BKANCHES OF THE EXTEKNAL CAEOTID AETEEY. 891 



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passes posterior to the lower part of the carotid artery in the neck to reach its 

 medial side, and the oesophagus has a less intimate relation with the right than 

 with the left common carotid artery. 



ARTERIA CAROTIS EXTERNA. 



The external carotid artery (Figs. 759, 760) is the smaller of the two terminal 

 branches of the common carotid ; its length is about 62 mm. (2J inches). It 

 extends from the upper border of the thyreoid cartilage to the back of the neck 

 of the mandible, where it terminates by dividing into the superficial temporal 

 and the internal maxillary arteries. 



Course. It commences in the carotid triangle, passes upwards, medial to the 

 posterior belly of the digastric and the stylo-hyoid muscles and the lower part of 

 the postero-medial surface of the parotid gland, then it enters a groove in the 

 medial border of the gland, through which it passes to the upper part of the 

 antero-medial surface posterior to the neck of the mandible, where it terminates. 



At its commencement it lies somewhat anterior and medial to the internal 

 carotid artery, but it inclines posteriorly as it ascends, and thus becomes superficial 

 to the internal carotid. Its course is indicated by a line drawn from the lobule of 

 the ear to the posterior extremity of the greater cornu of the hyoid bone. 



Relations. Posterior. In the lower part of its extent it is in close relation with the 

 internal carotid, and in the upper part of its course with the antero-medial surface of the 

 parotid gland. 



Medial. At its commencement the fibres of the inferior constrictor muscle are in con- 

 tact with its medial side, but at a higher level the structures which intervene between it 

 and the internal carotid viz., the stylo-pharyngeus muscle, the tip of the styloid process, 

 the stylo-glossus muscle, the glosso-pharyngeal nerve, and the pharyngeal branch of the 

 vagus separate it from the wall of the pharynx ; whilst medial both to it and to the 

 internal carotid artery are the external and internal laryngeal branches of the superior 

 laryngeal nerve. 



Superficial. In the carotid triangle it is overlapped by the anterior border of the 

 sterno-mastoid, and it is crossed, immediately below the level of its occipital branch, by 

 the hypoglossal nerve. It is also crossed by the lingual and common facial veins, and some- 

 times by the superior thyreoid vein also. At the level of the angle of the mandible it 

 passes under cover'of the posterior belly of the digastric and the stylo-hyoid muscles, which 

 separate it from the medial surface of the internal pterygoid muscle. As it emerges from 

 under cover of the stylo-hyoid it enters a groove in the parotid gland, and as it lies in 

 the gland the posterior facial vein (temporo-maxillary) descends superficial to the artery 

 and both the artery and the vein are crossed, superficially, by the branches of the facial 

 nerve. 



Branches. -Eight branches arise from the external carotid artery; of these, three the 

 superior thyreoid, the lingual, and the external maxillary spring from its anterior aspect 

 in the carotid triangle ; two arise from its posterior aspect, viz., the occipital and the 

 posterior auricular, the former commencing below the posterior belly of the digastric and 

 the latter above it ; one from its medial side, viz., the ascending pharyngeal, which arises 

 in the carotid triangle ; and two from its termination, viz., the superficial temporal and 

 the internal maxillary. 



BRANCHES OF THE EXTERNAL CAROTID ARTERY. 



(1) Arteria Thyreoidea Superior. The superior thyreoid artery (Figs. 759 

 and 761) springs from the anterior aspect of the lower part of the external carotid 

 artery, just below the tip of the greater cornu of the hyoid bone, and it terminates at 

 the upper extremity of the corresponding lobe of the thyreoid gland by dividing 

 into terminal branches. 



Course. From its commencement, in the carotid triangle, the artery runs 

 downwards and forwards to its termination. 



Relations. Medially it is in relation with the inferior constrictor muscle and the 

 jxternal laryngeal branch of the superior laryngeal nerve. 



Superficially it is covered, at its origin, by the anterior border of the sterno-mastoid 



