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1.   Lymphatic vessels and nodes of thoracic viscera and walls. Thoracic and right lymphatic ducts

2.   Thoracic part of sympathetic trunk and thoracic division of vagus. Intercostal nerves. Innervation of vicsera and walls of thorax

3.   Abdominal aorta. Parietal  and visceral branches

 

Lesson # 29

 

Theme 1.     Lymphatic vessels and nodes of thoracic viscera and walls. Thoracic and right lymphatic ducts

The Lymphatic Vessels of the Thorax

Lymphatic nodes of the thorax may be divided into two sets, parietal and visceral. There distinguish the following parietal nodes of thorax:

1.  Parasternal nodes collect lymph from pericardium, pleura, anterior thoracic wall, diaphragmatic surface of liver, mammary gland. The vessels from these nodes carry lymph into right and left venous angles.

2.  Intercostal nodes empty lymph into thoracic duct, and from superior nodes - into deep lateral jugular lymphatic nodes.

3.  Superior phrenic nodes carry lymph into parasternal nodes, nodes inferior tracheobronchic and into bronchоpulmonary nodes.

4.  Prepericardial nodes transport lymph into parasternal nodes, nodes inferior tracheobronchic and into bronchоpulmonary nodes.

5.  Prevertebral nodes are disposed between backbone and esophagus.

6.  Paramammary nodes are disposed laterally from breasts and drain them.

 

Deep lymph nodes and vessels of the thorax and abdomen (diagrammatic). Afferent vessels are represented by continuous lines, and efferent and internodular vessels by dotted lines.

The visceral lymph nodes include the following groups:

1.  paraesophageal nodes

2.  paratracheal nodes

3.  tracheobronchic nodes

4.  bronchоpulmonary nodes

The tracheobronchial lymphatic nodes.

 

All foregoing visceral nodes of thorax according old anatomic nomenclature, belong to anterior and, especially, posterior mediastinal lymphatic nodes (nodi lymphatici mediastinales anteriores et posteriores). Left half of thoracic cavity is drained to thoracic duct, right half - into right lymphatic duct.

The lymphatic nodes of the thorax may be divided into parietal and visceral—the former being situated in the thoracic wall, the latter in relation to the viscera.

  The parietal lymphatic nodes include the sternal, intercostal, and diaphragmatic nodes.

  1. The Sternal Nodes (lymphoglandulæ sternales; internal mammary glands) are placed at the anterior ends of the intercostal spaces, by the side of the internal mammary artery. They derive afferents from the mamma, from the deeper structures of the anterior abdominal wall above the level of the umbilicus, from the upper surface of the liver through a small group of glands which lie behind the xiphoid process, and from the deeper parts of the anterior portion of the thoracic wall. Their efferents usually unite to form a single trunk on either side; this may open directly into the junction of the internal jugular and subclavian veins, or that of the right side may join the right subclavian trunk, and that of the left the thoracic duct.

  2. The Intercostal Nodes (lymphoglandulæ intercostales) occupy the posterior parts of the intercostal spaces, in relation to the intercostal vessels. They receive the deep lymphatics from the postero lateral aspect of the chest; some of these vessels are interrupted by small lateral intercostal glands. The efferents of the glands in the lower four or five spaces unite to form a trunk, which descends and opens either into the cisterna chyli or into the commencement of the thoracic duct. The efferents of the glands in the upper spaces of the left side end in the thoracic duct; those of the corresponding right spaces, in the right lymphatic duct.

4.   The Diaphragmatic Nodes lie on the thoracic aspect of the diaphragm, and consist of three sets, anterior, middle, and posterior.

 

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  The anterior set comprises (a) two or three small glands behind the base of the xiphoid process, which receive afferents from the convex surface of the liver, and (b) one or two glands on either side near the junction of the seventh rib with its cartilage, which receive lymphatic vessels from the front part of the diaphragm. The efferent vessels of the anterior set pass to the sternal glands.

  The middle set consists of two or three glands on either side close to where the phrenic nerves enter the diaphragm. On the right side some of the glands of this group lie within the fibrous sac of the pericardium, on the front of the termination of the inferior vena cava. The afferents of this set are derived from the middle part of the diaphragm, those on the right side also receiving afferents from the convex surface of the liver. Their efferents pass to the posterior mediastinal glands.

  The posterior set consists of a few glands situated on the back of the crura of the diaphragm, and connected on the one hand with the lumbar glands and on the other with the posterior mediastinal glands.

  The superficial lymphatic vessels of the thoracic wall ramify beneath the skin and converge to the axillary glands. Those over the Trapezius and Latissimus dorsi run forward and unite to form about ten or twelve trunks which end in the subscapular group. Those over the pectoral region, including the vessels from the skin covering the peripheral part of the mamma, run backward, and those over the Serratus anterior upward, to the pectoral group. Others near the lateral margin of the sternum pass inward between the rib cartilages and end in the sternal glands, while the vessels of opposite sides anastomose across the front of the sternum. A few vessels from the upper part of the pectoral region ascend over the clavicle to the supraclavicular group of cervical glands.

  The Lymphatic Vessels of the Mamma originate in a plexus in the interlobular spaces and on the walls of the galactophorous ducts. Those from the central part of the gland pass to an intricate plexus situated beneath the areola, a plexus which receives also the lymphatics from the skin over the central part of the gland and those from the areola and nipple. Its efferents are collected into two trunks which pass to the pectoral group of axillary glands. The vessels which drain the medial part of the mamma pierce the thoracic wall and end in the sternal glands, while a vessel has occasionally been seen to emerge from the upper part of the mamma and, piercing the Pectoralis major, terminate in the subclavicular glands (607).

  The deep lymphatic vessels of the thoracic wall (621) consist of:

  1. The lymphatics of the muscles which lie on the ribs: most of these end in the axillary glands, but some from the Pectoralis major pass to the sternal glands. 2. The intercostal vessels which drain the Intercostales and parietal pleura. Those draining the Intercostales externi run backward and, after receiving the vessels which accompany the posterior branches of the intercostal arteries, end in the intercostal glands. Those of the Intercostales interni and parietal pleura consist of a single trunk in each space. These trunks run forward in the subpleural tissue and the upper six open separately into the sternal glands or into the vessels which unite them; those of the lower spaces unite to form a single trunk which terminates in the lowest of the sternal glands. 3. The lymphatic vessels of the diaphragm, which form two plexuses, one on its thoracic and another on its abdominal surface. These plexuses anastomose freely with each other, and are best marked on the parts covered respectively by the pleuræ and peritoneum. That on the thoracic surface communicates with the lymphatics of the costal and mediastinal parts of the pleura, and its efferents consist of three groups: (a) anterior, passing to the gland which lie near the junction of the seventh rib with its cartilage; (b) middle, to the glands on the esophagus and to those around the termination of the inferior vena cava; and (c) posterior, to the glands which surround the aorta at the point where this vessel leaves the thoracic cavity.

  The plexus on the abdominal surface is composed of fine vessels, and anastomoses with the lymphatics of the liver and, at the periphery of the diaphragm, with those of the subperitoneal tissue. The efferents from the right half of this plexus terminate partly in a group of glands on the trunk of the corresponding inferior phrenic artery, while others end in the right lateral aortic glands. Those from the left half of the plexus pass to the pre- and lateral aortic glands and to the glands on the terminal portion of the esophagus.

  The visceral lymphatic nodes consist of three groups, viz.: anterior mediastinal, posterior mediastinal, and tracheobronchial.

  The Anterior Mediastinal Glands (lymphoglandulæ mediastinales anteriores) are placed in the anterior part of the superior mediastinal cavity, in front of the aortic arch and in relation to the innominate veins and the large arterial trunks which arise from the aortic arch. They receive afferents from the thymus and pericardium, and from the sternal glands; their efferents unite with those of the tracheobronchial glands, to form the right and left bronchomediastinal trunks.

  The Posterior Mediastinal Glands (lymphoglandulæ mediastinales posteriores) lie behind the pericardium in relation to the esophagus and descending thoracic aorta. Their afferents are derived from the esophagus, the posterior part of the pericardium, the diaphragm, and the convex surface of the liver. Their efferents mostly end in the thoracic duct, but some join the tracheobronchial glands.

  

The Tracheobronchial Nodes (622) form four main groups: (a) tracheal, on either side of the trachea; (b) bronchial, in the angles between the lower part of the trachea and bronchi and in the angle between the two bronchi; (c) bronchopulmonary, in the hilus of each lung; and (d) pulmonary, in the lung substance, on the larger branches of the bronchi. The afferents of the tracheobronchial nodes drain the lungs and bronchi, the thoracic part of the trachea and the heart; some of the efferents of the posterior mediastinal nodes also end in this group. Their efferent vessels ascend upon the trachea and unite with efferents of the internal mammary and anterior mediastinal nodes to form the right and left bronchomediastinal trunks. The right bronchomediastinal trunk may join the right lymphatic duct, and the left the thoracic duct, but more frequently they open independently of these ducts into the junction of the internal jugular and subclavian veins of their own side.

  In all town dwellers there are continually being swept into these glands from the bronchi and alveoli large quantities of the dust and black carbonaceous pigment that are so freely inhaled in cities. At first the glands are moderately enlarged, firm, inky black, and gritty on section; later they enlarge still further, often becoming fibrous from the irritation set up by the minute foreign bodies with which they are crammed, and may break down into a soft slimy mass or may calcify.

 

  The lymphatic vessels of the thoracic viscera comprise those of the heart and pericardium, lungs and pleura, thymus, and esophagus.

 

  The Lymphatic Vessels of the Heart consist of two plexuses: (a) deep, immediately under the endocardium; and (b) superficial, subjacent to the visceral pericardium. The deep plexus opens into the superficial, the efferents of which form right and left collecting trunks. The left trunks, two or three in number, ascend in the anterior longitudinal sulcus, receiving, in their course, vessels from both ventricles. On reaching the coronary sulcus they are joined by a large trunk from the diaphragmatic surface of the heart, and then unite to form a single vessel which ascends between the pulmonary artery and the left atrium and ends in one of the tracheobronchial glands. The right trunk receives its afferents from the right atrium and from the right border and diaphragmatic surface of the right ventricle. It ascends in the posterior longitudinal sulcus and then runs forward in the coronary sulcus, and passes up behind the pulmonary artery, to end in one of the tracheobronchial glands.

  The Lymphatic Vessels of the Lungs originate in two plexuses, a superficial and a deep. The superficial plexus is placed beneath the pulmonary pleura. The deep accompanies the branches of the pulmonary vessels and the ramifications of the bronchi. In the case of the larger bronchi the deep plexus consists of two net-works—one, submucous, beneath the mucous membrane, and another, peribronchial, outside the walls of the bronchi. In the smaller bronchi there is but a single plexus, which extends as far as the bronchioles, but fails to reach the alveoli, in the walls of which there are no traces of lymphatic vessels. The superficial efferents turn around the borders of the lungs and the margins of their fissures, and converge to end in some glands situated at the hilus; the deep efferents are conducted to the hilus along the pulmonary vessels and bronchi, and end in the tracheobronchial nodes. Little or no anastomosis occurs between the superficial and deep lymphatics of the lungs, except in the region of the hilus.

  The Lymphatic Vessels of the Pleura consist of two sets—one in the visceral and another in the parietal part of the membrane. Those of the visceral pleura drain into the superficial efferents of the lung, while the lymphatics of the parietal pleura have three modes of ending, viz.: (a) those of the costal portion join the lymphatics of the Intercostales interni and so reach the sternal nodes; (b) those of the diaphragmatic part are drained by the efferents of the diaphragm; while (c) those of the mediastinal portion terminate in the posterior mediastinal nodes.

  The Lymphatic Vessels of the Thymus end in the anterior mediastinal, tracheobronchial, and sternal nodes.

  The Lymphatic Vessels of the Esophagus form a plexus around that tube, and the collecting vessels from the plexus drain into the posterior mediastinal nodes.

Lymphatic Trunks:

1) subclavian trunk (right and left); 2) jugular trunk (right and left); 3) bronchо-mediastinal trunk (right and left). They collect lymph from suitable half of head, neck, upper limbs, left or right half of thoracic cavity. These trunks fall into right venous angle or into left venous angle are these venous angles which are formed by subclavian vein and internal jugular vein. 4) lumbar trunk (right and left) collects lymph from lower limbs.

Lymphatic Ducts:

Thoracic duct forms in abdominal cavity on level of ХІІ thoracic - ІІ lumbar vertebrae by the confluence of right and left lumbar lymphatic trunks. There is triangular dilatation, the cisterna chyli or cistern of thoracic duct in this spot. Duct has abdominal part, thoracic part, cervical part and arch of thoracic duct. Last rounds a pleura cupola and ends by opening into the angle of junction of the left subclavian vein with the left internal jugular vein. In thoracic cavity a thoracic duct is situated in posterior mediastinum. It collects lymph from both lower limbs, abdominal, pelvic and left half of thoracic cavities.

The thoracic duct (ductus thoracicus) (599) conveys the greater part of the lymph and chyle into the blood. It is the common trunk of all the lymphatic vessels of the body, excepting those on the right side of the head, neck, and thorax, and right upper extremity, the right lung, right side of the heart, and the convex surface of the liver. In the adult it varies in length from 38 to 45 cm. and extends from the second lumbar vertebra to the root of the neck. It begins in the abdomen by a triangular dilatation, the cisterna chyli, which is situated on the front of the body of the second lumbar vertebra, to the right side of and behind the aorta, by the side of the right crus of the diaphragm. It enters the thorax through the aortic hiatus of the diaphragm, and ascends through the posterior mediastinal cavity between the aorta and azygos vein. Behind it in this region are the vertebral column, the right intercostal arteries, and the hemiazygos veins as they cross to open into the azygos vein; in front of it are the diaphragm, esophagus, and pericardium, the last being separated from it by a recess of the right pleural cavity. Opposite the fifth thoracic vertebra, it inclines toward the left side, enters the superior mediastinal cavity, and ascends behind the aortic arch and the thoracic part of the left subclavian artery and between the left side of the esophagus and the left pleura, to the upper orifice of the thorax. Passing into the neck it forms an arch which rises about 3 or 4 cm. above the clavicle and crosses anterior to the subclavian artery, the vertebral artery and vein, and the thyrocervical trunk or its branches. It also passes in front of the phrenic nerve and the medial border of the Scalenus anterior, but is separated from these two structures by the prevertebral fascia. In front of it are the left common carotid artery, vagus nerve, and internal jugular vein; it ends by opening into the angle of junction of the left subclavian vein with the left internal jugular vein. The thoracic duct, at its commencement, is about equal in diameter to a goose-quill, but it diminishes considerably in caliber in the middle of the thorax, and is again dilated just before its termination. It is generally flexuous, and constricted at intervals so as to present a varicose appearance. Not infrequently it divides in the middle of its course into two vessels of unequal size which soon reunite, or into several branches which form a plexiform interlacement. It occasionally divides at its upper part into two branches, right and left; the left ending in the usual manner, while the right opens into the right subclavian vein, in connection with the right lymphatic duct. The thoracic duct has several valves; at its termination it is provided with a pair, the free borders of which are turned toward the vein, so as to prevent the passage of venous blood into the duct.

  The cisterna chyli (receptaculum chyli) (600) receives the two lumbar lymphatic trunks, right and left, and the intestinal lymphatic trunk. The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymphatic nodes. They receive the lymph from the lower limbs, from the walls and viscera of the pelvis, from the kidneys and suprarenal glands and the deep lymphatics of the greater part of the abdominal wall. The intestinal trunk receives the lymph from the stomach and intestine, from the pancreas and spleen, and from the lower and front part of the liver.

 

Tributaries.—Opening into the commencement of the thoracic duct, on either side, is a descending trunk from the posterior intercostal lymphatic nodes of the lower six or seven intercostal spaces. In the thorax the duct is joined, on either side, by a trunk which drains the upper lumbar lymphatic nodes and pierces the crus of the diaphragm. It also receives the efferents from the posterior mediastinal lymphatic nodes and from the posterior intercostal lymphatic nodes of the upper six left spaces. In the neck it is joined by the left jugular and left subclavian trunks, and sometimes by the left bronchomediastinal trunk; the last-named, however, usually opens independently into the junction of the left subclavian and internal jugular veins.

The thoracic and right lymphatic ducts.

 

  The right lymphatic duct (ductus lymphaticus dexter) (601), about 1.25 cm. in length, courses along the medial border of the Scalenus anterior at the root of the neck and ends in the right subclavian vein, at its angle of junction with the right internal jugular vein. Its orifice is guarded by two semilunar valves, which prevent the passage of venous blood into the duct.

 

Tributaries.—The right lymphatic duct receives the lymph from the right side of the head and neck through the right jugular trunk; from the right upper extremity through the right subclavian trunk; from the right side of the thorax, right lung, right side of the heart, and part of the convex surface of the liver, through the right bronchomediastinal trunk. These three collecting trunks frequently open separately in the angle of union of the two veins.

Modes of origin of thoracic duct. (Poirier and Charpy.) a. Thoracic duct. a’. Cisterna chyli. b, c’ Efferent trunks from lateral aortic nodes. d. An efferent vessel which pierces the left crus of the diaphragm. e. f. Lateral aortic nodes. h. Retroaortic nodes. i. Intestinal trunk. j. Descending branch from intercostal lymphatics.

Terminal collecting trunks of right side. a. Jugular trunk. b. Subclavian trunk. c. Bronchomediastinal trunk. d. Right lymphatic trunk. e. Node of internal mammary chain. f. Node of deep cervical chain.

 

Right lymphatic duct is short, by length 10-12 mm, which is formed by confluence of right subclavian trunk, jugular trunk and bronchо-mediastinal trunk and runs into right venous angle. This duct transports lymph from right half of head, neck, right upper limb, right half of thoracic cavity. Frequently this duct can be absent, then the trunks independently fall into right venous angle or into terminal portion of thoracic duct.

 

 

 

Theme 2.     Thoracic part of sympathetic trunk and thoracic division of vagus. Intercostal nerves. Innervation of vicsera and walls of thorax

 

Thoracic ganglia of sympathetic trunk (10-12), which are contained near caput of ribs laterally from vertebral bodies. Thoracic ganglia receive the communicating white branches containing preganglionic fibers. Thoracic ganglia give off the following branches:

-         gray communicating branches, which approach to intercostal nerves;

-        

-         thoracic cardiac nerves being a party to forming of cardiac plexus;

-         thoracic pulmonary branches passing to bronchi and lungs, forming pulmonary plexus;

-         thoracic aortic rami, which form thoracic aortic plexus;

-         major splanchnic nerve, formed by branches from VI-IX thoracic ganglia and consist overwhelmingly of preganglionic fibers. This nerve passes through the lumbar part of diaphragm into abdominal cavity and terminates in ganglia of abdominal plexus;

-         minor splanchnic nerve starts from X-XI thoracic sympathetic ganglia and also has preganglionic fibers. It passes down into abdominal cavity (through the lumbar part of diaphragm) and enters into ganglia of abdominal plexus.

The thoracic portion of the sympathetic trunk (846).

 

 consists of a series of ganglia, which usually correspond in number to that of the vertebræ; but, on account of the occasional coalescence of two ganglia, their number is uncertain. The thoracic ganglia rest against the heads of the ribs, and are covered by the costal pleura; the last two, however, are more anterior than the rest, and are placed on the sides of the bodies of the eleventh and twelfth thoracic vertebræ. The ganglia are small in size, and of a grayish color. The first, larger than the others, is of an elongated form, and frequently blended with the inferior cervical ganglion. They are connected together by the intervening portions of the trunk.

  Two rami communicantes, a white and a gray, connect each ganglion with its corresponding spinal nerve.

  The branches from the upper five ganglia are very small; they supply filaments to the thoracic aorta and its branches. Twigs from the second, third, and fourth ganglia enter the posterior pulmonary plexus.

  The branches from the lower seven ganglia are large, and white in color; they distribute filaments to the aorta, and unite to form the greater, the lesser, and the lowest splanchnic nerves.

  

The greater splanchnic nerve (n. splanchnicus major; great splanchnic nerve) is white in color, firm in texture, and of a considerable size; it is formed by branches from the fifth to the ninth or tenth thoracic ganglia, but the fibers in the higher roots may be traced upward in the sympathetic trunk as far as the first or second thoracic ganglion. It descends obliquely on the bodies of the vertebræ, perforates the crus of the diaphragm, and ends in the celiac ganglion. A ganglion (ganglion splanchnicum) exists on this nerve opposite the eleventh or twelfth thoracic vertebra.

  

The lesser splanchnic nerve (n. splanchnicus minor) is formed by filaments from the ninth and tenth, and sometimes the eleventh thoracic ganglia, and from the cord between them. It pierces the diaphragm with the preceding nerve, and joins the aorticorenal ganglion.

  

The lowest splanchnic nerve (n. splanchnicus imus; least splanchnic nerve) arises from the last thoracic ganglion, and, piercing the diaphragm, ends in the renal plexus.

  A striking analogy exists between the splanchnic and the cardiac nerves. The cardiac nerves are three in number; they arise from all three cervical ganglia, and are distributed to a large and important organ in the thoracic cavity. The splanchnic nerves, also three in number, are connected probably with all the thoracic ganglia, and are distributed to important organs in the abdominal cavity.

Thoracic portion of the sympathetic trunk.

Parasympathetic part of X vagus nerve commences in dorsal nucleus of vagus nerve and contains a numerous of intramural ganglia. These ganglia enter to composition of cardiac, esophageal, pulmonary, gastric, intestinal, and others splanchnic plexus. Postganglionic neurons supply smooth muscles, glands and vessels of internal organs in neck, thoracic and abdominal regions.

*     Thoracic part of vagus nerve gives off:

Thoracic cardiac branches which pass to cardiac plexus;

Bronchial branches with sympathetic nerves form pulmonary plexus. Last enters in lungs with bronchi.

Esophageal branches form esophageal plexus round this organ.

The Inferior Cardiac Branches (rami cardiaci inferiores; thoracic cardiac branches), on the right side, arise from the trunk of the vagus as it lies by the side of the trachea, and from its recurrent nerve; on the left side from the recurrent nerve only; passing inward, they end in the deep part of the cardiac plexus.

  The Anterior Bronchial Branches (rami bronchiales anteriores; anterior or ventral pulmonary branches), two or three in number, and of small size, are distributed on the anterior surface of the root of the lung. They join with filaments from the sympathetic, and form the anterior pulmonary plexus.

  The Posterior Bronchial Branches (rami bronchiales posteriores; posterior or dorsal pulmonary branches), more numerous and larger than the anterior, are distributed on the posterior surface of the root of the lung; they are joined by filaments from the third and fourth (sometimes also from the first and second) thoracic ganglia of the sympathetic trunk, and form the posterior pulmonary plexus. Branches from this plexus accompany the ramifications of the bronchi through the substance of the lung.

  The Esophageal Branches (rami æsophagei) are given off both above and below the bronchial branches; the lower are numerous and larger than the upper. They form, together with the branches from the opposite nerve, the esophageal plexus. From this plexus filaments are distributed to the back of the pericardium.

Intercostal nerves

12 pairs of the ventral rami of the thoracic spinal nerves run between the ribs as intercostal nerves (the 12^th nerve called subcostal nerve). They pass in sulcus costae between the external and internal intercostal muscles and supply them, also the transverse thoracic muscle. Six upper intercostal nerves give off anterior and lateral cutaneous branches for skin in chest region, also medial (Th_II-IV) and lateral (Th_IV-VI) mammary branches for innervating the breast. Six lower intercostal nerves pass into hte depth of the abdominal muscles, into the sheath of the rectus abdominis muscle and supply muscles (*) and skin in anterior and lateral abdominal region (* - rectus abdominis, external, internal oblique and tranverse abdominis,  pyramidalis muscles).

The anterior divisions of the thoracic nerves (rami anteriores; ventral divisions) are twelve in number on either side. Eleven of them are situated between the ribs, and are therefore termed intercostal; the twelfth lies below the last rib. Each nerve is connected with the adjoining ganglion of the sympathetic trunk by a gray and a white ramus communicans. The intercostal nerves are distributed chiefly to the parietes of the thorax and abdomen, and differ from the anterior divisions of the other spinal nerves, in that each pursues an independent course, i. e., there is no plexus formation. The first two nerves supply fibers to the upper limb in addition to their thoracic branches; the next four are limited in their distribution to the parietes of the thorax; the lower five supply the parietes of the thorax and abdomen. The twelfth thoracic is distributed to the abdominal wall and the skin of the buttock.

 

The First Thoracic Nerve.—The anterior division of the first thoracic nerve divides into two branches: one, the larger, leaves the thorax in front of the neck of the first rib, and enters the brachial plexus; the other and smaller branch, the first intercostal nerve, runs along the first intercostal space, and ends on the front of the chest as the first anterior cutaneous branch of the thorax. Occasionally this anterior cutaneous branch is wanting. The first intercostal nerve as a rule gives off no lateral cutaneous branch; but sometimes it sends a small branch to communicate with the intercostobrachial. From the second thoracic nerve it frequently receives a connecting twig, which ascends over the neck of the second rib.

The Upper Thoracic Nerves (nn. intercostales).—The anterior divisions of the second, third, fourth, fifth, and sixth thoracic nerves, and the small branch from the first thoracic, are confined to the parietes of the thorax, and are named thoracic intercostal nerves. They pass forward (819) in the intercostal spaces below the intercostal vessels. At the back of the chest they lie between the pleura and the posterior intercostal membranes, but soon pierce the latter and run between the two planes of Intercostal muscles as far as the middle of the rib. They then enter the substance of the Intercostales interni, and, running amidst their fibers as far as the costal cartilages, they gain the inner surfaces of the muscles and lie between them and the pleura. Near the sternum, they cross in front of the internal mammary artery and Transversus thoracis muscle, pierce the Intercostales interni, the anterior intercostal membranes, and Pectoralis major, and supply the integument of the front of the thorax and over the mamma, forming the anterior cutaneous branches of the thorax; the branch from the second nerve unites with the anterior supraclavicular nerves of the cervical plexus.

 

Branches.—Numerous slender muscular filaments supply the Intercostales, the Subcostales, the Levatores costarum, the Serratus posterior superior, and the Transversus thoracis. At the front of the thorax some of these branches cross the costal cartilages from one intercostal space to another.

  Lateral cutaneous branches (rami cutanei laterales) are derived from the intercostal nerves, about midway between the vertebræ and sternum; they pierce the Intercostales externi and Serratus anterior, and divide into anterior and posterior branches. The anterior branches run forward to the side and the forepart of the chest, supplying the skin and the mamma; those of the fifth and sixth nerves supply the upper digitations of the Obliquus externus abdominis. The posterior branches run backward, and supply the skin over the scapula and Latissimus dorsi.   The lateral cutaneous branch of the second intercostal nerve does not divide, like the others, into an anterior and a posterior branch; it is named the intercostobrachial nerve (816). It pierces the Intercostalis externus and the Serratus anterior, crosses the axilla to the medial side of the arm, and joins with a filament from the medial brachial cutaneous nerve. It then pierces the fascia, and supplies the skin of the upper half of the medial and posterior part of the arm, communicating with the posterior brachial cutaneous branch of the radial nerve. The size of the intercostobrachial nerve is in inverse proportion to that of the medial brachial cutaneous nerve. A second intercostobrachial nerve is frequently given off from the lateral cutaneous branch of the third intercostal; it supplies filaments to the axilla and medial side of the arm.

Diagram of the course and branches of a typica intercostal nerve.

 

 

Cutaneous distribution of thoracic nerves.

 

Intercostal nerves, the superficial muscles having been removed. (Testut).

 

 

The Lower Thoracic Nerves.—The anterior divisions of the seventh, eighth, ninth, tenth, and eleventh thoracic nerves are continued anteriorly from the intercostal spaces into the abdominal wall; hence they are named thoracicoabdominal intercostal nerves. They have the same arrangement as the upper ones as far as the anterior ends of the intercostal spaces, where they pass behind the costal cartilages, and between the Obliquus internus and Transversus abdominis, to the sheath of the Rectus abdominis, which they perforate. They supply the Rectus abdominis and end as the anterior cutaneous branches of the abdomen; they supply the skin of the front of the abdomen. The lower intercostal nerves supply the Intercostales and abdominal muscles; the last three send branches to the Serratus posterior inferior. About the middle of their course they give off lateral cutaneous branches. These pierce the Intercostales externi and the Obliquus externus abdominis, in the same line as the lateral cutaneous branches of the upper thoracic nerves, and divide into anterior and posterior branches, which are distributed to the skin of the abdomen and back; the anterior branches supply the digitations of the Obliquus externus abdominis, and extend downward and forward nearly as far as the margin of the Rectus abdominis; the posterior branches pass backward to supply the skin over the Latissimus dorsi.

  The anterior division of the twelfth thoracic nerve is larger than the others; it runs along the lower border of the twelfth rib, often gives a communicating branch to the first lumbar nerve, and passes under the lateral lumbocostal arch. It then runs in front of the Quadratus lumborum, perforates the Transversus, and passes forward between it and the Obliquus internus to be distributed in the same manner as the lower intercostal nerves. It communicates with the iliohypogastric nerve of the lumbar plexus, and gives a branch to the Pyramidalis. The lateral cutaneous branch of the last thoracic nerve is large, and does not divide into an anterior and a posterior branch. It perforates the Obliqui internus and externus, descends over the iliac crest in front of the lateral cutaneous branch of the iliohypogastric (819), and is distributed to the skin of the front part of the gluteal region, some of its filaments extending as low as the greater trochanter.

VIDEO

Theme 3.     Abdominal aorta. Parietal  and visceral branches

Branches of abdominal part of aorta

They subdivide into parietal and visceral. The Visceral branches into its turn subdivide into pair and odd.

 

           The abdominal aorta (531) begins at the aortic hiatus of the diaphragm, in front of the lower border of the body of the last thoracic vertebra, and, descending in front of the vertebral column, ends on the body of the fourth lumbar vertebra, commonly a little to the left of the middle line, 103 by dividing into the two common iliac arteries. It diminishes rapidly in size, in consequence of the many large branches which it gives off. As it lies upon the bodies of the vertebræ, the curve which it describes is convex forward, the summit of the convexity corresponding to the third lumbar vertebra.

The abdominal aorta and its branches.

 

Relations.—The abdominal aorta is covered, anteriorly, by the lesser omentum and stomach, behind which are the branches of the celiac artery and the celiac plexus; below these, by the lienal vein, the pancreas, the left renal vein, the inferior part of the duodenum, the mesentery, and aortic plexus. Posteriorly, it is separated from the lumbar vertebræ and intervertebral fibrocartilages by the anterior longitudinal ligament and left lumbar veins. On the right side it is in relation above with the azygos vein, cisterna chyli, thoracic duct, and the right crus of the diaphragm—the last separating it from the upper part of the inferior vena cava, and from the right celiac ganglion; the inferior vena cava is in contact with the aorta below. On the left side are the left crus of the diaphragm, the left celiac ganglion, the ascending part of the duodenum, and some coils of the small intestine.

 

Collateral Circulation.—The collateral circulation would be carried on by the anastomoses between the internal mammary and the inferior epigastric; by the free communication between the superior and inferior mesenterics, if the ligature were placed between these vessels; or by the anastomosis between the inferior mesenteric and the internal pudendal, when (as is more common) the point of ligature is below the origin of the inferior mesenteric; and possibly by the anastomoses of the lumbar arteries with the branches of the hypogastric.

 

Branches.—The branches of the abdominal aorta may be divided into three sets: visceral, parietal, and terminal.

Visceral Branches.

Parietal Branches.

Celiac.

Inferior Phrenics.

Superior Mesenteric.

Lumbars.

Inferior Mesenteric.

Middle Sacral.

Middle Suprarenals.

Renals.

Internal Spermatics.

Terminal Branches.

Ovarian (in the female).

Common Iliacs.

  Of the visceral branches, the celiac artery and the superior and inferior mesenteric arteries are unpaired, while the suprarenals, renals, internal spermatics, and ovarian are paired. Of the parietal branches the inferior phrenics and lumbars are paired; the middle sacral is unpaired. The terminal branches are paired.

  The celiac artery (a. cæliaca; celiac axis) (532, 533) is a short thick trunk, about 1.25 cm. in length, which arises from the front of the aorta, just below the aortic hiatus of the diaphragm, and, passing nearly horizontally forward, divides into three large branches, the left gastric, the hepatic, and the splenic; it occasionally gives off one of the inferior phrenic arteries.

 

Relations.—The celiac artery is covered by the lesser omentum. On the right side it is in relation with the right celiac ganglion and the caudate process of the liver; on the left side, with the left celiac ganglion and the cardiac end of the stomach. Below, it is in relation to the upper border of the pancreas, and the lienal vein.

  1. The Left Gastric Artery (a. gastrica sinistra; gastric or coronary artery), the smallest of the three branches of the celiac artery, passes upward and to the left, posterior to the omental bursa, to the cardiac orifice of the stomach. Here it distributes branches to the esophagus, which anastomose with the aortic esophageal arteries; others supply the cardiac part of the stomach, anastomosing with branches of the lienal artery. It then runs from left to right, along the lesser curvature of the stomach to the pylorus, between the layers of the lesser omentum; it gives branches to both surfaces of the stomach and anastomoses with the right gastric artery.

  2. The Hepatic Artery (a. hepatica) in the adult is intermediate in size between the left gastric and lienal; in the fetus, it is the largest of the three branches of the celiac artery. It is first directed forward and to the right, to the upper margin of the superior part of the duodenum, forming the lower boundary of the epiploic foramen (foramen of Winslow). It then crosses the portal vein anteriorly and ascends between the layers of the lesser omentum, and in front of the epiploic foramen, to the porta hepatis, where it divides into two branches, right and left, which supply the corresponding lobes of the liver, accompanying the ramifications of the portal vein and hepatic ducts. The hepatic artery, in its course along the right border of the lesser omentum, is in relation with the common bile-duct and portal vein, the duct lying to the right of the artery, and the vein behind.

  Its branches are:

Right Gastric.

Gastroduodenal     

Right Gastroepiploic.

Superior Pancreaticoduodenal.

Cystic.

The celiac artery and its branches; the liver has been raised, and the lesser omentum and anterior layer of the greater omentum removed.

 

  The right gastric artery (a. gastrica dextra; pyloric artery) arises from the hepatic, above the pylorus, descends to the pyloric end of the stomach, and passes from right to left along its lesser curvature, supplying it with branches, and anastomosing with the left gastric artery.

  The gastroduodenal artery (a. gastroduodenalis) (533) is a short but large branch, which descends, near the pylorus, between the superior part of the duodenum and the neck of the pancreas, and divides at the lower border of the duodenum into two branches, the right gastroepiploic and the superior pancreaticoduodenal. Previous to its division it gives off two or three small branches to the pyloric end of the stomach and to the pancreas.

  The right gastroepiploic artery (a. gastroepiploica dextra) runs from right to left along the greater curvature of the stomach, between the layers of the greater omentum, anastomosing with the left gastroepiploic branch of the lienal artery. Except at the pylorus where it is in contact with the stomach, it lies about a finger's breadth from the greater curvature. This vessel gives off numerous branches, some of which ascend to supply both surfaces of the stomach, while others descend to supply the greater omentum and anastomose with branches of the middle colic.

  The superior pancreaticoduodenal artery (a. pancreaticoduodenalis superior) descends between the contiguous margins of the duodenum and pancreas. It supplies both these organs, and anastomoses with the inferior pancreaticoduodenal branch of the superior mesenteric artery, and with the pancreatic branches of the lienal artery.

The celiac artery and its branches; the stomach has been raised and the peritoneum removed.

 

 

  The cystic artery (a. cystica) (532), usually a branch of the right hepatic, passes downward and forward along the neck of the gall-bladder, and divides into two branches, one of which ramifies on the free surface, the other on the attached surface of the gall-bladder.

  3. The Lienal or Splenic Artery (a. lienalis), the largest branch of the celiac artery, is remarkable for the tortuosity of its course. It passes horizontally to the left side, behind the stomach and the omental bursa of the peritoneum, and along the upper border of the pancreas, accompanied by the lienal vein, which lies below it; it crosses in front of the upper part of the left kidney, and, on arriving near the spleen, divides into branches, some of which enter the hilus of that organ between the two layers of the phrenicolienal ligament to be distributed to the tissues of the spleen; some are given to the pancreas, while others pass to the greater curvature of the stomach between the layers of the gastrolienal ligament. Its branches are:

Pancreatic.

Short Gastric.

Left Gastroepiploic.

  The pancreatic branches (rami pancreatici) are numerous small vessels derived from the lienal as it runs behind the upper border of the pancreas, supplying its body and tail. One of these, larger than the rest, is sometimes given off near the tail of the pancreas; it runs from left to right near the posterior surface of the gland, following the course of the pancreatic duct, and is called the arteria pancreatica magna. These vessels anastomose with the pancreatic branches of the pancreaticoduodenal and superior mesenteric arteries.

 

  The short gastric arteries (aa. gastricæ breves; vasa brevia) consist of from five to seven small branches, which arise from the end of the lienal artery, and from its terminal divisions. They pass from left to right, between the layers of the gastrolienal ligament, and are distributed to the greater curvature of the stomach, anastomosing with branches of the left gastric and left gastroepiploic arteries.

  The left gastroepiploic artery (a. gastroepiploica sinistra) the largest branch of the lienal, runs from left to right about a finger’s breadth or more from the greater curvature of the stomach, between the layers of the greater omentum, and anastomoses with the right gastroepiploic. In its course it distributes several ascending branches to both surfaces of the stomach; others descend to supply the greater omentum and anastomose with branches of the middle colic.

  The superior mesenteric artery (a. mesenterica superior) (534) is a large vessel which supplies the whole length of the small intestine, except the superior part of the duodenum; it also supplies the cecum and the ascending part of the colon and about one-half of the transverse part of the colon. It arises from the front of the aorta, about 1.25 cm. below the celiac artery, and is crossed at its origin by the lienal vein and the neck of the pancreas. It passes downward and forward, anterior to the processus uncinatus of the head of the pancreas and inferior part of the duodenum, and descends between the layers of the mesentery to the right iliac fossa, where, considerably diminished in size, it anastomoses with one of its own branches, viz., the ileocolic. In its course it crosses in front of the inferior vena cava, the right ureter and Psoas major, and forms an arch, the convexity of which is directed foward and downward to the left side, the concavity backward and upward to the right. It is accompanied by the superior mesenteric vein, which lies to its right side, and it is surrounded by the superior mesenteric plexus of nerves.

 

Branches.—Its branches are:

Inferior Pancreaticoduodenal.

Ileocolic.

Intestinal.

Right Colic.

Middle Colic.

  The Inferior Pancreaticoduodenal Artery (a. pancreaticoduodenalis inferior) is given off from the superior mesenteric or from its first intestinal branch, opposite the upper border of the inferior part of the duodenum. It courses to the right between the head of the pancreas and duodenum, and then ascends to anastomose with the superior pancreaticoduodenal artery. It distributes branches to the head of the pancreas and to the descending and inferior parts of the duodenum.

  The Intestinal Arteries (aa. intestinales; vasa intestini tenuis) arise from the convex side of the superior mesenteric artery. They are usually from twelve to fifteen in number, and are distributed to the jejunum and ileum. They run nearly parallel with one another between the layers of the mesentery, each vessel dividing into two branches, which unite with adjacent branches, forming a series of arches, the convexities of which are directed toward the intestine (535). From this first set of arches branches arise, which unite with similar branches from above and below and thus a second series of arches is formed; from the lower branches of the artery, a third, a fourth, or even a fifth series of arches may be formed, diminishing in size the nearer they approach the intestine. In the short, upper part of the mesentery only one set of arches exists, but as the depth of the mesentery increases, second, third, fourth, or even fifth groups are developed. From the terminal arches numerous small straight vessels arise which encircle the intestine, upon which they are distributed, ramifying between its coats. From the intestinal arteries small branches are given off to the lymphatic nodes and other structures between the layers of the mesentery.

  The Ileocolic Artery (a. ileocolica) is the lowest branch arising from the concavity of the superior mesenteric artery. It passes downward and to the right behind the peritoneum toward the right iliac fossa, where it divides into a superior and an inferior branch; the inferior anastomoses with the end of the superior mesenteric artery, the superior with the right colic artery.

  The inferior branch of the ileocolic runs toward the upper border of the ileocolic junction and supplies the following branches (536):

  (a) colic, which pass upward on the ascending colon; (b) anterior and posterior cecal, which are distributed to the front and back of the cecum; (c) an appendicular artery, which descends behind the termination of the ileum and enters the mesenteriole of the vermiform process; it runs near the free margin of this mesenteriole and ends in branches which supply the vermiform process; and (d) ileal, which run upward and to the left on the lower part of the ileum, and anastomose with the termination of the superior mesenteric.

Loop of small intestine showing distribution of intestinal arteries

Arteries of cecum and vermiform process.

 

  The Right Colic Artery (a. colica dextra) arises from about the middle of the concavity of the superior mesenteric artery, or from a stem common to it and the ileocolic. It passes to the right behind the peritoneum, and in front of the right internal spermatic or ovarian vessels, the right ureter and the Psoas major, toward the middle of the ascending colon; sometimes the vessel lies at a higher level, and crosses the descending part of the duodenum and the lower end of the right kidney. At the colon it divides into a descending branch, which anastomoses with the ileocolic, and an ascending branch, which anastomoses with the middle colic. These branches form arches, from the convexity of which vessels are distributed to the ascending colon.

    The Middle Colic Artery (a. colica media) arises from the superior mesenteric just below the pancreas and, passing downward and forward between the layers of the transverse mesocolon, divides into two branches, right and left; the former anastomoses with the right colic; the latter with the left colic, a branch of the inferior mesenteric. The arches thus formed are placed about two fingers’ breadth from the transverse colon, to which they distribute branches.

  The inferior mesenteric artery (a. mesenterica inferior) (537) supplies the left half of the transverse part of the colon, the whole of the descending and iliac parts of the colon, the sigmoid colon, and the greater part of the rectum. It is smaller than the superior mesenteric, and arises from the aorta, about 3 or 4 cm. above its division into the common iliacs and close to the lower border of the inferior part of the duodenum. It passes downward posterior to the peritoneum, lying at first anterior to and then on the left side of the aorta. It crosses the left common iliac artery and is continued into the lesser pelvis under the name of the superior hemorrhoidal artery, which descends between the two layers of the sigmoid mesocolon and ends on the upper part of the rectum.

Branches.—Its branches are:

Left Colic.

Sigmoid.

Superior Hemorrhoidal.

The inferior mesenteric artery and its branches.

 

  The Left Colic Artery (a. colica sinistra) runs to the left behind the peritoneum and in front of the Psoas major, and after a short, but variable, course divides into an ascending and a descending branch; the stem of the artery or its branches cross the left ureter and left internal spermatic vessels. The ascending branch crosses in front of the left kidney and ends, between the two layers of the transverse mesocolon, by anastomosing with the middle colic artery; the descending branch anastomoses with the highest sigmoid artery. From the arches formed by these anastomoses branches are distributed to the descending colon and the left part of the transverse colon.

  The Sigmoid Arteries (aa. sigmoideæ) (538), two or three in number, run obliquely downward and to the left behind the peritoneum and in front of the Psoas major, ureter, and internal spermatic vessels. Their branches supply the lower part of the descending colon, the iliac colon, and the sigmoid or pelvic colon; anastomosing above with the left colic, and below with the superior hemorrhoidal artery.

  The Superior Hemorrhoidal Artery (a. hæmorrhoidalis superior) (538), the continuation of the inferior mesenteric, descends into the pelvis between the layers of the mesentery of the sigmoid colon, crossing, in its course, the left common iliac vessels. It divides, opposite the third sacral vertebra, into two branches, which descend one on either side of the rectum, and about 10 or 12 cm. from the anus break up into several small branches. These pierce the muscular coat of the bowel and run downward, as straight vessels, placed at regular intervals from each other in the wall of the gut between its muscular and mucous coats, to the level of the Sphincter ani internus; here they form a series of loops around the lower end of the rectum, and communicate with the middle hemorrhoidal branches of the hypogastric, and with the inferior hemorrhoidal branches of the internal pudendal.

  The middle suprarenal arteries (aa. suprarenales media; middle capsular arteries; suprarenal arteries) are two small vessels which arise, one from either side of the aorta, opposite the superior mesenteric artery. They pass lateralward and slightly upward, over the crura of the diaphragm, to the suprarenal glands, where they anastomose with suprarenal branches of the inferior phrenic and renal arteries. In the fetus these arteries are of large size.

  The renal arteries (aa. renales) (531), are two large trunks, which arise from the side of the aorta, immediately below the superior mesenteric artery. Each is directed across the crus of the diaphragm, so as to form nearly a right angle with the aorta. The right is longer than the left, on account of the position of the aorta; it passes behind the inferior vena cava, the right renal vein, the head of the pancreas, and the descending part of the duodenum. The left is somewhat higher than the right; it lies behind the left renal vein, the body of the pancreas and the lienal vein, and is crossed by the inferior mesenteric vein. Before reaching the hilus of the kidney, each artery divides into four or five branches; the greater number of these lie between the renal vein and ureter, the vein being in front, the ureter behind, but one or more branches are usually situated behind the ureter. Each vessel gives off some small inferior suprarenal branches to the suprarenal gland, the ureter, and the surrounding cellular tissue and muscles. One or two accessory renal arteries are frequently found, more especially on the left side they usually arise from the aorta, and may come off above or below the main artery, the former being the more common position. Instead of entering the kidney at the hilus, they usually pierce the upper or lower part of the gland.

  The internal spermatic arteries (aa. spermaticæ internæ; spermatic arteries) (531) are distributed to the testes. They are two slender vessels of considerable length, and arise from the front of the aorta a little below the renal arteries. Each passes obliquely downward and lateralward behind the peritoneum, resting on the Psoas major, the right spermatic lying in front of the inferior vena cava and behind the middle colic and ileocolic arteries and the terminal part of the ileum, the left behind the left colic and sigmoid arteries and the iliac colon. Each crosses obliquely over the ureter and the lower part of the external iliac artery to reach the abdominal inguinal ring, through which it passes, and accompanies the other constituents of the spermatic cord along the inguinal canal to the scrotum, where it becomes tortuous, and divides into several branches. Two or three of these accompany the ductus deferens, and supply the epididymis, anastomosing with the artery of the ductus deferens; others pierce the back part of the tunica albuginea, and supply the substance of the testis. The internal spermatic artery supplies one or two small branches to the ureter, and in the inguinal canal gives one or two twigs to the Cremaster.

Sigmoid colon and rectum, showing distribution of branches of inferior mesenteric artery and their anastomoses.

  The ovarian arteries (aa. ovaricæ) are the corresponding arteries in the female to the internal spermatic in the male. They supply the ovaries, are shorter than the internal spermatics, and do not pass out of the abdominal cavity. The origin and course of the first part of each artery are the same as those of the internal spermatic, but on arriving at the upper opening of the lesser pelvis the ovarian artery passes inward, between the two layers of the ovariopelvic ligament and of the broad ligament of the uterus, to be distributed to the ovary. Small branches are given to the ureter and the uterine tube, and one passes on to the side of the uterus, and unites with the uterine artery. Other offsets are continued on the round ligament of the uterus, through the inguinal canal, to the integument of the labium majus and groin.

  At an early period of fetal life, when the testes or ovaries lie by the side of the vertebral column, below the kidneys, the internal spermatic or ovarian arteries are short; but with the descent of these organs into the scrotum or lesser pelvis, the arteries are gradually lengthened.

  

  The inferior phrenic arteries (aa. phrenicæ inferiores) (531) are two small vessels, which supply the diaphragm but present much variety in their origin. They may arise separately from the front of the aorta, immediately above the celiac artery, or by a common trunk, which may spring either from the aorta or from the celiac artery. Sometimes one is derived from the aorta, and the other from one of the renal arteries; they rarely arise as separate vessels from the aorta. They diverge from one another across the crura of the diaphragm, and then run obliquely upward and lateralward upon its under surface. The left phrenic passes behind the esophagus, and runs forward on the left side of the esophageal hiatus. The right phrenic passes behind the inferior vena cava, and along the right side of the foramen which transmits that vein. Near the back part of the central tendon each vessel divides into a medial and a lateral branch. The medial branch curves forward, and anastomoses with its fellow of the opposite side, and with the musculophrenic and pericardiacophrenic arteries. The lateral branch passes toward the side of the thorax, and anastomoses with the lower intercostal arteries, and with the musculophrenic. The lateral branch of the right phrenic gives off a few vessels to the inferior vena cava; and the left one, some branches to the esophagus. Each vessel gives off superior suprarenal branches to the suprarenal gland of its own side. The spleen and the liver also receive a few twigs from the left and right vessels respectively.

  The lumbar arteries (aa. lumbales) are in series with the intercostals. They are usually four in number on either side, and arise from the back of the aorta, opposite the bodies of the upper four lumbar vertebræ. A fifth pair, small in size, is occasionally present: they arise from the middle sacral artery. They run lateralward and backward on the bodies of the lumbar vertebræ, behind the sympathetic trunk, to the intervals between the adjacent transverse processes, and are then continued into the abdominal wall. The arteries of the right side pass behind the inferior vena cava, and the upper two on each side run behind the corresponding crus of the diaphragm. The arteries of both sides pass beneath the tendinous arches which give origin to the Psoas major, and are then continued behind this muscle and the lumbar plexus. They now cross the Quadratus lumborum, the upper three arteries running behind, the last usually in front of the muscle. At the lateral border of the Quadratus lumborum they pierce the posterior aponeurosis of the Transversus abdominis and are carried forward between this muscle and the Obliquus internus. They anastomose with the lower intercostal, the subcostal, the iliolumbar, the deep iliac circumflex, and the inferior epigastric arteries.

The arteries of the pelvis.

 Branches.—In the interval between the adjacent transverse processes each lumbar artery gives off a posterior ramus which is continued backward between the transverse processes and is distributed to the muscles and skin of the back; it furnishes a spinal branch which enters the vertebral canal and is distributed in a manner similar to the spinal branches of the posterior rami of the intercostal arteries (page 601). Muscular branches are supplied from each lumbar artery and from its posterior ramus to the neighboring muscles.

  The middle sacral artery (a. sacralis media) (531) is a small vessel, which arises from the back of the aorta, a little above its bifurcation. It descends in the middle line in front of the fourth and fifth lumbar vertebræ, the sacrum and coccyx, and ends in the glomus coccygeum (coccygeal gland). From it, minute branches are said to pass to the posterior surface of the rectum. On the last lumbar vertebra it anastomoses with the lumbar branch of the iliolumbar artery; in front of the sacrum it anastomoses with the lateral sacral arteries, and sends offsets into the anterior sacral foramina. It is crossed by the left common iliac vein, and is accompanied by a pair of venæ comitantes; these unite to form a single vessel, which opens into the left common iliac vein.

Prepared by

Galytska-Harhalis O.Ya