passes posterior to the lower part of the carotid artery in the neck to reach its medial side, and the oesophagus has a less intimate relation with the right than with the left common carotid artery.

ARTERIA CAROTIS EXTERNA.

The external carotid artery (Figs. 759, 760) is the smaller of the two terminal branches of the common carotid; its length is about 62 mm. (2 inches). It extends from the upper border of the thyreoid 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, medial to the posterior belly of the digastric and the stylo-hyoid muscles and the lower part of the postero-medial surface of the parotid gland, then it enters a groove in the medial border of the gland, through which it passes to the upper part of the antero-medial surface posterior to the neck of the mandible, where it terminates.

At its commencement it lies somewhat anterior and medial to the internal carotid artery, but it inclines posteriorly as it ascends, and thus becomes superficial to the internal carotid. Its course is indicated by a line drawn from the lobule of the ear to the posterior extremity of the greater cornu of the hyoid bone.

Relations. Posterior.-In 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 antero-medial surface of the parotid gland.

Medial. At its commencement the fibres of the inferior constrictor muscle are in contact with its medial 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 medial 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 it is overlapped by the anterior border of the sterno-mastoid, and it is crossed, immediately below the level of its occipital branch, by the hypoglossal nerve. It is also crossed by the lingual and common facial veins, and sometimes by the superior thyreoid vein also. At the level of the angle of the mandible it passes under cover of the posterior belly of the digastric and the stylo-hyoid muscles, which separate it from the medial surface of the internal pterygoid muscle. As it emerges from under cover of the stylo-hyoid it enters a groove in the parotid gland, and as it lies in the gland the posterior facial vein (temporo-maxillary) descends superficial to the artery and both the artery and the vein are crossed, superficially, by the branches of the facial

nerve.

Branches. Eight branches arise from the external carotid artery; of these, three-the superior thyreoid, the lingual, and the external maxillary-spring from its anterior aspect in the carotid triangle; two arise 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 medial side, viz., the ascending pharyngeal, which arises in the carotid triangle; and two from its termination, viz., the superficial temporal and the internal maxillary.

BRANCHES OF THE EXTERNAL CAROTID ARTERY.

(1) Arteria Thyreoidea Superior.-The superior thyreoid artery (Figs. 759 and 761) springs from the anterior aspect of the lower part of the external carotid artery, just below the tip of the greater cornu of the hyoid bone, and it terminates at the upper extremity of the corresponding lobe of the thyreoid gland by dividing into terminal branches.

Course. From its commencement, in the carotid triangle, the artery runs downwards and forwards to its termination.

Relations.-Medially 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-thyreoid muscles, and it is overlapped by an accompanying vein.

Branches.-(1) In the carotid triangle―(a) A hyoid branch runs along the lower border of the greater cornu of the hyoid bone, under cover of the thyreo-hyoid muscle, to anastomose with its fellow of the opposite side and with the hyoid branch of the lingual artery. It supplies the thyreo-hyoid muscle and membrane.

(b) The superior laryngeal branch runs forwards, deep to the thyreo-hyoid muscle. It pierces the thyreoid hyo-membrane, in company with the internal laryngeal nerve, supplies the muscles, ligaments, and mucous membrane of the larynx, and anastomoses with its fellow of the opposite side, with branches of the crico-thyreoid artery, and with the terminal branches of the inferior thyreoid artery.

(c) The sternocleido-mastoid branch passes downwards and posteriorly, along the upper border of the anterior belly of the omo-hyoid muscle and across the common carotid artery, to the deep surface of the sterno-mastoid muscle. It anastomoses, in the sternomastoid, with branches of the occipital and transverse scapular arteries.

(2) In the muscular triangle-(d) A crico-thyreoid branch passes anteriorly, either superficial or deep to the sterno-thyreoid. It crosses the crico-thyreoid muscle to anastomose, in front of the crico-thyreoid ligament, with its fellow of the opposite side, and, by branches which perforate the crico-thyreoid ligament, with laryngeal branches of the superior and inferior thyreoid arteries. It supplies the adjacent muscles and membrane. (e) The terminal branches are anterior, medial, and lateral.

The anterior terminal branch descends along the anterior border of the corresponding lobe of the thyreoid gland, and the upper border of the thyreoid isthmus, to anastomose with its fellow of the opposite side. The medial branch is the largest; it is distributed to the medial surface of the lobe. The lateral branch, which ramifies in the lateral surface of the corresponding lobe, is the smallest. All three terminal branches supply glandular branches to the thyreoid gland. They anastomose with each other and with branches from the inferior thyreoid artery.

(2) Arteria Lingualis.-The lingual artery (Figs. 759 and 761) springs from the anterior aspect of the external carotid, opposite the tip of the greater cornu of the hyoid bone, and terminates, as the arteria profunda linguæ (O.T. ranine artery), which ends beneath the tip of the tongue, where it anastomoses with its fellow of the opposite side.

Course. Whilst in the carotid triangle, the first part of the artery forms a loop with the convexity upwards. The second part passes forwards, medial to the hyoglossus muscle, immediately above the greater cornu of the hyoid bone, to the anterior border of the hyo-glossus, where it gives off a sublingual branch and becomes the arteria profunda linguæ. The profunda linguæ artery passes obliquely forwards and upwards, under cover of the anterior border of the hyo-glossus, and then turns directly forwards on the under surface of the tongue to the tip, lying between the inferior lingualis laterally and the genio-glossus medially.

Relations. The first part of the lingual artery is crossed superficially by the hypoglossal nerve, and is covered by skin, fascia, and the platysma; it rests medially against the middle constrictor of the pharynx. The second part is deeper. It lies between the middle constrictor medially and the hyo-glossus laterally, and is separated by the latter from the hypoglossal nerve, the vena comitans hypoglossi, and the lower part of the submaxillary gland. The profunda artery of the tongue ascends almost vertically, parallel with and medial to the anterior fibres of the hyo-glossus, which are covered by the mylohyoid, and between the hyoglossus and the genio-glossus; then it runs forwards between the inferior lingualis and the genio-glossus muscles, and is covered, on its lower surface, by the mucous membrane of the tongue. Thus, at its termination, near the frenulum linguæ, it is comparatively superficial.

Branches. (a) The ramus hyoideus, a small branch which arises in the carotid triangle and runs along the upper border of the greater cornu of the hyoid bone. It anastomoses with its fellow of the opposite side and with the hyoid branch of the superior thyreoid artery.

(b) The dorsalis linguæ is a branch of moderate size which arises from the second part of the artery and is not uncommonly double. It ascends, between the hyo-glossus and the genio-glossus, to the dorsum of the tongue, where it branches and anastomoses with its fellow of the opposite side around the foramen cæcum. It supplies the posterior part of

the tongue as far back as the epiglottis, and sends branches, posteriorly, to the palatine tonsil which anastomose with the tonsillar twigs of the ascending palatine branch of the external maxillary and with the ascending pharyngeal artery.

(c) A sublingual branch arises at the lower part of the anterior border of the hyoglossus muscle and runs anteriorly and upwards, between the mylo-hyoid and the genioglossus, to the sublingual gland, which it supplies; it also supplies the mylo-hyoid, the genio-glossus, and the genio-hyoid muscles. It anastomoses with its fellow of the opposite side, with the arteria profunda by a branch which it sends along the frenulum linguæ, and, through the mylo-hyoid muscle, with the submental branch of the external maxillary.

(3) Arteria Maxillaris Externa (O.T. Facial). The external maxillary artery (Fig. 759) arises from the front of the external carotid, immediately above the lingual. It ends at the angle of the mouth, where it becomes the angular artery.

Course.-It commences in the carotid triangle, immediately above the lingual, and passes upwards to the angle of the mandible, on the lateral surface of the middle constrictor muscle. Still ascending, it lies between the posterior belly of the digastric and the stylo-hyoid muscles laterally, and the superior constrictor medially, and it is separated from the palatine tonsil by the superior constrictor. When it reaches the upper border of the stylo-hyoid it enters a groove in the posterior part of the submaxillary gland and runs downwards and anteriorly, between the lateral surface of the gland and the internal pterygoid muscle, to the posterior end of the lower border of the body of the mandible. There it pierces the deep cervical fascia, turns round the inferior border of the mandible, at the anterior border of the masseter, enters the face and continues upwards and forwards to its termination.

Relations. In the carotid triangle the artery is comparatively superficial, except just at its origin, which is overlapped by the anterior fibres of the sterno-mastoid muscle. As it ascends it is in relation, on the medial side, with the middle and superior constrictor muscles, and, as already stated, the superior constrictor separates it from the palatine tonsil. Its relations between the point where it passes medial to the posterior belly of the digastric and the point where it turns round the lower border of the mandible have been given in the description of its course.

After turning round the lower border of the body of the mandible, which it grooves slightly, the artery becomes more superficial than in any other part of its course, being covered only by platysma, fascia, and skin. At that point the anterior facial vein is immediately posterior to the artery, lying on the surface of the masseter. In the face the artery lies between the platysma, the risorius, the zygomaticus major, and the infraorbital section of the quadratus labii superioris (O.T. levator labii superioris), which, with skin and fascia, are superficial to it, and the buccinator and the musculus caninus (O.T. levator anguli oris), which are deeper. The termination of the artery is in the substance of the quadratus labii superioris.

The anterior facial vein, though still posterior to the artery in the face, runs a somewhat straighter course, and is situated at some little distance from it.

Branches.-Four named branches are given off in the neck, and several in the face. In the Neck. (a) The ascending palatine branch (Fig. 761) is a small artery which arises from the external maxillary under cover of the posterior belly of the digastric. It ascends, and, after passing between the stylo-glossus and the stylo-pharyngeus muscles, reaches the apex of the petrous portion of the temporal bone, where it turns downwards, accompanying the levator veli palatini muscle, pierces the pharyngeal aponeurosis, and enters the soft palate.

It supplies the lateral wall of the upper part of the pharynx, the soft palate, the palatine tonsil, and the auditory (O.T. Eustachian) tube, and it anastomoses with the tonsillar branch of the external maxillary, the dorsalis linguæ, the descending palatine branch of the internal maxillary, and with the ascending pharyngeal artery, which sometimes replaces it.

(b) The tonsillar branch, a small artery which arises close to the ascending palatine. It passes upwards between the internal pterygoid and the stylo-glossus, pierces the superior constrictor, and terminates in the palatine tonsil. It supplies the middle and superior constrictor muscles, and it anastomoses with the dorsalis linguæ, with the ascending palatine branch, and with the ascending pharyngeal artery.

(c) The submaxillary or glandular branch is frequently represented by two or three small twigs which pass directly into the submaxillary gland.

(d) The submental branch arises from the external maxillary just as the latter vessel turns round the inferior border of the mandible. It is the largest branch given off in the neck, and it runs forwards, on the lateral surface of the mylo-hyoid muscle, and medial to the upper part of the submaxillary gland, to the symphysis menti; there it turns upwards, round the margin of the mandible, and it terminates by anastomosing with branches of the mental and inferior labial arteries. In the neck the submental artery supplies the mylohyoid muscle, and the submaxillary and sublingual glands, the latter by a branch which perforates the mylo-hyoid muscle. It anastomoses with the mylo-hyoid branch of the inferior alveolar and with the sublingual artery. In the face it supplies the structures of the lower lip, and anastomoses with the mental branch of the inferior alveolar, and with the inferior labial branches of the external maxillary artery.

In the Face.-(e) The inferior labial branch (O.T. inferior coronary) arises from the front of the external maxillary artery below the level of the angle of the mouth. It runs medially, deep to the triangularis, the quadratus labii inferioris, and the orbicularis oris. In the substance of the lower lip it lies close to the mucous membrane and anastomoses, in the median plane, with its fellow of the opposite side.. It supplies the structures in its immediate neighbourhood.

(f) The superior labial (O.T. superior coronary) springs from the front of the external maxillary about the level of the angle of the mouth. It runs medially, between the orbicularis oris and the mucous membrane of the upper lip, to the median plane, supplying the skin, muscles, and mucous membrane of the upper lip, and, by a septal branch, the lower and anterior part of the septum of the nose. It anastomoses with its fellow of the opposite side, with the lateral nasal, and, on the septum nasi, with the septal branch of the spheno-palatine artery.

(g) The masseteric branch, sometimes represented by several twigs, arises from the posterior aspect of the facial trunk, a short distance above the lower margin of the mandible. It passes upwards and posteriorly, across the masseter, and anastomoses with the transverse facial artery.

(h) The buccal is an inconstant branch which, when present, arises from the posterior aspect of the external maxillary artery above the masseteric branch. It runs upwards and posteriorly, across the buccinator muscle, to anastomose with the buccinator branch of the internal maxillary artery.

(2) The lateral nasal springs from the external maxillary at the point where it becomes the angular. It ramifies on the ala of the nose, supplying the skin, muscles, and alar cartilages, and anastomosing with the angular branch, with the dorsal nasal branch of the ophthalmic, and with branches of the spheno-palatine artery.

() The angular artery is the continuation of the external maxillary beyond the origin of the lateral nasal branch. It runs upwards, in the angular head of the quadratus labii superioris, to the medial commissure of the eye, where it anastomoses with the lateral nasal, and with the nasal and palpebral branches of the ophthalmic artery.

In addition to the above-named branches another branch, formerly called the inferior labial, springs from the anterior aspect of the external maxillary below the level of the alveolar border of the mandible. This vessel runs medially, under cover of the muscles of the lower lip, and it anastomoses with the mental branch of the inferior alveolar artery, with the inferior labial (O.T. inferior coronary), and with its fellow of the opposite side.

(4) Arteria Occipitalis.-The occipital artery (Figs. 759, 760, 787) arises from the posterior aspect of the external carotid artery, below the posterior belly of the digastric muscle, and terminates, near the medial end of the superior nuchal line of the occipital bone, by dividing into medial and lateral terminal branches.

Course. It commences in the carotid triangle and runs upwards and posteriorly, parallel with and under cover of the posterior belly of the digastric, to the interval between the transverse process of the atlas and the base of the skull; there it turns posteriorly, in a groove on the lower surface of the mastoid portion of the temporal bone; as it leaves the groove it alters its direction and runs upwards and medially, on the superior oblique muscle, to the junction of the medial and intermediate thirds of the superior nuchal line of the occipital bone, where it pierces the deep fascia of the neck and enters the superficial fascia of the scalp.

Relations. In the first or ascending part of its course the occipital artery crosses successively the internal carotid artery, the hypoglossal nerve, the vagus nerve, the internal jugular vein, and the accessory nerve; it is covered by the lower fibres of the posterior

belly of the digastric, and the anterior part of the sterno-mastoid muscle, and, close to its origin, it is crossed by the hypoglossal nerve. In the second and more horizontal part of its course, it is still under cover of the sterno-mastoid and digastric, and lies, medially, against the rectus capitis lateralis, which separates it from the vertebral artery. In the third part of its course it rests upon the superior oblique and semispinalis capitis (O.T. complexus), under cover of the sterno - mastoid, the splenius capitis, and the longissimus capitis muscles. Near its termination it is crossed by the great occipital nerve, and it passes either through the trapezius or between the trapezius and the sterno-mastoid, and pierces the deep fascia of the neck before it enters the superficial fascia of the scalp. Branches. (a) Muscular branches go to the surrounding muscles. The sternomastoid branch is the most important of this group; it springs from the commencement of the occipital, is looped downwards across the hypoglossal nerve, and is continued downwards and posteriorly, below and anterior to the accessory nerve, into the sterno-mastoid muscle, where it anastomoses with the sterno-mastoid branch of the superior thyreoid artery. It is sometimes represented by two or more small branches.

(b) The meningeal are irregular branches given off from the occipital, anterior to the mastoid process. They enter the posterior fossa of the skull through the hypoglossal canal, or through the jugular foramen; they supply the upper part of the internal jugular vein, the sigmoid part of the transverse sinus, and the dura mater in the posterior fossa of the skull, and they anastomose with the middle meningeal and with meningeal branches of the ascending pharyngeal artery.

(c) The mastoid, a small and inconstant branch which arises posterior to the mastoid process. It enters the posterior fossa of the skull through the mastoid foramen, supplies the dura mater, and anastomoses with branches of the middle meningeal artery.

(d) The descending branch (O.T. princeps cervicis) is given off from the occipital upon the surface of the superior oblique. It passes medially, and at the lateral border of the semispinalis capitis it divides into superficial and deep branches. The superficial branch runs over the semispinalis capitis, between it and the trapezius, and anastomoses with the superficial cervical artery. The deep branch passes between the semispinalis capitis and the underlying semispinalis cervicis, and anastomoses with branches of the vertebral and profunda cervicis arteries.

(e) The auricular is an inconstant branch which, as a rule, is only given off from the occipital when the posterior auricular artery is absent. It ramifies over the mastoid part of the temporal bone, and supplies the medial surface of the auricle.

(f) The terminal branches (rami occipitales) are medial and lateral. They ramify in the superficial fascia of the posterior part of the scalp, where they anastomose with the posterior auricular and superficial temporal arteries. Both branches are accompanied by branches of the great occipital nerve. The medial branch gives off a meningeal twig, which passes into the skull through the parietal foramen, to supply the walls of the superior sagittal sinus and to anastomose with the middle meningeal artery.

(5) Arteria Auricularis Posterior. The posterior auricular artery (Figs. 759, 760, 787) springs from the posterior aspect of the external carotid immediately above the posterior belly of the digastric muscle, and it terminates between the mastoid process and the back of the auricle by dividing into mastoid and auricular branches.

Course and Relations. Commencing at the upper border of the posterior belly of the digastric, it runs upwards and posteriorly, under cover of the posteromedial surface of the parotid gland, to the interval between the mastoid process and the external acoustic meatus. It is accompanied in the terminal part of its course by the posterior auricular branch of the facial nerve.

Branches. (a) Muscular branches are given to the sterno-mastoid, the digastric, and the styloid group of muscles.

(6) Parotid branches pass to the lower and posterior part of the parotid gland.

(c) A stylo-mastoid branch is given off at the lower border of the external acoustic meatus. It runs upwards, by the side of the facial nerve, enters the stylo-mastoid foramen, and ascends, in the canalis facialis (Fallopius), to the upper part of the medial wall of the tympanum, where it terminates by anastomosing with the petrosal branch of the middle meningeal artery. It supplies branches to the external acoustic meatus, the mastoid cells, the vestibule, and semicircular canals, the stapedius muscle, and a posterior tympanic branch which anastomoses with the anterior tympanic branch of the internal maxillary, forming, in young subjects, a vascular circle around the membrana tympani ; other branches