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(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.
(i) 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.
(j) 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 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.
(6) 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
anastomose with tympanic branches from the internal carotid and the ascending pharyngeal arteries, and with the internal auditory branch of the basilar.
(d) The auricular branch ascends medial to the posterior auricular muscle. It gives branches to the auricle and to the scalp in the posterior part of the temporal region, which anastomose with the superficial temporal and occipital arteries. The auricular branches supply both surfaces of the auricle, piercing or turning round the margins of the cartilage to gain the lateral surface, and they anastomose with the anterior auricular branches of the superficial temporal artery.
(e) The occipital branch runs upwards and posteriorly along the insertion of the sterno-mastoid muscle. It supplies the sterno-mastoid and occipitalis muscles, and the skin, and it anastomoses with the occipital artery.
(6) Arteria Pharyngea Ascendens-The Ascending Pharyngeal Artery (Fig. 761).—This artery arises from the medial surface of the lower part of the external carotid, and its terminal branches are distributed to the wall of the pharynx and in the soft palate.
Course. It commences in the carotid triangle, usually as the first or second branch of the external carotid, and it ascends on the wall of the pharynx to the apex of the petrous portion of the temporal bone.
Relations. Medially it is in relation with the constrictor muscles of the pharynx. Posterior to it are the transverse processes of the cervical vertebræ, the sympathetic trunk, and the longus capitis. Laterally it is in relation with the internal carotid artery, and it is crossed by the stylo-pharyngeus muscle, the glossopharyngeal nerve, and the pharyngeal branch of the vagus.
Branches. The branches of this artery are very irregular and inconstant, but the following have received names :
(a) Pharyngeal Branches.-Small twigs which ramify on the walls of the pharynx and supply the middle and superior constrictor muscles, the palatine tonsil, and the lower part of the auditory tube (O.T. Eustachian). They anastomose with branches of the superior thyreoid, lingual, and external maxillary arteries.
(b) Prevertebral. Small branches distributed to the prevertebral muscles and fascia, the deep cervical glands, and the large nerve trunks. They anastomose with the ascending cervical and vertebral arteries.
(c) Posterior Meningeal. One or more small branches which enter the cranium by the hypoglossal canal, the jugular, or the lacerate foramen, and supply the dura mater. They anastomose with branches of the middle meningeal and vertebral arteries.
(d) Inferior Tympanic.—A small artery which accompanies the tympanic branch of the glossopharyngeal nerve to the tympanic cavity, where it anastomoses with the other tympanic arteries.
(e) Palatine. A very variable artery which sometimes replaces the ascending palatine branch of the external maxillary artery. When present it springs from the upper part of the ascending pharyngeal artery, pierces the pharyngeal aponeurosis above the upper border of the superior constrictor muscle, and descends into the soft palate with the levator veli palatini muscle. It supplies the mucous membrane of the supero-lateral part of the pharyngeal wall and the tissues of the soft palate, and it anastomoses with the palatine branches of the internal maxillary, the external maxillary and the lingual arteries.
(7) Arteria Temporalis Superficialis (Fig. 759). The superficial temporal artery, one of the terminal branches of the external carotid, commences between the upper part of the antero-medial surface of the parotid gland, and the neck of the mandible, and terminates in the scalp, from 25 to 50 mm. (1 or 2 inches) above the zygomatic arch, by dividing into a parietal and a frontal branch. Course. The artery ascends over the posterior root of the and zygoma, passes into the superficial fascia of the temporal region. It is accompanied by the auriculo-temporal nerve and by the superficial temporal vein, which usually lies posterior to it. As it crosses the zygoma it is covered by the skin alone, and it may be easily compressed against the subjacent bone.
Branches. (a) Parotid.-Small branches to the upper part of the parotid gland. (6) Articular to the mandibular articulation.
(c) Anterior Auricular. Small branches to the lateral surface of the auricle and to the external acoustic meatus. They anastomose on the surface of the auricle with branches
of the posterior auricular artery, and in the external acoustic meatus with branches of the internal maxillary artery.
(d) Transverse Facial.-A branch of moderate size which emerges from under cover of the upper part of the anterior border of the parotid gland. It runs forwards across the the masseter, below the zygoma and above the parotid duct, accompanied by zygomatic branches of the facial nerve, which may lie either above or below it. It supplies the parotid gland, the masseter, parotid duct, and the skin, and it terminates in branches which anastomose with the infra-orbital and buccinator branches of the internal maxillary artery and with the buccal and masseteric branches of the external maxillary artery.
(e) Middle Temporal.-A branch which usually springs from the commencement of the superficial temporal. It crosses the zygoma, pierces the temporal fascia and the temporal
FIG. 760. THE EXTERNAL CAROTID, INTERNAL MAXILLARY, AND MENINGEAL ARTERIES. muscle, and terminates in the temporal fossa by anastomosing with the deep temporal branches of the internal maxillary artery.
(f) Zygomatico-orbital. This branch may spring directly from the superficial temporal, but it is frequently a branch of the middle temporal. It runs anteriorly, above the zygoma, between the two layers of the temporal fascia. It supplies branches to the orbicularis oculi, and anastomoses, through the zygomatic bone and round the outer margin of the orbit, with the lacrimal and palpebral branches of the ophthalmic artery.
(g) The frontal branch runs forwards and upwards, in a tortuous course, through the superficial fascia of the scalp towards the frontal tuberosity, lying at first upon the temporal fascia, and then upon the galea aponeurotica. It supplies the frontalis and the orbicularis oculi, and anastomoses with the lacrimal and supra-orbital branches of the ophthalmic artery, with the parietal terminal branch of the superficial temporal, and with its fellow of the opposite side.
(h) The parietal branch, less tortuous than the frontal, runs upwards and posteriorly in the superficial fascia of the scalp. It anastomoses, anteriorly, with the frontal terminal branch, posteriorly with the posterior auricular and occipital arteries, and, across the
median line, with its fellow of the opposite side. It supplies the skin and fascia, and the anterior and superior muscles of the auricle.
(8) Arteria Maxillaris Interna. The internal maxillary artery commences between the antero-medial surface of the parotid gland and the neck of the mandible, and terminates in the pterygo-palatine fossa.
Course and Relations. Although the internal maxillary artery is only a short trunk it has many important relations, in the consideration of which it is convenient to divide the vessel into three parts. The first part extends from the back of the neck of the mandible into the infratemporal fossa, as far as the lower border of the external pterygoid muscle. It lies between the spheno-mandibular ligament and the neck of the mandible, along with the auriculo-temporal nerve and the internal maxillary vein. The second part is in the infra temporal fossa, and runs upwards and anteriorly. It may lie on the lateral or the medial side of the lower head of the external pterygoid muscle. In the former case it is situated between the temporal and external pterygoid muscles, and in the latter between the external pterygoid muscle and the branches of the mandibular division of the trigeminal nerve. The third part passes between the upper and the lower heads of the external pterygoid, and through the pterygo-maxillary fissure into the pterygo-palatine fossa.
Branches. From the first part.-(a) Deep auricular. A small branch which arises from the commencement of the artery and passes upwards to the external acoustic meatus. It supplies the mandibular joint, the parotid gland, the external acoustic meatus, and the superficial surface of the tympanic membrane. It anastomoses with branches of the superficial temporal and posterior auricular arteries.
(6) The anterior tympanic, a variable and small branch. It runs upwards and posteriorly, traverses the petro-tympanic fissure (Glaserian), and enters the tympanum through its lateral wall. In the tympanic cavity it anastomoses with tympanic branches from the internal carotid and ascending pharyngeal arteries, and with the stylo-mastoid branch of the posterior auricular, forming with the latter, in young subjects, a circular anastomosis around the tympanic membrane.
(c) Middle Meningeal. The largest branch of the internal maxillary. It ascends between the external pterygoid muscle laterally and the spheno-mandibular ligament and the tensor veli palatini medially; passes between the two roots of the auriculo-temporal nerve and through the foramen spinosum, and enters the middle fossa of the cranial cavity. Before it enters the skull it lies posterior to the third division of the trigeminal nerve, and is accompanied by a vein which also passes through the foramen spinosum. In the middle cranial fossa it passes for a short distance anteriorly, in a groove on the great wing of the sphenoid, between the dura mater and the bone, and divides into anterior and posterior terminal branches.
Branches.(i.) Superficial Petrosal.—A small branch which arises from the middle meningea! soon after it enters the cranium. It passes through the hiatus canalis facialis and anastomoses with the stylo-mastoid branch of the posterior auricular artery; it also sends some small branches into the tympanic cavity.
(ii.) Ganglionic.-Minute branches which supply the semilunar ganglion and the roots of the fifth cerebral nerve.
(iii.) Superior Tympanic.-A small twig which reaches the tympanic cavity through the canal for the tensor tympani muscle, or through the petro-squamous suture.
(iv.) Orbital.—An anastomosing branch which arises, occasionally, from the anterior terminal branch. It passes through the superior orbital fissure into the orbit, and anastomoses with the lacrimal artery.
(v.) Anterior terminal, the larger of the two terminal branches, passes upwards along the great wing of the sphenoid to the sphenoidal angle of the parietal bone, where it is sometimes enclosed in a distinct bony canal; it is continued upwards, a short distance behind the anterior border of the parietal bone, almost to the vertex of the skull, sending branches forwards into the anterior, and backwards towards the posterior cranial fossa.
(vi.) The posterior terminal branch passes posteriorly from the great wing of the sphenoid to the squamous part of the temporal bone, beyond which it ascends to the middle of the inner surface of the parietal bone. It sends branches upwards to the vertex, and backwards towards the posterior cranial fossa.
By means of its various branches the middle meningeal artery anastomoses with its fellow of the opposite side, with meningeal branches from the occipital, ascending pharyngeal, ophthalmic, and lacrimal arteries; also with the stylo-mastoid branch of the posterior auricular, through the substance of the temporal bone, with the accessory meningeal artery, and the deep temporal