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mediastinum, through which it ascends, lying anterior to the vertebral column and to the right of the median plane, to the level of the fifth thoracic vertebra ; it then crosses somewhat abruptly from the right to the left of the median plane, and ascends through the superior mediastinum to the root of the neck, where it turns laterally, between the vertebral and common carotid arteries, and it terminates, at the medial border of the left scalenus anterior, by joining the left innominate vein at its commencement.

Length and Diameter.—The total length of the duct averages about 45 cm. (18 inches). It is dilated at both its origin and termination. As a rule it is narrowest opposite the fifth thoracic vertebra, but its calibre is very variable, and sometimes the thoracic portion is broken up into a series of anastomosing channels. The widest portion of the tube is usually the cisterna, but occasionally that dilatation is entirely absent. The duct is provided with several valves, formed by semilunar folds of the tunica intima, arranged in pairs, and the most perfect of them is situated at or near the orifice of communication with the left innominate vein.

Relations.In the abdomen the cisterna chyli lies anterior to the upper two lumbar vertebræ and the corresponding lumbar arteries, between the aorta on the left and the vena azygos and the right crus of the diaphragm on the right. In the posterior mediastinum the thoracic duct is separated from the vertebral column and the anterior longitudinal ligament by the right aortic intercostal arteries and the transverse parts of the hemiazygos and accessory hemiazygos veins; it is covered, in front, in the lower part of its extent by the right pleural sac, and in the upper part by the æsophagus; to its right is the vena azygos, and to its left the descending aorta. In the superior mediastinum it passes forwards from the vertebral column, and it is separated from the left longus colli muscle by a mass of fatty tissue; the æsophagus lies in front of it in that region, but the left margin of the duct projects beyond the æsophagus, and is in relation anteriorly, and from below upwards, with the termination of the arch of the aorta, the left subclavian artery and the pleura. As the duct enters the root of the neck it passes behind the left common carotid artery, whilst to its right and somewhat anterior is the æsophagus, and the left pleura is still in association with its left border.

At the root of the neck it arches laterally above the apex of the pleura sac and the first part of the left subclavian artery. It passes anterior to the vertebral artery and vein, the roots of the inferior thyreoid, transverse cervical, and transverse scapular arteries, the medial border of the scalenus anterior and the left phrenic nerve, and posterior to the left carotid sheath and its contents.

Tributaries. — The cisterna chyli commonly receives five tributaries. (1) Truncus Intestinalis.— The intestinal trunk, which is formed by the efferents of mesenteric and upper pre-aortic glands, and which conveys lymph from the lower and anterior part of the liver, the stomach, the small intestine, the spleen, and the pancreas. (2) Two trunci lumbales, one on each side; they are formed by the efferents of the lumbar glands. They carry lymph from the lower extremities, from the deep portions of the abdominal and pelvic walls, the large intestine and the pelvic viscera, and from the kidneys, suprarenal glands, and genital glands. (3) Two descending lymphatic trunks, one on each side, each of which is formed by the efferent vessels from the corresponding lower intercostal glands; these descend to the cisterna through the aortic opening of the diaphragm. Occasionally they unite to form a single trunk, and in others they, or the tributaries from which they are usually formed, open directly into the thoracic duet (Figs. 797, 798).

In its course through the posterior mediastinum the thoracic duct receives efferents from the upper and posterior part of the liver, and from the posterior mediastinal and esophageal glands; the latter carry lymph from the cesophagus, the pericardium, and the left side of the thoracic wall.

In the superior mediastinum the vessels which open into it are derived from the upper left intercostal glands; it receives lymph also from the heart and left lung by efferents from the left peritracheo-bronchial glands and the intertracheobronchial glands, but the efferents of those glands may unite with the internal mammary lymphatic to form a common trunk which may open either into the thoracic duct or into the innominate vein. In the superior mediastinum, therefore, it may receive lymph from the upper and median part of the abdominal wall,

the liver, the diaphragm, the wall of the thorax, and the mammary gland of the left side, the thymus, the pericardium, the left lung, and the left part of the heart.

At the root of the neck, just before its termination, it receives the efferents from the glands of the left superior extremity, which frequently unite to form a subclavian trunk, and the left jugular trunk, which conveys the lymph from the left side of the head and neck; but either of those vessels or both of them may end separately in the innominate vein.

Ductus Lymphaticus Dexter.— The right lymph duct (Fig. 798) is not always present. It is a short trunk, from 12 to 17 mm. (half to three-quarters of an inch) in length, which lies at the right side of the root of the neck along the medial border of the right scalenus anterior, and it is formed by the confluence of (1) the right jugular trunk, (2) the right subclavian trunk, and (3) the right bronchomediastinal trunk, which carries lymph from the bronchial, the posterior, and the anterior mediastinal and the sternal glands. It thus receives lymph from the right side of the head and neck, the right upper limb and the right side of the trunk, including the upper part of the thoracic wall, the right lung and pleura, the right half of the heart and pericardium, the right side of the diaphragm, and the upper surface of the liver. As a rule, the right lymph duct is not present as a definite stem, and the right jugular trunk carrying the lymph from the head and neck, the right subclavian trunk bearing lymph from the right upper extremity, and the right broncho-mediastinal trunk, end separately in the upper part of the right innominate vein, but any two of the three main trunks of the right side may unite together. The right broncho-mediastinal trunk frequently communicates, below, with the thoracic duct.

LYMPH GLANDS OF HEAD AND NECK.

THE LYMPH GLANDS OF THE HEAD.

All the lymph glands of the head are extracranial.

Lymphoglandulæ Occipitales.—The occipital lymph glands, two or three in number, lie, in or deep to the deep fascia, upon the upper part of the trapezius muscle, or, if the trapezius is small, upon the upper part of the semispinalis capitis or on the splenius muscle. They receive afferent vessels from the occipital region of the scalp and from the superficial parts of the upper and back portion of the neck. Their efferents terminate in the deep cervical glands. Some of the lymph vessels of the occipital region pass directly to the deep cervical glands (Fig. 799).

Lymphoglandulæ Auriculares Posteriores.—The posterior auricular lymph glands (O.T. mastoid) lie on the upper part of the sterno-mastoid muscle and on the mastoid portion of the temporal bone, and they are bound down by a sheathing of deep cervical fascia. They receive afferent vessels from the posterior part of the parietal region of the scalp, and from the medial surface of the auricle. Their efferents join the superficial and the deep cervical glands (Fig. 799).

Lymphoglandulæ Auriculares Anteriores.—The anterior auricular lymph glands (O.T. parotid) lie both superficial and deep to the parotid fascia on the lateral surface of the parotid gland. They receive afferents from the frontal and the temporal regions of the scalp, from the eyebrow, the upper and lower eyelids, the upper part of the cheek, the root of the nose, and the lateral surface of the auricle. Their efferents pass to the superficial and the upper deep cervical glands, and to the parotid lymph glands (Fig. 799).

Lymphoglandulæ Parotideæ.—The parotid lymph glands (O.T. deep parotid glands) lie embedded in the deeper parts of the parotid gland. They receive aferents from the external acoustic meatus, the tympanum, the soft palate, the posterior part of the nose, and the deeper portions of the cheek. Their efferents open into the upper deep cervical glands.

The Superficial Facial Lymph Glands.—Several lymph glands, or groups of lymph glands, have been found in the region of the face but, apparently, they are irregular, both in occurrence and in position. Those which appear to be most

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frequently found are: Infra-orbital, which lie along the angle between the nose and the cheek, and below the margin of the orbit. Their afferents are derived from the surrounding parts; and their efferents pass to the anterior auricular and the submaxillary lymph glands. Buccinator lymph glands have been found on the superficial surface of the anterior part of the buccinator, both anterior and posterior to the anterior facial vein. Those posterior to the vein usually lie close to the point where the parotid duct turns, medially, round the anterior border of the masseter. They receive lymph from the eyelids and cheeks, and transmit it

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Fig. 799.-LYMPH GLANDS OF THE HEAD AND NECK AS SEEN WHEN THE STERNO-MASTOID IS IN ITS

USUAL POSITION, The occipital and the posterior and anterior auricular glands are inserted in accordance with descriptions. The other glands were present in one or other of the two bodies from which the drawing was made. Compare Fig. 801.

to the anterior auricular glands. Supra-mandibular lymph glands lie superficial to the mandible at the anterior border of the masseter, between the anterior facial vein and the external maxillary artery. They receive lymph from the region of the lower lip, and transmit it to the anterior auricular and superficial cervical glands.

Lymphoglandulæ Faciales Profundæ.— The deep facial lymph glands are very variable both in number and size; they lie in association with the internal maxillary artery on the external pterygoid muscle, or on the adjacent part of the wall of the pharynx. Their afferent vessels are derived from the orbit, the temporal fossa, the infra-temporal fossa, the palate, the nose, and the cerebral meninges. Their efferent vessels open into the upper deep cervical glands.

Lymphoglandulæ Linguales.- The lingual lymph glands lie between the genioglossi muscles and, on the lateral surfaces of the hyo-glossi and genio-glossi muscles, deep to the mylo-hyoid muscles; they are simply small lymph nodules interposed in the course of the lymphatics which are passing from the tongue and the floor of the mouth to the deep cervical glands.

THE LYMPH GLANDS OF THE NECK. Lymphoglandulæ Cervicales Superficiales.—The superficial cervical lymph glands lie on or are embedded in the deep fascia along the course of the external jugular vein, superficial to the sterno-mastoid (Fig. 799). They receive afferent vessels from the superficial tissues of the neck, the posterior and anterior auricular, and the submaxillary lymphatic glands. Their efferent vessels terminate in the upper deep cervical glands and the supra-clavicular glands. The uppermost superficial cervical glands are sometimes described as infra-auricular glands.

Lymphoglandulæ Submaxillares.—The submaxillary lymph glands vary in number from three to six. They lie under cover of the deep fascia of the neck, in the angle between the lower border of the mandible and the submaxillary gland, and the largest of the series is usually situated near the point where the external maxillary artery turns round the lower border of the mandible (Fig. 800). Occasionally some smaller gland nodules are found on the deep surface of the submaxillary gland, but these are comparatively rare. The afferent vessels of the submaxillary lymph glands carry lymph from the side of the nose, the upper lip, the lateral part of the lower lip, the anterior third of the border of the tongue, the gums, the submaxillary and sublingual glands, and the adjacent parts of the floor of the mouth. The efferents descend, over the superficial surface of the submaxillary gland, and terminate in the upper deep cervical glands, more particularly in those in the immediate neighbourhood of the termination of the common carotid artery.

Paramandibular Lymph Gland.—This term is applied to one or more lymph glands which lie inside the capsule of the submaxillary gland, in close relation with the gland or embedded in its substance. They receive lymph from the gland and the adjacent parts of the mouth and transmit it to the submaxillary and deep cervical glands.

The Submental Lymph Glands lie below the chin, superficial to the mylo-hyoid muscles and between the anterior bellies of the two digastric muscles. There are usually two on each side, a medial or superior close to the median plane, and a lateral or inferior on the anterior border of the anterior belly of the digastric. They are apt to become enlarged in diseased conditions of the middle part of the lower lip, the adjacent part of the gums, the anterior part of the floor of the mouth, the tip of the tongue, and the skin beneath the chin, for their afferent vessels drain those parts. The efferents from this group of glands pass partly to the submaxillary lymph glands, and partly to a deep cervical gland situated on the superficial surface of the internal jugular vein at the level of the cricoid cartilage (Figs. 799, 800, 801).

Lymphoglandulæ Retropharyngeæ.—The retro-pharyngeal lymph glands lie posterior to the upper part of the pharynx, embedded in the fascia covering the superior constrictor muscle. They are separable into two groups, lateral and median

The lateral retro-pharyngeal glands, 1-3, appear to be constant both in children and adults. Each lateral gland, or group of glands, lies at the level of the atlas, anterior to the upper part of the longus capitis, and posterior to the internal carotid artery.

The median retro - pharyngeal glands, commonly present in children and frequently absent in adults, lie at the same level as the lateral glands, but in the median plane. They are irregular in number and size.

The retro-pharyngeal lymph glands receive lymph from the adjacent muscles and bones, from the nasal part of the pharynx, from the auditory tube and tympanum, and from the posterior parts of the nasal cavities. Their efferents pass to the medial and the lateral deep cervical glands.

Lymphoglandulæ Cervicales Anteriores. --The lymph glands of the anterior part of the neck are separable into two groups, superficial and deep.

The superficial anterior cervical lymph glands are very irregular in number and size. When they are present they lie in association with the anterior jugular veins. The exact origin of their afferents and the terminations of their efferents are unknown, but it is probable that they receive lymph from the superficial tissues of the anterior parts of the neck, and transmit it to the lower deep cervical glands.

The deep anterior cervical lymph glands are

(a) Infra-hyoid glands, which lie anterior to the hyo-thyreoid membrane. They receive lymph from the region of the epiglottis and transmit it to the deep cervical glands. They are not constantly present.

(6) The prelaryngeal gland, which lies either anterior to the cricoid cartilage or to the crico-thyreoid ligament. Its occurrence is very constant. It receives

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lymph from the anterior part of the larynx and from the isthmus and the adjacent parts of the right and left lobes of the thyreoid gland. Its efferents terminate in the deep cervical and the pretracheal glands.

(c) The pretracheal lymph glands are numerous small nodules which lie along the inferior thyreoid veins. They receive lymph from the trachea, the lower part of the larynx, and from the lobes and the isthmus of the thyreoid gland; and they transmit it to the lower deep cervical glands.

(d) The paratracheal lymph glands lie along the sulcus between the larynx and the trachea, anteriorly, and the pharynx and esophagus, posteriorly, in association with the branches of the superior and inferior thyreoid arteries and the recurrent nerves. They receive lymph from the adjacent parts and transmit it to the deep cervical glands (Fig. 800).

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