Intercostal Arteries and Veins Each intercostal space contains a large single posterior intercostal artery and two small anterior intercostal arteries. The anterior intercostal arteries of the lower spaces are branches of THE MUSCULOPHRENIC ARTERY, one of the terminal branches of the internal thoracic artery. The posterior intercostal arteries of the first two spaces are branches from the superior intercostal artery, a branch of the costocervical trunk of the subclavian artery The posterior intercostal arteries of the lower nine spaces are branches of THE DESCENDING THORACIC AORTA The anterior intercostal arteries of the first six spaces are branches of THE INTERNAL THORACIC ARTERY which arises from the first part of the subclavian artery.
The corresponding posterior intercostal veins drain backward into the azygos or hemiazygos veins, and the anterior intercostal veins drain forward into the internal thoracic and musculophrenic veins
Intercostal Nerves The intercostal nerves are the anterior rami of the first 11 thoracic spinal nerves The anterior ramus of the 12th thoracic nerve lies in the abdomen and runs forward in the abdominal wall as the subcostal nerve
Each intercostal nerve enters an intercostal space between the parietal pleura and the posterior intercostal membrane It then runs forward inferiorly to the intercostal vessels in the subcostal groove of the corresponding rib, between the innermost intercostal and internal intercostal muscle.
The first six nerves are distributed within their intercostal spaces. The seventh to ninth intercostal nerves leave the anterior ends of their intercostal spaces by passing deep to the costal cartilages, to enter the anterior abdominal wall. The 10th and 11th nerves, since the corresponding ribs are floating, pass directly into the abdominal wall
CHEST CAVITY The chest cavity is bounded by the chest wall and below by the diaphragm It extends upward into the root of the neck about one fingerbreadth above the clavicle on each side The diaphragm, separates the chest from the abdominal viscera The chest cavity can be divided into MEDIAN PARTITION CALLED THE MEDIASTINUM LATERALLY PLACED PLEURAE AND LUNGS
The Mediastinum extends Superiorly: to the thoracic outlet and the root of the neck Inferiorly: to the diaphragm Anteriorly: to the sternum Posteriorly: to the vertebral column CONTENTS 1-THE REMAINS OF THE THYMUS 2-THE HEART 3- LARGE BLOOD VESSELS 4- THE TRACHEA 5-ESOPHAGUS 6-THE THORACIC DUCT AND LYMPH NODES 7-THE VAGUS AND PHRENIC NERVES 8-THE SYMPATHETIC TRUNKS
An imaginary plane passing from the sternal angle anteriorly to the lower border of the body of the fourth thoracic vertebra posteriorly divides the mediastinum into SUPERIOR AND INFERIOR MEDIASTINA
THE INFERIOR MEDIASTINUM is further subdivided into: 1-THE MIDDLE MEDIASTINUM consists of the pericardium and heart 2-THE ANTERIOR MEDIASTINUM is a space between the pericardium and the sternum 3-THE POSTERIOR MEDIASTINUM lies between THE PERICARDIUM And THE VERTEBRAL COLUMN
(a) THYMUS (b) LARGE VEINS (c) LARGE ARTERIES (d) TRACHEA (e) ESOPHAGUS (f) THORACIC DUCT (g) SYMPATHETIC TRUNKS THE SUPERIOR MEDIASTINUM is bounded in front by the manubrium sterni and behind by the first four thoracic vertebrae
THE INFERIOR MEDIASTINUM is bounded in front by the body of the sternum and behind by the lower eight thoracic vertebrae INFERIOR MEDIASTINUM (a) THYMUS (b) HEART WITHIN THE PERICARDIUM WITH THE PHRENIC NERVES ON EACH SIDE, (c) ESOPHAGUS AND THORACIC DUCT (d) DESCENDING AORTA (e) SYMPATHETIC TRUNKS
Pleurae The pleurae and lungs lie on either side of the mediastinum within the chest cavity FORMATION OF THE LUNGS Each lung bud invaginates the wall of the coelomic cavity and then grows to fill a greater part of the cavity the lung is covered with visceral pleura and the thoracic wall is lined with parietal pleura The original coelomic cavity is reduced to a slitlike space called the pleural cavity as a result of the growth of the lung.