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digastric muscle. It crosses forwards, superficial to the occipital and internal and external carotid arteries, immediately below the origin of the superior sterno-mastoid branch of the first-mentioned vessel. The vagus nerve descends vertically, within the carotid sheath, behind and between the carotid vessels and the internal jugular vein; care must be taken not to include it when ligaturing the common carotid or internal jugular. Surgically, the accessory is the most important nerve in the anterior triangle; it enters the substance of the sterno-mastoid muscle 11⁄2 in. below the tip of the mastoid process. A portion of the nerve is resected in the treatment of spasmodic wry-neck, and it is always exposed in the removal of the medial group of deep cervical glands. The course of the nerve may be mapped out upon the surface by drawing a line from a point midway between the tip of the mastoid process and the angle of the mandible to a little above the middle of the posterior border of the sterno-mastoid muscle, and thence across the posterior triangle to the anterior border of the trapezius, beneath which it passes at the level of the seventh cervical spine. The deeper guides to the nerve are the posterior belly of the digastric, and the internal jugular vein which it crosses, very obliquely, from above downwards and backwards below and in front of the transverse process of the atlas (felt as a distinct bony landmark midway between the tip of the mastoid and the angle of the mandible). The cervical sympathetic lies in the posterior wall of the vascular compartment of the neck, and may be reached by an incision along the posterior border of the sterno-mastoid: the anterior surfaces of the roots of the transverse processes of the vertebræ are the deep guides to the nerve.
The cervical plexus, which lies deep to the superior half of the sterno-mastoid upon the levator scapula and scalenus medius muscles, may be exposed through an incision along the posterior border of the upper half of the sterno-mastoid muscle. The phrenic nerve, the most important branch of the cervical plexus, arises one inch above the carotid tubercle and descends almost vertically upon the scalenus anterior; it is overlapped by the lateral margin of the internal jugular vein. Although frequently exposed by the surgeon in removing the lower medial group of deep cervical glands, the phrenic nerve is protected from injury by being covered by the prevertebral fascia.
The muscular or lower carotid triangle is an important triangular intermuscular space bounded by the anterior border of the sterno-mastoid, the anterior belly of the omo-hyoid, and the sterno-hyoid. Behind this space, and forming, as it were, its floor, is a still deeper space bounded by the longus colli and scalenus anterior muscles. It may with advantage be termed the prevertebral intermuscular triangle, or, from the fact that it contains the vertebral artery, it may be termed the vertebral arterial triangle. At its apex is the prominent anterior tubercle of the transverse process of the sixth cervical vertebra. By making an incision along the anterior border of the left sterno-mastoid muscle, and passing through this triangle, the surgeon reaches, in order from before backwards, the internal jugular vein, the common carotid artery, the vagus, the thoracic duct, the middle cervical ganglion of the sympathetic, the inferior thyreoid artery, the vertebral vessels, the recurrent nerve, and the oesophagus. The most important bony landmark in this triangle is the prominent anterior tubercle of the transverse process of the sixth cervical vertebra. The common carotid artery may be compressed against this tubercle, which is therefore termed the "carotid tubercle." It is the most important guide to the vertebral artery, which enters the foramen in the transverse process of the sixth cervical vertebra.
The cervical portion of the œsophagus, which begins at the level of the cricoid cartilage, descends behind, and a little to the left of, the trachea. To expose it, the surgeon, after passing through the above-mentioned muscular triangle, divides the pretracheal fascia, and passes between the trachea and the carotid sheath down to the longus colli muscle medial to the inferior thyreoid artery and vertebral vessels. The lower pole of the corresponding lobe of the thyreoid gland is retracted medially along with the trachea. The oesophagus lies in the loose cellular tissue in front of the prevertebral fascia; hence it can be mobilised sufficiently to admit of its being brought to the surface. The oesophagus may also be exposed through an incision in the median plane, the trachea, which is freely movable, being displaced to
the right side. In opening the oesophagus care must be taken not to injure the recurrent nerve, which ascends in the groove between it and the trachea, and also order that the loose submucous cellular interval must not be mistaken for the lumenep of the tube. The recurrent nerve must be avoided also in operations connected with the thyreoid gland; it is most liable to be injured during the application of a ligature to the inferior thyreoid artery, which arches medially in front of the rar nerve to reach the posterior surface of the gland.
THE THORACIC DUCT.
The thoracic duct, after entering the root of the neck between the oesophagus and the pleura, ascends to about an inch above the clavicle. At this level it arches ac laterally behind the lower part of the carotid sheath in front of the vertebral vessels. Great care must therefore be taken not to injure the duct in removing the lymph glands which lie in the loose cellular tissue behind the inferior part of the internal jugular vein, between it and the vertebral vein at the medial border of the scalenus anterior. In addition to those glands a few small lymph glands lie adjacent to the lateral aspects of the cervical portions of the trachea and oesophagus. They receive their afferent vessels from the larynx, trachea, oesophagus, and thyreoid gland.
The roof of the posterior triangle is formed by the general envelope of deep. cervical fascia, while the fascia which covers the muscles forming its floor, as well as that covering the brachial nerve trunks and the subclavian artery, is a lateral continuation of the prevertebral fascia. The lateral deep cervical and supraclavicular lymph glands are embedded in the cellular tissue between these two layers of fascia. In removing these glands, every endeavour should be made to preserve the motor nerves. The accessory nerve, after entering the posterior triangle at the junction of the superior and middle thirds of the posterior border of the sterno-mastoid muscle, crosses the triangle superficially, and parallel to the levator scapula. It leaves the triangle by passing under cover of the anterior border of the trapezius, at the junction of its middle and inferior thirds. The lesser occipital nerve curves round the accessory from below upwards, superficially, just at the posterior border of the muscle; it furnishes, therefore, a useful guide to the position of that important motor nerve.
The dorsalis scapulæ nerve (O.T. nerve to the rhomboids) crosses the triangle, inferior to the accessory, and enters the septum between the levator scapulæ and scalenus medius muscles.
The supra-scapular nerve is seen arising from the lateral edge of the upper trunk of the brachial plexus, a little above the posterior belly of the omo-hyoid muscle. The loops of the cervical plexus lie under cover of the upper part of the sterno-mastoid muscle, between it and the origins of the levator scapula and the upper part of the scalenus medius muscles.
The posterior belly of the omo-hyoid, which forms the superior boundary the subclavian division of the posterior triangle, passes beneath the posterior border of the sterno-mastoid at a point about one inch above the clavicle. The external jugular vein, usually visible through the skin, runs in a line from the angle of the jaw to the middle of the clavicle; it is the vessel which is generally opened to relieve the right side of the heart in asphyxia. The lumen of the vein is kept patent where it pierces the fascia of the subclavian triangle; hence a wound of the vein in that situation is liable to be followed by the suction of air into the circulation during inspiration. The third part of the subclavian artery can be compressed against the first rib by pressing downwards and backwards, immediately above the clavicle, a little behind the posterior border of the sterno-mastoid muscle. To map out the course of the subclavian artery in the neck, draw a line, convex upwants, from the superior border of the sterno-clavicular articulation to the middle of the clavicle, the highest part of the arch to reach from 1 to 1 in. above the bone. To ligature the vessel in the third part of its course, an angular incision is made along
the middle of the superior border of the clavicle and the inferior part of the posterior border of the sterno-mastoid muscle. The most important guides to the vessel are the posterior belly of the omo-hyoid, the lateral border of the scalenus anterior, and the scalene tubercle of the first rib. The close relation of the vessel to the lowest trunk of the brachial plexus and to the cervical pleura must be kept in mind. In the rare instances in which a cervical rib is present the subclavian artery lies either in front of it, or arches above it, according to the degree of development of the rib. The subclavian vein lies below, and anterior to, the artery, altogether under cover of the clavicle.
Entering the posterior triangle, from behind the lateral border of the scalenus anterior, are the trunks of the brachial plexus. They lie upon the scalenus medius, and can be felt, through the skin, immediately above and behind the third part of the subclavian artery. The anterior ramus of the fifth cervical nerve supplies the rhomboids, the abductors and lateral rotators of the arm, and the flexors and supinators of the forearm; that of the sixth the serratus anterior, the adductors and medial rotators of the arm, and the extensors and pronators of the forearm; that of the seventh the flexors and extensors of the wrist; that of the eighth the flexors and extensors of the fingers; that of the first thoracic all the small muscles of the hand. The carotid tubercle lies between the anterior rami of the sixth and seventh cervical nerves. The fifth and sixth cervical nerves are those which suffer most when the plexus is injured by forcible depression of the shoulder while the head is bent to the opposite side, such as occurs, for instance, in the "Obstetrical Paralyses" of Duchenne.
To expose the trunks of the brachial plexus an incision is made from the junction of the middle and inferior thirds of the posterior border of the sternomastoid downwards and laterally to the junction of the lateral and intermediate thirds of the clavicle.
The relation of the lowest trunk of the brachial plexus to the first rib is important in relation to those forms of brachial neuritis in which the motor and sensory symptoms indicate pressure on the anterior ramus of the first Wood Jones has shown that the sulcus for the subclavian artery on the superior surface of the first rib frequently lodges the lowest trunk of the brachial plexus as well as the artery, and that the more the first thoracic nerve contributed to the plexus the deeper is the sulcus. In two cases the writer has cured the neuralgia and the partial paralysis of the intrinsic muscles of the hand supplied by the first thoracic nerve by removing the portion of the first rib containing the "sulcus nervi brachialis." The symptoms were due to the portion of the first thoracic nerve which goes to join the brachial plexus being stretched and pressed upon by the first rib as it crosses its inner edge to join the eighth cervical nerve. Although similar symptoms may be produced by the first thoracic nerve being stretched across a cervical rib, the surgeon must not expect to find this anomaly in all cases; and when a skiagram has been obtained, care must be taken not to mistake a well-developed posterior tubercle of the transverse process of the seventh cervical vertebra for a foreshortened view of a rudimentary cervical rib.
In the median line of the neck posteriorly is the nuchal furrow, at the bottom of which are the cervical spines and the ligamentum nucha. At the superior part of the furrow, about two inches below the external occipital protuberance, is the large spine of the epistropheus, which can be distinctly felt; a line drawn from it laterally and slightly upwards to the transverse process of the atlas corresponds to the position of the inferior oblique muscle and, therefore, to the inferior margin of the sub-occipital triangle. The course of the deep part of the greater occipital nerve may be mapped out by drawing a line from the centre of the above-mentioned line to a point one inch lateral to the external occipital protuberance. In the floor of the suboccipital triangle is the posterior arch of the atlas upon which the vertebral artery lies.
For the convenience of topographical description, clinicians, by the use of vertical and transverse lines, have arbitrarily divided the surface of the chest into
FIG. 1090.-ANTERIOR ASPECT OF TRUNK, SHOWING SURFACE TOPOGRAPHY OF VISCERA.
M.C. Mid-clavicular line.
P.S. Para-sternal line.
Transpyloric line of Addison.
Common iliac artery.
certain definite regions or areas. The vertical lines are: the mid-sternal, the lateral sternal, the para-sternal, the mammary or mid-clavicular, the anterior, mid, and posterior axillary, and the scapular. The position of the mid- and lateral sternal lines is sufficiently indicated by their names.
The mammary, better termed the mid-clavicular, is drawn vertically downwards from the centre of the clavicle, or, what comes to practically the same thing, from a point midway between the centre of the jugular notch and the tip of the acromion. In the male this line usually lies to in. medial to the centre of the nipple, which is usually placed over the fourth interspace, or fifth rib, four inches from the median plane. In the child the nipple may be as high as the inferior border of the third rib. In the female the position of the nipple is so variable that it is of no topographical value. In a well-proportioned subject, the mid-clavicular line, if prolonged downwards, will be found to be continuous with the vertical or lateral inguinal line, which crosses the costal margin at the tip of the ninth costal cartilage. The para-sternal line, drawn midway between the lateral sternal and midclavicular, crosses the costal margin opposite the tip of the eighth costal cartilage. The anterior, the mid, and the posterior axillary lines are drawn downwards from the anterior fold, the apex, and the posterior fold of the axilla, respectively. The scapular line is drawn perpendicularly through the inferior angle of the scapula.
Of the two transverse lines, the superior, which separates the infra-clavicular and supra-sternal regions from the mammary and infra-sternal regions, is drawn at the level of the third chondro-sternal articulation; the inferior, which separates the mammary and infra-mammary regions, is drawn at the level of the sixth chondrosternal articulation.
The lateral area of the chest is divided into a superior, or axillary, and an inferior or infra-axillary region, by a horizontal line drawn at the level of the sixth rib.
In muscular subjects there is a well-marked median furrow, the sternal furrow, between the sternal origins of the pectoralis major muscles. The medial part of the inferior border of each of these muscles forms a curved prominence which, overlying the fifth rib, corresponds to the junction of the mammary and infra-mammary regions. Below this prominence is the infra-mammary region, which forms a somewhat flat surface, corresponding to the upper part of the rectus muscle. In the axillary and infra-axillary regions are the prominences caused by the digitations of origin of the serratus anterior, the first to appear below the pectoralis major being that which springs from the fifth rib.
The superior border of the sternum lies in the same horizontal plane as the inferior border of the body of the second thoracic vertebra, the distance between the two being about two inches. The junction of the manubrium and the body of the sternum forms a slight prominence or angle, known as the angulus sterni (Ludovici), which, although not usually visible, may always be felt. The angulus lies in the same plane as the body of the fifth thoracic vertebra.
The xiphi-sternal junction corresponds to the fibro-cartilage between the ninth and tenth thoracic vertebræ. Immediately inferior to the xiphi-sternal articulation. is the infra-sternal notch, formed by the junction of the seventh costal cartilages with the sternum. Inferior to the notch is the epigastric fossa or triangle, bounded laterally by the seventh costal cartilages. The apex of the triangle forms an angle which varies considerably according to the shape of the chest, the average being about 70°. Not infrequently the eighth costal cartilage articulates with the sternum.
Fracture of the sternum is rare, and generally occurs at or close to the junction of the manubrium and the body; it may occur either from direct violence, or indirectly along with fracture of the vertebral column. Unlike that of the ribs, the periosteum covering the sternum is firmly adherent to the bone.
The ribs, which in well-nourished subjects cause no surface prominences, are readily visible in thin persons; in the obese they are very difficult to feel. In counting the ribs from the front, the second may always be identified by its relation to the angulus sterni. The first rib is to a large extent under cover of the clavicle. The inferior border of the pectoralis major and the first visible digitation of the