296 HEAD AND NECK 



nerve, and the styloid process or the stylo-hyoid ligament. 

 These structures lie to its medial side after they have passed 

 obliquely between it and the internal carotid, which has 

 gradually attained a plane posterior and medial to that in 

 which the external carotid lies. 



In the whole of its extent the external carotid is accom- 

 panied by numerous sympathetic nerve fibres, derived from 

 the upper cervical sympathetic ganglion ; they constitute the 

 external carotid plexus, which distributes offsets along all the 

 branches of the artery. 



Branches. The branches of the external carotid artery are 

 the superior thyreoid, the lingual, and the external maxillary 

 from its anterior aspect ; the occipital and the posterior 

 auricular from its posterior aspect ; the ascending pharyngeal 

 from its medial side ; and the superficial temporal and the 

 internal maxillary are its terminal branches. 



Arteria Thyreoidea Superior. This vessel arises within 

 the carotid triangle, from the anterior aspect of the external 

 carotid close to its origin. It runs downwards and anteriorly, 

 under cover of the omo-hyoid, sterno-hyoid, and sterno-thyreoid 

 muscles, to the apex of the lateral lobe of the thyreoid gland, 

 where it ends by breaking up into three terminal branches. 



The following branches proceed from it : 



Hyoid. 

 2. Superior laryngeal. 



4. Crico-thyreoid. 



5. Glandular. 



3. Sterno-mastoid. 



Ramus Hyoideus. This is a minute twig, which springs 

 from the superior thyreoid in the carotid triangle. It runs 

 along the lower border of the hyoid bone, under cover of the 

 thyreo-hyoid muscle, and anastomoses with its fellow of the 

 opposite side, and with the hyoid branch of the lingual 

 artery. 



Arteria Laryngea Superior. This is a larger vessel. It 

 springs from the superior thyreoid in the carotid triangle, 

 and, associating itself with the internal laryngeal nerve, it 

 enters the pharynx after piercing the thyreo-hyoid mem- 

 brane. 



Arteria Sternocleidomastoidea. The sterno-mastoid branch 

 is a small vessel which runs downwards and posteriorly, across 

 the carotid sheath along the upper border of the anterior 

 belly of the omo-hyoid muscle, to reach the deep surface of 

 the sterno-mastoid muscle, into which it sinks. It gives, 



