552 



ANGIOLOGY 



origin, this artery is more superficial, and placed nearer the middle line than the 

 internal carotid, and is contained within the carotid triangle. 



Relations. The external carotid artery is covered by the skin, superficial fascia, Platysma, 

 deep fascia, and anterior margin of the Sternocleidomastoideus; it is crossed by the hypoglossal 

 nerve, by the lingual, ranine, common facial, and superior thyroid veins; and by the Digastricus 

 and Stylohyoideus; higher up it passes deeply into the substance of the parotid gland, where 

 it lies deep to the facial nerve and the junction of the temporal and internal maxillary veins. 

 Medial to it are the hyoid bone, the wall of the pharynx, the superior laryngeal nerve, and a 

 portion of the parotid gland. Lateral to it, in the lower part of its course, is the internal carotid 

 artery. Posterior to it, near its origin, is the superior laryngeal nerve; and higher up, it is sepa- 

 rated from the internal carotid by the Styloglossus and Stylopharyngeus, the glossopharyngeal 

 nerve, the pharyngeal branch of the vagus, and part of the parotid gland. 



Branches. The branches of the external carotid artery may be divided into four 

 sets. 





Anterior. 



Superior Thyroid. 

 Lingual. 

 External Maxillary. 



Posterior. 

 Occipital. 

 Posterior Auricular. 



Ascending. 

 Ascending 

 Pharyngeal. 



Terminal. 



Superficial Temporal. 

 Internal Maxillary. 



1. The superior thyroid artery (a. thyreoidea superior} (Fig. 507) arises from 

 the external carotid artery just below the level of the greater cornu of the hyoid 

 bone and ends in the thyroid gland. 



Relations. From its origin under the anterior border of the Sternocleidomastoideus it runs 

 upward and forward for a short distance in the carotid triangle, where it is covered by the skin, 

 Platysma, and fascia; it then arches downward beneath the Omohyoideus, Sternohyoideus, and 

 Sternothyreoideus. To its medial side are the Constrictor pharyngis inferior and the external 

 branch of the superior laryngeal nerve. 



Branches. It distributes twigs to the adjacent muscles, and numerous branches 

 to the thyroid gland, anastomosing with its fellow of the opposite side, and with 

 the inferior thyroid arteries. The branches to the gland are generally two in 

 number; one, the larger, supplies principally the anterior surface; on the isthmus 

 of the gland it anastomoses with the corresponding artery of the opposite side: 

 a second branch descends on the posterior surface of the gland and anastomoses 

 with the inferior thyroid artery. 



Besides the arteries distributed to the muscles and to the thyroid gland, the 

 branches of the superior thyroid are : 



Hyoid. 

 Sternocleidomastoid . 



Superior Laryngeal. 

 Cricothyroid. 



The Hyoid Branch (ramus hyoideus; infrahyoid branch) is small and runs along 

 the lower border of the hyoid bone beneath the Thyreohyoideus and anastomoses 

 with the vessel of the opposite side. 



The Sternocleidomastoid Branch (ramus Sternocleidomastoideus; sternomastoid 

 branch) runs downward ancf lateralward across the sheath of the common carotid 

 artery, and supplies the Sternocleidomastoideus and neighboring muscles and 

 integument; it frequently arises as a separate branch from the external carotid. 



The Superior Laryngeal Artery (a. laryngea superior), larger than either of the 

 preceding, accompanies the internal laryngeal branch of the superior laryngeal 

 nerve, beneath the Thyreohyoideus; it pierces the hyothyroid membrane, and 

 supplies the muscles, mucous membrane, and glands of the larynx, anastomosing 

 with the branch from the opposite side. 



The Cricothyroid Branch (ramus cricothyreoideus) is small and runs transversely 

 across the Cricothyroid membrane, communicating with the artery of the opposite 

 side. 



