BRANCHES OF THE EXTERNAL CAROTID ARTERY. 159 
(62 mm.). It extends from the upper border of the thyroid 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 beneath the 
posterior belly of the digastric and the stylo-hyoid muscles to enter the posterior 
part of the submaxillary triangle, where it disappears beneath the lower part of the 
parotid gland, and it terminates under cover, or in the substance of the upper part 
of the gland. 
At its commencement it lies somewhat in front of and to the inner side of the 
internal carotid artery, but, inclining slightly backwards as it ascends, it becomes 
superficial to the latter vessel, and its course is indicated by a line drawn from the 
lobule of the ear to the posterior extremity of the great cornu of the hyoid bone. 
Relations.—Posterior.—tIn 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 cartilaginous portion of the 
external auditory meatus. 
Lateral.—At its commencement the fibres of the inferior constrictor muscle are in con- 
tact with its inner 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 internal 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 the lingual, ranine, common facial, and superior 
thyroid veins are superficial to it, and the hypoglossal nerve crosses the artery immediately 
below the origin of its occipital branch. On the boundary line between the carotid and 
the submaxillary triangles the posterior belly of the digastric and the stylo-hyoid muscles 
cover the artery, and from the tip of the mastoid process downwards it is overlapped by 
the anterior border of the sterno-mastoid muscle. Above the posterior belly of the 
digastric the parotid gland is superficial to the artery, while still more superficially are 
the superficial fascia and the skin. In the substance of the parotid gland the temporo- 
maxillary vein descends on the outer side of the artery, and the facial nerve crosses on 
the outer side of the vein at a right angle to it. 
Branches.—Fight branches arise from the external carotid artery ; of these three spring 
from its anterior aspect, viz. the superior thyroid, the lingual, and the facial, all of which 
arise in the carotid triangle; two 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 inner side, viz. the ascending pharyngeal, which rises in the 
carotid triangle; and two from its termination, viz. the superficial temporal and the 
internal maxillary. 
BRANCHES OF THE EXTERNAL CAROTID ARTERY. 
(1) Superior Thyroid Artery (a. thyroidea superior, Figs. 554 and 556).—This 
vessel springs from the front of the lower part of the external carotid artery, just 
below the tip of the great cornu of the hyoid bone, and terminates at the upper ex- 
tremity of the lateral lobe of the thyroid body by dividing into its terminal branches. 
Course.—From its commencement in the carotid triangle the artery runs at 
first forwards and a little upwards, it then turns downwards to its termination. 
Relations.—/nternally it is in relation with the inferior constrictor muscle and the 
external laryngeal branch of the superior laryngeal nerve. 
Superficially it is covered at its origin by the anterior border of the sterno-mastoid ; 
afterwards, for a short distance, by fascia, platysma, and skin, and in the lower part of its 
extent by the omo-hyoid, the sterno-hyoid, and the sterno-thyroid muscles, and it is over- 
lapped by an accompanying vein. 
Branches.—(1) Zn the carotid triangle (a) an infra-hyoid branch (ramus hyoideus) 
runs along the lower border of the great cornu of the hyoid bone, under cover of the 
thyro-hyoid muscle, to anastomose with its fellow of the opposite side and with the supra- 
hyoid branch of the lingual artery. It supplies the thyro-hyoid muscle and membrane. 
(6) A laryngeal branch (a. laryngea superior) runs forwards beneath the thyro-hyoid 
muscle. It pierces the thyro-hyoid membrane in company with the internal laryngeal 
nerve, supplies the muscles, ligaments, and mucous membrane of the larynx, and 
