the lateral wall of the 

 pharynx at the lower border of the guttural pouch, covered by the submaxillary 

 gland and the stylo-maxillaris, digastricus, and stylo-hyoideus muscles. It then 

 emerges between the stylo-hyoideus and the great cornu of the hyoid bone, passes 

 upward on the latter parallel with the posterior l:)or(ler of the lower jaw, and termin- 

 ates about two inches (ca. 5 cm.) below the temporo-maxillary articulation by divid- 

 ing into superficial temporal and internal maxillary branches. It is crossed deeply 

 near its origin by the sujierior laryngeal and jiharyngeal branches of the vagus 

 nerve. Just before its eni(>rgence its superficial face is crossed by the hypoglossal 

 nerve, and the glosso-pharyngeal nerve passes over its inner surface at the ventral 

 border of the great cornu. The chi(>f collateral branches are the masseteric, ex- 

 ternal maxillary, and posterior aiu'icidar. It also furnishes variable branches to 

 the sul)maxillary and parotid glands, the guttural pouch, and the pharyngeal 

 lymph glands, as well as twigs to some adjacent muscles. 



1. The inferior masseteric or maxillo-muscular artery (A. masseterica inferior) 

 is given off from the external carotid at its emergence from beneath the stylo- 

 hyoideus. It passes downward and slightly forward unfler cover of the parotid 

 gland and over the tendon of insertion of the sterno-cephalicus to the posterior 

 border of the mandible and appears on the masseter muscle, into which it plunges 

 after a short course on its surface. It gives branches also to the internal pterygoid 

 and stylo-maxillaris muscles and the parotid gland. 



2. The external maxillary, facial, or submaxillary artery (A. maxillaris externa)^ 

 arises from the external carotid on the inner surface of the posterior belly of the di- 

 gastricus (Fig. 438). It runs downward and forward on the lateral wall of the 

 pharynx across the deep face of the stjdo-hyoideus toward the great cornu of 

 the hyoid bone, accompanied by the glosso-pharyngeal nerve in front and the hy- 

 poglossal nerve behind. After giving off the lingual artery at the posterior border 

 of the great cornu, it inclines more ventrally on the inner surface of the internal 

 pterygoid muscle, crosses over the hyo-glossus muscle, the hypoglossal nerve, the 

 submaxillary duct, and the intermediate tendon of the digastricus, and turns for- 

 ward in the submaxillary space. Here it lies on the lower part of the internal 

 pterygoid muscle, and is related internally to the submaxillary lymph glands, 

 above to the anterior belly of the digastricus, and below to the homonymous vein. 

 At the anterior border of the masseter it turns around the lower border of the jaw 

 and runs upward on the face in front of that muscle.^ At the turn the artery is 

 in front, the vein in the middle, and the parotid duct posterior. The artery and 

 vein pass upward along the anterior border of the masseter, under cover of the 

 facial ijanniculus and the zygomaticus, and are crossed superficially by branches 



^ By some authors the term facial is applied to the artery only after it turns around the lower 

 border of the jaw. 



^ The artery is conveniently placed at its inflection for taking the pulse, since it is super- 

 ficial and lies directly on the bone. 



