Iii6 A MANUAL OF ANATOMY 



panion vessel, but the temporo-maxillary vein descends in front of 

 it, in the parotid gland, to near the angle of the inferior maxilla, 

 beyond which point the artery has no vein. 



The course of the vessel may be indicated by a line drawn from 

 the side of the cricoid cartilage of the larynx to the tragus of the 

 auricle. 



Development. — The external carotid artery is the persistent part of the 

 ventral aorta above the level of the third arterial arch. 



Branches. — ^These are arranged in four sets, anterior, posterior, 

 ascending, and terminal, and are as follows ; 



Anterior. Posterior. Ascending. Terminal. 



Superior thjnroid. Occipital. Ascending Superficial temporal. 



Lingual. Posterior auricular, pharyng^il. Internal maxillary. 

 Facial. 



Superior Thyroid Artery. — ^This vessel arises in the carotid 

 triangle from the front part of the external carotid close to its 

 commencement. It takes an arched course forwards and down- 

 wards, passing under cover of the depressor muscles of the hyoid 

 bone. On reaching the apex of the lateral lobe of the thyroid 

 body it breaks up into its terminal branches, which enter the lobe 

 on its superficial aspect, and anastomose freely, within it, with 

 branches of the inferior thyroid artery, and, in the isthmus, with 

 its fellow of the opposite side. 



Branches. — ^These are £is follows ; 



Infrahyoid. Crico-tli5rroid. 



Stemo-cleido-mastoid. Glandular. 



Superior laryngeal. Muscular. 



The infrahyoid artery passes inwards on the thyro -hyoid 

 membrane, beneath the thyro -hyoid muscle, and close to the 

 lower border of the hyoid bone. It anastomoses at the middle 

 line with its fellow of the opposite side, and with the supra- 

 hyoid branch of the lingual artery of the same side. The sierno- 

 cleido -mastoid artery passes obliquely downwards and outwards, 

 over the upper part of the carotid sheath, to enter the deep surface 

 of the muscle from which it takes its name. It is liable to be cut 

 in ligation of the common carotid artery. The superior laryngeal 

 artery accompanies the internal laryngeal nerve, and passing 

 beneath the outer border of the thyro-hyoid muscle, it pierces the 

 thyro-hyoid membrane, to be distributed to the interior of the 

 lar57nx. The crico-thyroid artery passes transversely inwards upon 

 the crico-thyroid membrane, and anastomoses with its fellow of 

 the opposite side to form the crico-thyroid arch. This arch is 

 situated midway between the cricoid and thyroid cartilages, but, 

 notwithstanding this position, it may be in danger in the operation 

 of laryngotomy. The glandular branches are distributed to the 

 lateral lobe of the thyroid body. They anastomose freely with 



