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arteries. The anterior and posterior branches of the middle meningeal arteries and their ramifications are separated from the bone by corresponding veins.

(d) An accessory meningeal branch may arise either directly from the first part of the internal maxillary or from its middle meningeal branch. It passes upwards, on the medial side of the external pterygoid muscle, enters the middle fossa of the skull through the foramen ovale, supplies the semilunar ganglion and the dura mater, and terminates by anastomosing with branches of the middle meningeal and internal carotid arteries.

(e) The inferior alveolar is a branch of moderate size which passes downwards, between the spheno-mandibular ligament and the mandible, to the mandibular foramen. It is accompanied by the inferior alveolar nerve, which lies in front of it. After entering the foramen it descends in the mandibular canal, and terminates at the mental foramen by dividing into mental and incisive branches.

Branches.-Before it enters the mandibular foramen it gives off two branches.

(i.) The lingual, a small twig, to the buccal mucous membrane, which accompanies the lingual nerve. (ii.) The mylo-hyoid, a small branch which is given off immediately above the mandibular foramen. It pierces the spheno-mandibular ligament, and descends in the mylo-hyoid groove, in company with the mylo-hyoid nerve, to the floor of the mouth, where it anastomoses

, on the superficial surface of the mýlo-hyoid muscle, with the submental branch of the external maxillary artery.

In the mandibular canal the following branches are given off :

(i.) Molar branches to the molar teeth. (ii.) Premolar branches to the premolar teeth. (iii.) The incisive terminal branch, which supplies the incisor and canine teeth and anastomoses with its fellow of the opposite side. (iv.) The mental terminal branch, which passes through the mental foramen, emerges beneath the quadratus labii inferioris, and anastomoses with its fellow of the opposite side, with the inferior labial, and with the submental arteries.

From the second part.—(a) The masseteric, a small branch which passes laterally, through the mandibular notch, to the deep surface of the masseter muscle. It anastomoses in the substance of the muscle with branches of the transverse facial and with the masseteric branches of the external maxillary artery.

(6) Deep Temporal. --Two in number, anterior and posterior. They ascend, in the temporal fossa, between the temporal muscle and the squamous portion of the temporal bone, supplying the muscle and anastomosing with the temporal and lacrimal arteries, and, through the substance of the temporal bone, with the middle meningeal artery.

(c) Small pterygoid branches supply the internal and external pterygoid muscles.

(d) The buccinator branch, a long, slender branch which passes obliquely forwards and downwards with the buccinator nerve. It supplies the buccinator muscle, the skin and mucous membrane of the cheek, and anastomoses with the buccal branches of the external maxillary artery.

From the third part.a) A posterior superior alveolar branch descends in the infratemporal fossa, on the posterior surface of the maxilla, and ends in branches which supply the molar and premolar teeth and the mucous membrane of the maxillary sinus; they also give twigs to the gums and to the buccinator muscle.

(6) An infra-orbital branch commences in the pterygo-palatine fossa. It enters the orbit through the inferior orbital fissure, and runs forwards in the infra-orbital groove and canal to the infra-orbital foramen, through which it emerges on the face, deep to the quadratus labii superioris. Whilst in the infra-orbital groove it gives branches to the inferior rectus and the inferior oblique muscles and the lacrimal gland. In the infra-orbital canal it gives small twigs to the incisor and canine teeth (aa. alveolares superiores anteriores) and to the maxillary sinus. In the face it sends branches upwards to the lower eyelid, to the lacrimal sac, and to the frontal process of the maxilla ; these anastomose with branches of the ophthalmic and external maxillary arteries ; other branches run downwards to the upper lip, where they anastomose with the superior labial artery ; lastly, some branches run laterally into the cheek to unite with the transverse facial and the buccinator arteries.

(c) The descending palatine runs downwards, through the pterygo-palatine fossa, enters the pterygo-palatine canal, and becomes the great palatine artery, which supplies the mucous membrane of the roof of the mouth. As it descends it gives off the artery of the pterygoid canal, and several small twigs which pass through the accessory palatine canals to supply the soft palate, and to anastomose with the ascending palatine and tonsillar branches of the external maxillary and with the ascending pharyngeal artery. The great palatine artery, which is the continuation of the descending palatine, runs forwards in the roof of the mouth, medial to the alveolar process, to terminate in a small branch, which ascends through the incisive foramen and anastomoses with the posterior artery of the septum nasi, which is a branch of the spheno-palatine artery. In its course forwards in the roof of the mouth the great palatine artery supplies the gums and the mucous membrane of the hard palate, and also the palatine and maxillary bones.

(d) The artery of the pterygoid canal is a long, slender branch, usually given off from the descending palatine ; it runs backwards through the pterygoid canal with the corresponding nerve (Vidian), and supplies branches to the upper part of the pharynı, to the levator and tensor veli palatini muscles, and to the auditory tube. One of the latter branches passes along the wall of the auditory tube to the tympanic cavity, where it anastomoses with the other tympanic arteries.

(e) The pharyngeal branch is a small artery which runs backwards, with the pharyngeal branch of spheno-palatine ganglion, through the pharyngeal canal to the roof of the pharynx. It supplies the upper and posterior part of the roof of the nose, the roof of the pharynx, the sphenoidal sinus, and the lower part of the auditory (Eustachian) tube, and anastomoses with the pterygoid branch of the internal carotid.

(1) The spheno-palatine branch springs from the termination of the internal maxillary artery. It passes medially, through the spheno-palatine foramen, into the nasal cavity, where it gives off (a) a branch to the sphenoidal sinus, and (6) a branch which may replace the pharyngeal artery and which has a similar course and distribution. Then it divides into lateral and septal posterior nasal branches. The lateral posterior nasal branches supply the lateral wall of the nasal cavity and the sinuses which open through it, and they anastomose with the posterior and anterior ethmoidal arteries and the lateral nasal branch of the external maxillary. The septal posterior nasal branch accompanies the posterior septal nerve across the roof of the nasal cavity and then anteriorly and downwards in the groove on the vomer. It anastomoses with the great palatine artery and the septal branch of the superior labial.

ARTERIA CAROTIS INTERNA.

The internal carotid artery (Figs. 759, 761, 764, and 788) commences at the termination of the common carotid, opposite the upper border of the thyreoid cartilage, and terminates in the middle fossa of the skull, close to the commencement of the stem of the lateral fissure (Sylvius), where it divides into the middle and anterior cerebral arteries.

Course. From its origin in the carotid triangle it ascends to the base of the skull, lying first in the carotid triangle, medial to the anterior border of the sterno-mastoid, and then between the areolar tissue behind the lateral border of the pharynx, medially, and the posterior belly of the digastric and the styloid process and its muscles laterally. At its commencement it lies postero-lateral to the external carotid, but as it ascends it gradually passes to the medial side of the external carotid, from which it is separated by the styloid process, the stylopharyngeus muscle, the glosso-pharyngeal nerve, and the pharyngeal branch of the vagus.

At the base of the skull it enters the carotid canal, in which it ascends, anterior to the tympanum and the cochlea ; then it turns antero-medially to the apex of the bone where it enters the foramen lacerum, through which it ascends, along the side of the body of the sphenoid, to the middle fossa of the cranium.

In the middle fossa it runs forwards, in the lateral wall of the cavernous sinus, to the small wing of the sphenoid; there it turns backwards along the medial border of the anterior clinoid process, which it grooves. At the posterior extremity of the process it turns upwards to its termination at the medial end of the stem of the lateral fissure (Sylvius), below the medial part of the anterior perforated substance.

Relations. The relations of the various parts of the artery require separate consideration

In the Neck. - Posterior.- The longus capitis (0.T. rectus capitis anticus major), the prevertebral fascia, and the sympathetic trunk separate it from the transverse processes of the cervical vertebræ, and postero-lateral to it are the internal jugular vein and the vagus nerve. The accessory and the glossopharyngeal nerves are also postero-lateral to the artery for a short distance, in the upper part of the neck, where they intervene between it and the internal jugular vein. Medial or deep to the internal carotid is the external carotid artery for a short distance below, and afterwards the wall of the pharynx, the areolar tissue posterior to the wall of the pharynx, the ascending pharyngeal artery, the pharyngeal plexus of veins, and the external and internal laryngeal nerves. Just before it enters the temporal bone the levator palati muscle is to its medial side. Lateral or superficial to it are the sterno-mastoid, skin, and fasciæ, and it is crossed under cover of the sterno-mastoid, from below upwards, by the hypoglossal nerve, the occipital artery, and the posterior auricular artery. It is also crossed superficially, between the lastmentioned arteries, by the digastric and stylo-hyoid muscles, which separate it from the parotid gland, and below the digastric it is covered by the lower part of the postero-medial surface of the gland. Passing obliquely across its anterior lateral surface, and separating

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Fig. 761.—THE CAROTID, SUBCLAVIAN, AND VERTEBRAL ARTERIES AND THEIR Main BRANCHES.

it from the external carotid artery, are the following structures, viz., the stylo-pharyngeus, the styloid process, or the styloglossus muscle, and the glossopharyngeal nerve, the pharyngeal branch of the vagus, and some sympathetic twigs.

In the Carotid Canal.The artery, as it passes upwards, is antero inferior to the cochlea and the tympanum ; postero-medial to the auditory (Eustachian) tube and the canal for the tensor tympani ; and below the semilunar ganglion. The thin lamina of bone which separates it from the tympanum is frequently perforated, and that between it and the semilunar ganglion is frequently absent. In its course through the canal it is accompanied by small veins and sympathetic nerves. The veins receive tributaries from the tympanum, and communicate above with the cavernous sinus and below with the internal jugular vein. The nerves are branches of the nervus caroticus internus, which is the upward continuation of the sympathetic trunk ; they form a plexus around the artery, called the internal carotid plexus.

As it enters the cavity of the cranium the internal carotid artery pierces the external layer of the dura mater and passes between the lingula and the sixth cerebral nerve laterally, and the posterior petrosal process of the body of the sphenoid medially. In the Cranial Cavity. — The artery runs forwards, in the lateral wall of the cavernous sinus, in relation with the oculo-motor, trochlear, the ophthalmic division of the trigeminal, and the abducens nerves laterally, and with the endothelial wall of the sinus medially. When it reaches the lower root of the small wing of the sphenoid it turns upwards to the medial side of the anterior clinoid process, pierces the inner layer of the dura mater, and comes into close relation with the inferior surface of the optic nerve immediately posterior to the optic foramen. It then turns abruptly backwards below the optic nerve, and on the medial side of the anterior clinoid process which it frequently grooves; inclining laterally, it runs between the optic and oculo-motor nerves, and below the anterior perforated substance, to the medial end of the stem of the lateral fissure (Sylvius), where it turns upwards, at some distance from the corresponding lateral border of the optic chiasma, and, after piercing the arachnoid, divides into its two terminal branches, the anterior and middle cerebral arteries.

58 b

BRANCHES OF THE INTERNAL CAROTID ARTERY. Branches are given off from the internal carotid in the temporal bone and in the cranium, but, as a rule, no regular branches are given off in the neck.

In the Temporal Bone.—(1) A carotico-tympanic branch, very small, perforates the posterior wall of the carotid canal, and anastomoses in the tympanum with the stylo-mastoid artery and with the tympanic branches of the internal maxillary and ascending pharyngeal arteries.

(2) A small and inconstant branch which accompanies the nerve of the pterygoid canal (Vidian); it anastomoses with a branch of the descending palatine artery.

In the Cranium.—(1) Cavernous, small branches to the walls of the cavernous sinus and to the oculomotor, trochlear, trigeminal, and abducens nerves.

(2) Minute twigs which supply the semilunar ganglion.
(3) Hypophyseal branches pass to the hypophysis (O.T. pituitary body).

(4) Meningeal branches ramify in the dura mater of the middle cranial fossa, anastomosing with the branches of the middle and accessory meningeal arteries.

(5) Arteria Ophthalmica.—The ophthalmic artery (Fig. 761) springs from Intermediate inedial frontal artery Corpus callosum Septum pellucidum

Posterior medial frontal artery

[graphic]

Parieto-occipital Cartery

Middle cerebral artery Temporal branch of middle cerebral

Posterior cer-
ebral artery

Calcarine artery Pedunculus Temporal branches of posterior cerebral cerebri

Fig. 762.—DISTRIBUTION OF THE CEREBRAL ARTERIES ON THE MEDIAL AND INFERIOR SURFACES

OF THE CEREBRAL HEMISPHERES.
The anterior cerebral artery is coloured green, the middle cerebral artery red, and the

posterior cerebral artery orange. the antero-medial side of the internal carotid as it turns upwards on the medial side of the nterior clinoid process. It passes forwards and laterally, below the optic nerve and through the optic foramen into the orbital cavity. In the orbit it runs forwards, for a short distance, on the lateral side of the optic nerve, and it is in relation laterally with the ciliary ganglion and the lateral rectus

muscle; turning upwards and medially, it crosses, between the optic nerve and the superior rectus, to the medial wall of the orbit, where it turns forwards to terminate at the anterior boundary of the cavity by dividing into frontal and dorsal nasal branches. It is accompanied, at first, by the naso-ciliary nerve, and, in the terminal part of its course, by the infra-trochlear nerve.

Branches.—The branches of the ophthalmic artery are numerous. (a) The posterior ciliary, usually six to eight in number, run forwards at the sides of the optic nerve; they soon divide into numerous branches which pierce the posterior part of the sclera ; the majority terminate in the chorioid coat of the eye as the short posterior ciliary arteries, but two of larger size, the long posterior ciliary arteries, run forwards, one on each side of the eyeball, almost in the horizontal plane, between the sclera and the chorioid coat, to the periphery of the iris, where they divide. The resulting branches anastomose together and form a circle at the periphery of the iris, from which secondary branches run inwards and anastomose together in a second circle near the papillary margin of the iris.

(6) The central artery of the retina arises near to, or in common with, the preceding vessels. It pierces the infero-medial aspect of the optic nerve, about 12 mm. (half an inch) posterior to the sclera, and runs in its centre to the retina, where it breaks up into terminal branches. (c) Anterior meningeal. —A small branch which passes backwards through the superior orbital

Ascending parietal artery Ascending frontal arteries

[graphic]

Parieto-occipital

artery

Calcarine artery

Inferior lateral frontal artery

Calcarine artery

Parieto-temporal artery

Temporal branches of middle cerebral FIG. 763.—DISTRIBUTION OF CEREBRAL ARTERIES ON THE CONVEX SURFACE OF THE CEREBRUM. Anterior cerebral artery is coloured green, the middle cerebral red, and the posterior cerebral orange.

fissure into the middle fossa of the cranium, where it anastomoses with the middle and accessory meningeal arteries, and with the meningeal branches of the internal carotid and lacrimal arteries.

(d) The lacrimal artery arises from the ophthalmic on the lateral side of the optic nerve. It runs forwards, along the upper border of the lateral rectus, to the upper lateral angle of the orbit, and in its course gives off glandular branches to the lacrimal gland, muscular branches to the lateral and superior recti, palpebral branches to the upper eyelid and the upper and lateral part of the forehead, temporal and zygomatic branches, which accompany the zygomatico-temporal and zygomatico-facial branches of the zygomatic (temporo-malar) nerve, to the face and the infra-temporal fossa respectively; anterior ciliary branches, which perforate the sclera behind the corneo-scleral junction and anastomose with the posterior ciliary arteries ; and a recurrent meningeal branch, which passes backwards, through the lateral part of the superior orbital fissure, to anastomose, in the middle fossa of the skull, with the middle meningeal artery,

(e) Muscular.— These branches are usually arranged in two sets, lateral and medial. The former supply the upper and lateral, and the latter the lower and medial orbital muscles. They anastomose with muscular branches from the lacrimal and the supra-orbital vessels, and they give off anterior ciliary branches.

(f) The supra-orbital branch is given off as the ophthalmic artery crosses above the optic nerve. It passes round the medial borders of the superior rectus and Ievator palpebræ muscles, and runs forwards, between the levator and the periosteum, to the supra-orbital notch, accompanying the frontal nerve and its supra-orbital branch. Passing through the notch it reaches the scalp, and, after it has perforated the frontalis muscle, it anastomoses with the frontal branches of the superficial temporal and ophthalmic arteries.

(g) Anterior and posterior ethmoidal branches arise from the ophthalmic as it runs forwards along the medial boundary of the orbit. They pass medially, between the superior oblique and the medial rectus. The posterior, which is much the smaller of the two, traverses the posterior ethmoidal canal, and supplies the posterior ethmoidal cells and the posterior and upper part of

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