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ARTERIES OF THE UPPER EXTREMITY.
The main arterial stem of each upper extremity passes through the root of the neck, traverses the axillary space, and is continued through the arm to the forearm. In the forearm its extent is short, for it terminates, opposite the neck of the radius, by bifurcating into the radial and ulnar arteries, which run through the forearm to the hand. That portion of the common trunk which lies in the root of the neck is known as the subclavian artery, the part in the axillary space is termed the axillary artery, whilst the remaining part is called the brachial artery.
On the right side the subclavian artery (Figs. 757, 759, 761, and 766) commences at the termination of the innominate artery, posterior to the sternoclavicular articulation, whilst that on the left side arises from the arch of the aorta, behind the upper half of the manubrium sterni.
The right artery is about 75 mm. (3 inches) long; it lies in the root of the neck. The left artery is about 100 mm. (4 inches) long, and is situated not only in the root of the neck, but also in the superior mediastinal part of the thorax. In the root of the neck each artery arches laterally, across the apex of the lung and behind the anterior scalene muscle, and is divided into three parts, which lie respectively to the medial side, behind, and to the lateral side of the muscle. The extent to which the arch rises above the level of the clavicle varies; not uncommonly it reaches the level of the lower part of the thyreoid gland. The first parts of the subclavian arteries differ materially from each other both in extent and relations. The relations of the second and third parts are similar on the two sides.
The first part of the left subclavian artery springs from the arch of the aorta, posterior to the commencement of the left common carotid and on the left side of the trachea. It ascends almost vertically, in the superior mediastinum, to the root of the neck, where it arches upwards and laterally to the medial border of the scalenus anterior muscle.
Relations.-Posterior.-In the superior mediastinum it is in relation with the lung
Anterior. In front are the left vagus, the left superior cardiac branch of the sympathetic, the left inferior cardiac branch of the vagus, the left phrenic nerve, and the left common carotid artery. It is also crossed obliquely by the left vagus nerve, and it is overlapped on the left side by the left lung and pleura.
Medial.-Medially it is in relation, from below upwards, with the trachea, the left recurrent nerve, the oesophagus, and the thoracic duct, the latter lying in a plane posterior to the œsophagus and the artery.
Laterally it is closely invested by the left pleura, and it ascends in a groove on the medial aspect of the left lung.
At the root of the neck, as it turns laterally, it lies behind the commencement of the left innominate vein, and the termination of the left vertebral vein, the phrenic nerve, the sterno-thyreoid and sterno-hyoid muscles, the anterior jugular vein, and, more superficially, the sterno-mastoid muscle and the deep cervical fascia; the thoracic duct arches obliquely over it; and it lies in front of the apex of the pleural sac and lung.
The first part of the right subclavian artery (Fig. 761) extends from the back of the right sterno-clavicular articulation to the medial border of the scalenus anterior. It is thus limited to the root of the neck.
Relations.-Posterior.-Behind this part of the artery, and intervening between it and the upper two thoracic vertebræ, are the recurrent nerve, the posterior part of the ansa subclavia, and the apex of the right pleural sac. Anterior.-In front it is in relation with the right vagus, the cardiac branches of the vagus and the sympathetic, the anterior portion of the ansa subclavia, the internal jugular and vertebral veins, and more superficially the sterno-hyoid and sterno-thyreoid muscles, the anterior jugular vein, the sternal end of the clavicle, the sterno-clavicular ligaments, and the sterno-mastoid muscle. The recurrent nerve passes below it and intervenes between it and the apex of the pleural sac.
The second part of the subclavian artery, on each side, extends from the medial to the lateral border of the scalenus anterior, behind which it lies.
Relations. Posteriorly and below it is in relation with the pleural sac. Anteriorly it is covered by the anterior scalene and the sterno-mastoid muscles. The anterior scalene separates it from the subclavian vein, which lies at a slightly lower level, from the transverse cervical and transverse scapular arteries, from the anterior jugular vein, and, on the right side, from the phrenic nerve.
The third part of the subclavian artery is the most superficial portion. It extends from the lateral border of the anterior scalene to the outer border of the first rib, lying partly in the clavicular portion of the posterior triangle of the neck and partly behind the clavicle and the subclavius muscle.
Relations. It rests upon the upper surface of the first rib. Immediately posterior to it is the lowest trunk of the brachial plexus, which separates it from the middle scalene muscle. Anterior to it, and at a slightly lower level, lies the subclavian vein. The external jugular vein crosses the medial part of this portion of the artery, and just before its termination it receives the transverse cervical and transverse scapular veins; those vessels also pass superficial to the artery, which is thus covered superficially by venous trunks; it is also crossed vertically, behind the veins, by the nerve to the subclavius muscle. The lateral section of this part of the artery lies posterior to the clavicle and the subclavius muscle. It is crossed anteriorly by the transverse scapular artery, but the layer of deep cervical fascia which binds the posterior belly of the omo-hyoid to the posterior border of the subclavian groove intervenes between the two vessels. More superficially the third part of the artery is covered by the superficial layer of the deep fascia, the supra-clavicular branches of the cervical nerves, the platysma, and the skin.
BRANCHES OF THE SUBCLAVIAN ARTERY.
(1) The vertebral artery is distributed almost entirely to the head and neck and its chief function is to supply the posterior part of the brain. Its description has therefore been given with that of the other cerebral arteries (see p. 905).
(2) Truncus Thyreocervicalis.-The thyreo-cervical trunk (Figs. 757 and 759) arises close to the medial border of the scalenus anterior, from the upper and front part of the subclavian artery, directly above the origin of the internal mammary artery. After a short upward course of about 4 mm. (two lines), it ends, under cover of the internal jugular vein, by dividing into three branches-viz., the inferior thyreoid, the transverse cervical, and the transverse scapular.
(A) Arteria Thyreoidea Inferior.-The inferior thyreoid artery (Figs. 757, 759) ascends along the anterior border of the scalenus anterior, and turns medially, opposite the cricoid cartilage, to the middle of the posterior border of the corre sponding lobe of the thyreoid gland; it then curves medially and downwards, and descends to the lower end of the lobe of the thyreoid gland, where it divides inte ascending and inferior terminal branches.
Relations.—Posterior are the vertebral artery, and the longus colli muscle the recurrent nerve passes either anterior or posterior to the vessel, opposite the lower border of the thyreoid gland. It is covered anteriorly by the carotid sheath, which contains the common carotid artery, the internal jugular vein, and the vagus nerve; the middle cervical ganglion of the sympathetic lies in front of the artery as it bends medially and on the left side the thoracic duct also passes in front of it.
Branches. It gives off the following branches :
(a) Muscular.-Numerous small branches pass to the scalenus anterior, the longus colli, the infra-hyoid muscles, and the inferior constrictor of the pharynx.
(b) The ascending cervical usually springs from the inferior thyreoid near its origin, but it may arise separately from the thyreo-cervical trunk. It ascends, parallel with and medial to the phrenic nerve, in the angle between the longus capitis and the scalenus anterior, to both of which it gives branches. It also gives off spinal branches which pass through the intervertebral foramina to the vertebral canal. It anastomoses with branches of the vertebral, occipital, ascending pharyngeal, and deep cervical arteries. (c) Esophageal. Small branches given to the walls of the oesophagus, which anastomose with the oesophageal branches of the thoracic aorta.
(d) Tracheal branches are distributed to the trachea; they anastomose with branches of the superior thyreoid and with the bronchial arteries.
(e) An inferior laryngeal branch accompanies the recurrent nerve to the lower part of the larynx. It enters the larynx, at the lower border of the inferior constrictor, gives branches to its muscles and mucous membrane, and anastomoses with the laryngeal branch of the superior thyreoid artery.
(f) The ascending terminal branch supplies the posterior and lower part of the thyreoid gland, and anastomoses with branches of the superior thyreoid artery.
(g) The inferior terminal branch is distributed to the lower and medial part of the corresponding lobe of the thyreoid gland. It anastomoses with its fellow of the opposite side and with branches of the superior thyreoid artery.
(B) Arteria Transversa Colli.-The transverse cervical artery (Figs. 759 and 761) arises from the thyreo-cervical trunk and runs upwards and posteriorly across the posterior triangle of the neck to the anterior border of the trapezius; there it divides into a ramus ascendens (O.T. superficial cervical) and a ramus descendens (O.T. posterior scapular). It is very variable in size, and not infrequently the ramus descendens arises separately from the third part of the subclavian.
Immediately after its origin, under cover of the internal jugular vein, it crosses the scalenus anterior, lying superficial to the phrenic nerve and under cover of the sterno-mastoid muscle; on the left side it is also crossed, superficially, by the terminal part of the thoracic duct. Passing from beneath the sterno-mastoid, it enters the lower part of the posterior triangle of the neck, where it lies upon the trunks of the brachial plexus, and, as it runs upwards and backwards to its termination, it passes medial to the posterior belly of the omo-hyoid.
The ascending branch may be a separate vessel which springs from the thyreo-cervical trunk and takes the course described, whilst the descending branch arises from the third part of the subclavian artery and lies at a lower level. In such cases the upper of the two vessels is called the superficial cervical artery and the lower the transverse cervical artery. If the superficial cervical artery is absent it is replaced by the ascending branch of the transverse cervical.
Branches. (a) Small muscular branches to the surrounding muscles.
(6) The ascending branch, usually a slender branch, passes beneath the trapezius; it sends branches upwards and downwards, superficial to the levator scapula and upon the splenius; the ascending branches anastomose with the descending branch of the occipital artery, and the descending branches accompany the accessory nerve and anastomose with the descending branch and transverse scapular artery.
(c) The descending branch runs downwards, deep to the levator scapula and the rhomboid muscles, close to the vertebral border of the scapula. It runs parallel with, and a short distance away from, the dorsal scapular nerve (O.T. nerve to the rhomboid muscles), and it sends branches into the supraspinous, the infraspinous, and the subscapular fossæ, which anastomose with branches of the transverse scapular and subscapular arteries. It also sends branches backwards, through and between the rhomboid muscles, which anastomose with the branches of the ascending division of the transverse cervical and with the posterior branches of the intercostal arteries.
(C) Arteria Transversa Scapulæ.—The transverse scapular artery (O.T. suprascapular) springs from the thyreo-cervical trunk and terminates in the infraspinous fossa of the scapula. As a rule it is smaller than the transverse cervical artery.
Commencing behind the internal jugular vein, it crosses the scalenus anterior and phrenic nerve, and is covered superficially by the sterno-mastoid and the anterior jugular vein; on the left side it lies behind the termination of the thoracic duct also. Continuing, laterally, behind the clavicle, and crossing superficial to the third part of the subclavian artery and the cords of the brachial plexus, it reaches the scapular notch and passes over the superior transverse ligament. Then it descends, with the suprascapular nerve, through the supraspinous fossa and deep to the supraspinatus muscle, and after passing through the great scapular notch, deep to the inferior transverse ligament, it enters the infraspinous fossa, where it anastomoses with the circumflex scapular branch of the subscapular artery and with twigs of the descending branch of the transverse cervical artery.
Branches. (a) Muscular, to the sterno-mastoid, the subclavius, and the muscles on the dorsum of the scapula.
(6) The medullary, a small branch to the clavicle.
the lateral wall of the nasal cavity. The anterior ethmoidal artery passes through the anterior ethmoidal canal with the anterior ethmoidal nerve, enters the anterior fossa of the skull, and crosses the lamina cribrosa of the ethmoid to the nasal slit, through which it reaches the nasal cavity where it descends, with the external branch of the nasal nerve, in a groove on the posterior surface of the nasal bone, and, finally, passes between the lateral cartilage and the lower border of the nasal bone to the tip of the nose. It supplies branches to the membranes of the brain in the anterior cranial fossa as well as to the anterior ethmoidal cells, the frontal sinus, the anterior and upper part of the nasal muco-periosteum, and the skin on the dorsum of the nose.
(h) Palpebral branches, upper and lower, are given off near the termination of the ophthalmic. They are distributed to the upper and lower eyelids, and they anastomose with the lacrimal, supra-orbital, and infra-orbital arteries.
(2) The dorsal nasal terminal branch passes out of the orbit above the medial tarsal ligament. It pierces the palpebral fascia, and terminates on the side of the nose by anastomosing with the angular branch of the external maxillary artery.
6) The frontal terminal branch pierces the palpebral fascia at the upper and medial part of the orbit, and ascends, with the supra-trochlear nerve, in the superficial fascia of the anterior and medial part of the scalp, anastomosing with its fellow of the opposite side and with the supra-orbital artery.
(6) The posterior communicating artery arises from the internal carotid near its termination. It runs backwards, below the optic tract and anterior to the pedunculus cerebri, and, passing above the oculomotor nerve, joins the posterior cerebral artery forming part of the circulus arteriosus (Willis). It gives branches to the optic chiasma, the optic tract, the pedunculus cerebri, the interpeduncular region, the internal capsule, and the optic thalamus. The posterior communicating artery varies much in size; it may be small on one or both sides, sometimes it is very large on one side; occasionally it replaces the posterior cerebral artery, and it sometimes arises from the middle cerebral artery.
(7) The chorioidal is a small branch, which also arises near the termination of the internal carotid; it passes backwards and laterally, between the pedunculus cerebri and the uncus, to the lower and anterior part of the chorioidal fissure which it enters, and it terminates in the chorioidal plexus in the inferior cornu of the lateral ventricle. It supplies the optic tract, the pedunculus cerebri, the uncus, the posterior part of the internal capsule, the tail of the caudate nucleus, part of the lentiform nucleus, and the amygdaloid nucleus.
(8) Arteria Cerebri Anterior.-The anterior cerebral artery is the smaller of the two terminal branches of the internal carotid. It passes forwards and medially, above the optic chiasma and in front of the lamina terminalis, to the commencement of the longitudinal fissure; there it turns round the genu of the corpus callosum, and runs backwards to the parietal lobe of the brain. At the commencement of the longitudinal fissure it is closely connected with its fellow of the opposite side by a wide but short anterior communicating artery. and in the remainder of its course it is closely accompanied by its fellow artery of the opposite side.
Branches. Branches of all the cerebral arteries are distributed both to the basal ganglionic masses of the brain and to the cerebral cortex; they therefore form two distinct groups which do not communicate with one another (a) central or basal; (4) cortical. The branches of the anterior cerebral include:
(a) Central or basal branches.-The antero-medial basal arteries, a small group vessels, constitute the basal branches of the anterior cerebral artery; they pass upwards into the base of the brain, in front of the optic chiasma, and supply the rostrum of callosum, the lamina terminalis, the head of the caudate nucleus, the anterior part of the lentiform nucleus and internal capsule, the columns of the fornix, the septum pellucidium, and the anterior commissure.
(b) Cortical branches. (b) Medial orbital, one or more small branches which supply the medial orbital convolution, the gyrus rectus, and the olfactory lobe.
(62) Anterior medial frontal, one or more branches which are distributed to the a terior and lower part of the medial surface of the superior frontal gyrus, and to the anterior portions of the superior and middle frontal gyri on the lateral surface of the hemisphere.
(63) An intermediate medial frontal is distributed to the posterior part of the medis lateral surfaces of the superior frontal gyrus and to the upper parts of the anterior and posterior central gyri.
(64) The posterior medial frontal runs backwards to the præcuneus. It supplies the corpus callosum, the præcuneus, and the upper part of the superior parietal lobule.
(9) Arteria Cerebri Media. The middle cerebral artery is the larger of the two terminal branches, and the more direct continuation of the internal carotid artery. It passes laterally, in the stem of the lateral fissure (Sylvius), to the surface of the insula, and it divides, in the posterior part of the circular sulcus (Reil), into parieto-temporal and temporal terminal branches.
Branches. (a) The central or basal, which constitute the antero-lateral basal arteries, are numerous and very variable in size. They arise at the base of the brain, Two sets, known as the medial and
in the region of the anterior perforated substance. the lateral striate arteries, are distinguishable.
(a) The medial striate arteries pass upwards through the two medial segments of the lentiform nucleus (globus pallidus) and the internal capsule to terminate in the caudate nucleus. They supply the anterior portions of the lentiform and caudate nuclei and of the internal capsule.
(a2) The lateral striate arteries pass upwards through the lateral segment (putamen) of the lentiform nucleus, or between it and the external capsule, and they form two sets: an anterior, the lenticulo-striate, and a posterior, the lenticulo-optic; both sets traverse the lentiform nucleus and the internal capsule, but the lenticulo-striate arteries terminate in the caudate nucleus, and the lenticulo-optic in the thalamus. One of the lenticulo-striate arteries, which passes in the first instance round the lateral side of the lentiform nucleus, and afterwards through its substance, is larger than its companions; it frequently ruptures, and is known as the "artery of cerebral hemorrhage."
(b) Cortical branches are given off as the middle cerebral artery passes over the surface of the insula at the bottom of the lateral fissure, as follows:
(61) The lateral orbital runs forwards and laterally, and is distributed to the lateral part of the orbital surface of the frontal lobe and to the inferior frontal gyrus. (62) The inferior lateral frontal, which supplies the inferior and middle frontal gyri.
(63) The ascending frontal, which turns round the upper margin of the lateral fissure, and is distributed to the anterior central gyrus and to the posterior part of the middle frontal gyrus.
(64) The ascending parietal branch emerges from the lateral fissure (Sylvius) and passes upwards along the posterior border of the posterior central gyrus, supplying that gyrus and the superior parietal lobule.
(65) The temporal branch passes out of the lateral fissure, and turns downwards to supply the superior and middle temporal gyri.
(66) The parieto-temporal branch continues backwards, in the direction of the main stem of the middle cerebral artery, and emerges from the posterior end of the lateral fissure; it supplies the inferior parietal lobule, part of the lateral surface of the occipital lobe, and the posterior part of the temporal lobe.
The vertebral artery (Figs. 757 and 761) is the first branch given off from the subclavian trunk; it arises from the upper and posterior part of the parent stem, opposite the interval between the anterior scalene and the longus colli muscles, and terminates at the lower border of the pons (Varolii) by uniting with its fellow of the opposite side to form the basilar artery.
Course and Relations.-The vertebral artery is divisible into four parts.
The first part runs upwards and backwards, between the scalenus anterior and the lateral border of the longus colli, to the foramen in the transverse process of the sixth cervical vertebra. It is surrounded by a plexus of sympathetic nerve fibres, is covered anteriorly by the vertebral and internal jugular veins, and it may be crossed anteriorly by the inferior thyreoid artery. On the left side the terminal part of the thoracic duct also passes anterior to it. The second part runs upwards through the foramina in the transverse processes of the upper six cervical vertebræ. As far as the second cervical vertebra its course is almost vertical; as it passes through the transverse process of the epistropheus, however, it is directed obliquely upwards and laterally to the atlas. It is surrounded by a plexus of sympathetic nerve fibres, and also by a plexus of veins. The artery lies anterior to the trunks of the cervical nerves, and medial to the intertransverse muscles.
The third part