THE EXTERNAL CAEOTID ARTERY. 393 



the cerebral and ophthalmic branches of the internal carotid from the vertebral arteries and the 

 internal carotid of the opposite side, by means of the free communications existing between 

 these vessels in the circle of Willis. The branches of the external carotid receive blood from 

 the subclavian artery through the anastomoses of the superior and inferior thyroid arteries, 

 and of the occipital with the ascending cervical, vertebral, and deep cervical arteries, and from 

 the external carotid of the opposite side through the anastomoses of the two superior thyroid, 

 lingual, facial, superficial temporal, and occipital arteries. 



EXTERNAL CAEOTID ARTERY (II). 



POSITION AND RELATIONS. The external carotid artery, distributed mainly to 

 the face and to the walls of the cranium, is smaller than the internal in young 

 persons ; but the two are nearly of equal size in adults. It reaches from the point 

 of division of the common carotid, opposite or a little above the upper margin of 

 the thyroid cartilage, nearly to the neck of the lower jaw, where it divides into its 

 two terminal branches, the superficial temporal and the internal maxillary. It is 

 about 2 \ inches long, and diminishes rapidly as it ascends, owing to the number and 

 size of the branches which spring from it. 



At first the external carotid lies in front of and somewhat nearer the median 

 plane than the internal carotid ; but it soon becomes superficial to that artery, 

 inclining slightly backwards as it ascends to its place of division. In its lower part 

 the artery is covered by the platysrna myoides and the fascia, and in the natural con- 

 dition of the parts it is overlapped by the sterno-mastoid (cf. p. 391) ; in its upper 

 part it is deeply placed, passing first beneath the stylo-hyoid and digastric muscles, 

 and finally becoming embedded in the substance of the parotid gland. At its com- 

 mencement it is in contact with the pharynx and hyoid bone ; farther up it is 

 separated by a portion of the parotid gland from the back of the ramus of the lower 

 jaw and the stylo-maxillary ligament, and rests upon the styloid process and the 

 stylo-pharyngeus muscle, which, with the glosso-pharyngeal nerve, are interposed 

 between it and the internal carotid artery. 



Relatwn to veins. This artery has usually no companion vein, but in the parotid 

 gland the temporo-mamllary trunk is superficial to it, and the anterior division of 

 this, passing down to join the facial vein, is sometimes placed with the artery 

 beneath the digastric muscle ; below the digastric it is crossed by the facial and 

 lingual veins as they pass backwards to open into the internal jugular. 



Relation to nerves. Close to the lower border of the digastric muscle the external 

 carotid artery is crossed by the hypoglossal nerve, and at a short distance from its 

 upper end, in the substance of the parotid gland, by the facial nerve. The glosso- 

 pliaryngeal nerve lies between it and the internal carotid ; and the superior and 

 external laryngeal nerves are on the inner side of both vessels. 



BRANCHES. The branches of the external carotid artery are eight in number, 

 viz., three directed forwards, the superior thyroid, the lingual, and the facial ; two 

 directed backwards, the occipital and posterior auricular ; one on the inner side, the 

 ascending pharyngeal ; and the superficial temporal and internal maxillary, the 

 two terminal branches into which the trunk divides. 



In addition to the principal branches here enumerated, the external carotid gives 

 off small offsets to the parotid gland, and to the masseter and internal pterygoid 

 muscles. 



Varieties. The peculiarities in the origin of this vessel have been noticed along with the 

 varieties of the common carotid artery. Absence of the external carotid artery has been met 

 with in some rare cases, the several branches arising at intervals from a single trunk which 

 represented the common and internal carotids. The branches are not unfrequently crowded 

 together on the main stem, near the commencement, or at a higher point. Occasionally they 

 take origin at regular distances in the whole length of the vessel. The usual number of 

 branches may be diminished by the origin from another artery of one of the ordinary branches , 



