awinml/medqa-textbooks-chunked · Datasets at Hugging Face

id stringlengths 14 28	file_name stringclasses 18 values	content stringlengths 1 722k
Anatomy_Gray_1100	Anatomy_Gray.txt	The joint between the second costal cartilage and the sternum is divided into two compartments by an intraarticular ligament. This ligament attaches the second costal cartilage to the junction of the manubrium and the body of the sternum.
Anatomy_Gray_1101	Anatomy_Gray.txt	Interchondral joints occur between the costal cartilages of adjacent ribs (Fig. 3.25), mainly between the costal cartilages of ribs VII to X, but may also involve the costal cartilages of ribs V and VI.
Anatomy_Gray_1102	Anatomy_Gray.txt	Interchondral joints provide indirect anchorage to the sternum and contribute to the formation of a smooth inferior costal margin. They are usually synovial, and the thin fibrous capsules are reinforced by interchondral ligaments.
Anatomy_Gray_1103	Anatomy_Gray.txt	The joints between the manubrium and the body of the sternum and between the body of the sternum and the xiphoid process are usually symphyses (Fig. 3.25). Only slight angular movements occur between the manubrium and the body of the sternum during respiration. The joint between the body of the sternum and the xiphoid process often becomes ossified with age.
Anatomy_Gray_1104	Anatomy_Gray.txt	A clinically useful feature of the manubriosternal joint is that it can be palpated easily. This is because the manubrium normally angles posteriorly on the body of the sternum, forming a raised feature referred to as the sternal angle. This elevation marks the site of articulation of rib II with the sternum. Rib I is not palpable, because it lies inferior to the clavicle and is embedded in tissues at the base of the neck. Therefore, rib II is used as a reference for counting ribs and can be felt immediately lateral to the sternal angle.
Anatomy_Gray_1105	Anatomy_Gray.txt	In addition, the sternal angle lies on a horizontal plane that passes through the intervertebral disc between vertebrae TIV and TV (see Fig. 3.10). This plane separates the superior mediastinum from the inferior mediastinum and marks the superior border of the pericardium. The plane also passes through the end of the ascending aorta and the beginning of the arch of the aorta, the end of the arch of the aorta and the beginning of the thoracic aorta, and the bifurcation of the trachea, and just superior to the pulmonary trunk (see Fig. 3.79 and 3.86).
Anatomy_Gray_1106	Anatomy_Gray.txt	Intercostal spaces lie between adjacent ribs and are filled by intercostal muscles (Fig. 3.26).
Anatomy_Gray_1107	Anatomy_Gray.txt	Intercostal nerves and associated major arteries and veins lie in the costal groove along the inferior margin of the superior rib and pass in the plane between the inner two layers of muscles.
Anatomy_Gray_1108	Anatomy_Gray.txt	In each space, the vein is the most superior structure and is therefore highest in the costal groove. The artery is inferior to the vein, and the nerve is inferior to the artery and often not protected by the groove. Therefore, the nerve is the structure most at risk when objects perforate the upper aspect of an intercostal space.
Anatomy_Gray_1109	Anatomy_Gray.txt	Small collateral branches of the major intercostal nerves and vessels are often present superior to the inferior rib below.
Anatomy_Gray_1110	Anatomy_Gray.txt	Deep to the intercostal spaces and ribs, and separating these structures from the underlying pleura, is a layer of loose connective tissue, called endothoracic fascia, which contains variable amounts of fat.
Anatomy_Gray_1111	Anatomy_Gray.txt	Superficial to the spaces are deep fascia, superficial fascia, and skin. Muscles associated with the upper limbs and back overlie the spaces.
Anatomy_Gray_1112	Anatomy_Gray.txt	Muscles of the thoracic wall include those that fill and support the intercostal spaces, those that pass between the sternum and the ribs, and those that cross several ribs between costal attachments (Table 3.2).
Anatomy_Gray_1113	Anatomy_Gray.txt	The muscles of the thoracic wall, together with muscles between the vertebrae and ribs posteriorly (i.e., the levatores costarum and serratus posterior superior and serratus posterior inferior muscles) alter the position of the ribs and sternum and so change the thoracic volume during breathing. They also reinforce the thoracic wall.
Anatomy_Gray_1114	Anatomy_Gray.txt	The intercostal muscles are three flat muscles found in each intercostal space that pass between adjacent ribs (Fig. 3.27). Individual muscles in this group are named according to their positions:
Anatomy_Gray_1115	Anatomy_Gray.txt	The external intercostal muscles are the most superficial.
Anatomy_Gray_1116	Anatomy_Gray.txt	The internal intercostal muscles are sandwiched between the external and innermost muscles.
Anatomy_Gray_1117	Anatomy_Gray.txt	The innermost intercostal muscles are the deepest of the three muscles.
Anatomy_Gray_1118	Anatomy_Gray.txt	The intercostal muscles are innervated by the related intercostal nerves. As a group, the intercostal muscles provide structural support for the intercostal spaces during breathing. They can also move the ribs.
Anatomy_Gray_1119	Anatomy_Gray.txt	The eleven pairs of external intercostal muscles extend from the inferior margins (lateral edges of costal grooves) of the ribs above to the superior margins of the ribs below. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely anteroinferiorly (Fig. 3.27). The muscles extend around the thoracic wall from the regions of the tubercles of the ribs to the costal cartilages, where each layer continues as a thin connective tissue aponeurosis termed the external intercostal membrane. The external intercostal muscles are most active in inspiration.
Anatomy_Gray_1120	Anatomy_Gray.txt	The eleven pairs of internal intercostal muscles pass between the most inferior lateral edge of the costal grooves of the ribs above, to the superior margins of the ribs below. They extend from parasternal regions, where the muscles course between adjacent costal cartilages, to the angle of the ribs posteriorly (Fig. 3.27). This layer continues medially toward the vertebral column, in each intercostal space, as the internal intercostal membrane. The muscle fibers pass in the opposite direction to those of the external intercostal muscles. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely posteroinferiorly. The internal intercostal muscles are most active during expiration.
Anatomy_Gray_1121	Anatomy_Gray.txt	The innermost intercostal muscles are the least distinct of the intercostal muscles, and the fibers have the same orientation as the internal intercostals (Fig. 3.27). These muscles are most evident in the lateral thoracic wall. They extend between the inner surfaces of adjacent ribs from the medial edge of the costal groove to the deep surface of the rib below. Importantly, the neurovascular bundles associated with the intercostal spaces pass around the thoracic wall in the costal grooves in a plane between the innermost and internal intercostal muscles.
Anatomy_Gray_1122	Anatomy_Gray.txt	The subcostales are in the same plane as the innermost intercostals, span multiple ribs, and are more numerous in lower regions of the posterior thoracic wall (Fig. 3.28A). They extend from the internal surfaces of one rib to the internal surface of the second (next) or third rib below. Their fibers parallel the course of the internal intercostal muscles and extend from the angle of the ribs to more medial positions on the ribs below.
Anatomy_Gray_1123	Anatomy_Gray.txt	The transversus thoracis muscles are found on the deep surface of the anterior thoracic wall (Fig. 3.28B) and in the same plane as the innermost intercostals.
Anatomy_Gray_1124	Anatomy_Gray.txt	The transversus thoracis muscles originate from the posterior aspect of the xiphoid process, the inferior part of the body of the sternum, and the adjacent costal cartilages of the lower true ribs. They pass superiorly and laterally to insert into the lower borders of the costal cartilages of ribs III to VI. They most likely pull these latter elements inferiorly.
Anatomy_Gray_1125	Anatomy_Gray.txt	The transversus thoracis muscles lie deep to the internal thoracic vessels and secure these vessels to the wall.
Anatomy_Gray_1126	Anatomy_Gray.txt	Vessels that supply the thoracic wall consist mainly of posterior and anterior intercostal arteries, which pass around the wall between adjacent ribs in intercostal spaces (Fig. 3.29). These arteries originate from the aorta and internal thoracic arteries, which in turn arise from the subclavian arteries in the root of the neck. Together, the intercostal arteries form a basket-like pattern of vascular supply around the thoracic wall.
Anatomy_Gray_1127	Anatomy_Gray.txt	Posterior intercostal arteries originate from vessels associated with the posterior thoracic wall. The upper two posterior intercostal arteries on each side are derived from the supreme intercostal artery, which descends into the thorax as a branch of the costocervical trunk in the neck. The costocervical trunk is a posterior branch of the subclavian artery (Fig. 3.29).
Anatomy_Gray_1128	Anatomy_Gray.txt	The remaining nine pairs of posterior intercostal arteries arise from the posterior surface of the thoracic aorta. Because the aorta is on the left side of the vertebral column, those posterior intercostal vessels passing to the right side of the thoracic wall cross the midline anterior to the bodies of the vertebrae and therefore are longer than the corresponding vessels on the left.
Anatomy_Gray_1129	Anatomy_Gray.txt	In addition to having numerous branches that supply various components of the wall, the posterior intercostal arteries have branches that accompany lateral cutaneous branches of the intercostal nerves to superficial regions.
Anatomy_Gray_1130	Anatomy_Gray.txt	The anterior intercostal arteries originate directly or indirectly as lateral branches from the internal thoracic arteries (Fig. 3.29).
Anatomy_Gray_1131	Anatomy_Gray.txt	Each internal thoracic artery arises as a major branch of the subclavian artery in the neck. It passes anteriorly over the cervical dome of the pleura and descends vertically through the superior thoracic aperture and along the deep aspect of the anterior thoracic wall. On each side, the internal thoracic artery lies posterior to the costal cartilages of the upper six ribs and about 1 cm lateral to the sternum. At approximately the level of the sixth intercostal space, it divides into two terminal branches: the superior epigastric artery, which continues inferiorly into the anterior abdominal wall (Fig. 3.29); and the musculophrenic artery, which passes along the costal margin, goes through the diaphragm, and ends near the last intercostal space.
Anatomy_Gray_1132	Anatomy_Gray.txt	Anterior intercostal arteries that supply the upper six intercostal spaces arise as lateral branches from the internal thoracic artery, whereas those supplying the lower spaces arise from the musculophrenic artery.
Anatomy_Gray_1133	Anatomy_Gray.txt	In each intercostal space, the anterior intercostal arteries usually have two branches:
Anatomy_Gray_1134	Anatomy_Gray.txt	One passes below the margin of the upper rib.
Anatomy_Gray_1135	Anatomy_Gray.txt	The other passes above the margin of the lower rib and meets a collateral branch of the posterior intercostal artery.
Anatomy_Gray_1136	Anatomy_Gray.txt	The distributions of the anterior and posterior intercostal vessels overlap and can develop anastomotic connections. The anterior intercostal arteries are generally smaller than the posterior vessels.
Anatomy_Gray_1137	Anatomy_Gray.txt	In addition to anterior intercostal arteries and a number of other branches, the internal thoracic arteries give rise to perforating branches that pass directly forward between the costal cartilages to supply structures external to the thoracic wall. These vessels travel with the anterior cutaneous branches of the intercostal nerves.
Anatomy_Gray_1138	Anatomy_Gray.txt	Venous drainage from the thoracic wall generally parallels the pattern of arterial supply (Fig. 3.30).
Anatomy_Gray_1139	Anatomy_Gray.txt	Centrally, the intercostal veins ultimately drain into the azygos system of veins or into internal thoracic veins, which connect with the brachiocephalic veins in the neck.
Anatomy_Gray_1140	Anatomy_Gray.txt	Often the upper posterior intercostal veins on the left side come together and form the left superior intercostal vein, which empties into the left brachiocephalic vein.
Anatomy_Gray_1141	Anatomy_Gray.txt	Similarly, the upper posterior intercostal veins on the right side may come together and form the right superior intercostal vein, which empties into the azygos vein.
Anatomy_Gray_1142	Anatomy_Gray.txt	Lymphatic vessels of the thoracic wall drain mainly into lymph nodes associated with the internal thoracic arteries (parasternal nodes), with the heads and necks of ribs (intercostal nodes), and with the diaphragm (diaphragmatic nodes) (Fig. 3.31). Diaphragmatic nodes are posterior to the xiphoid and at sites where the phrenic nerves penetrate the diaphragm. They also occur in regions where the diaphragm is attached to the vertebral column.
Anatomy_Gray_1143	Anatomy_Gray.txt	Parasternal nodes drain into bronchomediastinal trunks. Intercostal nodes in the upper thorax also drain into bronchomediastinal trunks, whereas intercostal nodes in the lower thorax drain into the thoracic duct.
Anatomy_Gray_1144	Anatomy_Gray.txt	Nodes associated with the diaphragm interconnect with parasternal, prevertebral, and juxta-esophageal nodes, brachiocephalic nodes (anterior to the brachiocephalic veins in the superior mediastinum), and lateral aortic/lumbar nodes (in the abdomen).
Anatomy_Gray_1145	Anatomy_Gray.txt	Superficial regions of the thoracic wall drain mainly into axillary lymph nodes in the axilla or parasternal nodes.
Anatomy_Gray_1146	Anatomy_Gray.txt	Innervation of the thoracic wall is mainly by the intercostal nerves, which are the anterior rami of spinal nerves T1 to T11 and lie in the intercostal spaces between adjacent ribs. The anterior ramus of spinal nerve T12 (the subcostal nerve) is inferior to rib XII (Fig. 3.32).
Anatomy_Gray_1147	Anatomy_Gray.txt	A typical intercostal nerve passes laterally around the thoracic wall in an intercostal space. The largest of the branches is the lateral cutaneous branch, which pierces the lateral thoracic wall and divides into an anterior branch and a posterior branch that innervate the overlying skin.
Anatomy_Gray_1148	Anatomy_Gray.txt	The intercostal nerves end as anterior cutaneous branches, which emerge either parasternally, between adjacent costal cartilages, or laterally to the midline, on the anterior abdominal wall, to supply the skin.
Anatomy_Gray_1149	Anatomy_Gray.txt	In addition to these major branches, small collateral branches can be found in the intercostal space running along the superior border of the lower rib.
Anatomy_Gray_1150	Anatomy_Gray.txt	In the thorax, the intercostal nerves carry: somatic motor innervation to the muscles of the thoracic wall (intercostal, subcostal, and transversus thoracis muscles), somatic sensory innervation from the skin and parietal pleura, and postganglionic sympathetic fibers to the periphery.
Anatomy_Gray_1151	Anatomy_Gray.txt	Sensory innervation of the skin overlying the upper thoracic wall is supplied by cutaneous branches (supraclavicular nerves), which descend from the cervical plexus in the neck.
Anatomy_Gray_1152	Anatomy_Gray.txt	In addition to innervating the thoracic wall, intercostal nerves innervate other regions:
Anatomy_Gray_1153	Anatomy_Gray.txt	The anterior ramus of T1 contributes to the brachial plexus.
Anatomy_Gray_1154	Anatomy_Gray.txt	The lateral cutaneous branch of the second intercostal nerve (the intercostobrachial nerve) contributes to cutaneous innervation of the medial surface of the upper arm.
Anatomy_Gray_1155	Anatomy_Gray.txt	The lower intercostal nerves supply the muscles, skin, and peritoneum of the abdominal wall.
Anatomy_Gray_1156	Anatomy_Gray.txt	The diaphragm is a thin musculotendinous structure that fills the inferior thoracic aperture and separates the thoracic cavity from the abdominal cavity (Fig. 3.34 and see Chapter 4). It is attached peripherally to the: xiphoid process of the sternum, costal margin of the thoracic wall, ends of ribs XI and XII, ligaments that span across structures of the posterior abdominal wall, and vertebrae of the lumbar region.
Anatomy_Gray_1157	Anatomy_Gray.txt	From these peripheral attachments, muscle fibers converge to join the central tendon. The pericardium is attached to the middle part of the central tendon.
Anatomy_Gray_1158	Anatomy_Gray.txt	In the median sagittal plane, the diaphragm slopes inferiorly from its anterior attachment to the xiphoid, approximately at vertebral level TVIII/IX, to its posterior attachment to the median arcuate ligament, crossing anteriorly to the aorta at approximately vertebral level TXII.
Anatomy_Gray_1159	Anatomy_Gray.txt	Structures traveling between the thorax and abdomen pass through the diaphragm or between the diaphragm and its peripheral attachments:
Anatomy_Gray_1160	Anatomy_Gray.txt	The inferior vena cava passes through the central tendon at approximately vertebral level TVIII.
Anatomy_Gray_1161	Anatomy_Gray.txt	The esophagus passes through the muscular part of the diaphragm, just to the left of midline, approximately at vertebral level TX.
Anatomy_Gray_1162	Anatomy_Gray.txt	The vagus nerves pass through the diaphragm with the esophagus.
Anatomy_Gray_1163	Anatomy_Gray.txt	The aorta passes behind the posterior attachment of the diaphragm at vertebral level TXII.
Anatomy_Gray_1164	Anatomy_Gray.txt	The thoracic duct passes behind the diaphragm with the aorta.
Anatomy_Gray_1165	Anatomy_Gray.txt	The azygos and hemiazygos veins may also pass through the aortic hiatus or through the crura of the diaphragm.
Anatomy_Gray_1166	Anatomy_Gray.txt	Other structures outside the posterior attachments of the diaphragm lateral to the aortic hiatus include the sympathetic trunks. The greater, lesser, and least splanchnic nerves penetrate the crura.
Anatomy_Gray_1167	Anatomy_Gray.txt	The arterial supply to the diaphragm is from vessels that arise superiorly and inferiorly to it (see Fig. 3.34). From above, pericardiacophrenic and musculophrenic arteries supply the diaphragm. These vessels are branches of the internal thoracic arteries. Superior phrenic arteries, which arise directly from lower parts of the thoracic aorta, and small branches from intercostal arteries contribute to the supply. The largest arteries supplying the diaphragm arise from below it. These arteries are the inferior phrenic arteries, which branch directly from the abdominal aorta.
Anatomy_Gray_1168	Anatomy_Gray.txt	Venous drainage of the diaphragm is by veins that generally parallel the arteries. The veins drain into: the brachiocephalic veins in the neck, the azygos system of veins, or abdominal veins (left suprarenal vein and inferior vena cava).
Anatomy_Gray_1169	Anatomy_Gray.txt	The diaphragm is innervated by the phrenic nerves (C3, C4, and C5), which penetrate the diaphragm and innervate it from its abdominal surface.
Anatomy_Gray_1170	Anatomy_Gray.txt	Contraction of the domes of the diaphragm flattens the diaphragm, thereby increasing thoracic volume. Movements of the diaphragm are essential for normal breathing.
Anatomy_Gray_1171	Anatomy_Gray.txt	One of the principal functions of the thoracic wall and the diaphragm is to alter the volume of the thorax and thereby move air in and out of the lungs.
Anatomy_Gray_1172	Anatomy_Gray.txt	During breathing, the dimensions of the thorax change in the vertical, lateral, and anteroposterior directions.
Anatomy_Gray_1173	Anatomy_Gray.txt	Elevation and depression of the diaphragm significantly alter the vertical dimensions of the thorax. Depression results when the muscle fibers of the diaphragm contract. Elevation occurs when the diaphragm relaxes.
Anatomy_Gray_1174	Anatomy_Gray.txt	Changes in the anteroposterior and lateral dimensions result from elevation and depression of the ribs (Fig. 3.35). The posterior ends of the ribs articulate with the vertebral column, whereas the anterior ends of most ribs articulate with the sternum or adjacent ribs.
Anatomy_Gray_1175	Anatomy_Gray.txt	Because the anterior ends of the ribs are inferior to the posterior ends, when the ribs are elevated, they move the sternum upward and forward. Also, the angle between the body of the sternum and the manubrium may become slightly less acute. When the ribs are depressed, the sternum moves downward and backward. This “pump handle” movement changes the dimensions of the thorax in the anteroposterior direction (Fig. 3.35A).
Anatomy_Gray_1176	Anatomy_Gray.txt	As well as the anterior ends of the ribs being lower than the posterior ends, the middles of the shafts tend to be lower than the two ends. When the shafts are elevated, the middles of the shafts move laterally. This “bucket handle” movement increases the lateral dimensions of the thorax (Fig. 3.35B).
Anatomy_Gray_1177	Anatomy_Gray.txt	Any muscles attaching to the ribs can potentially move one rib relative to another and therefore act as accessory respiratory muscles. Muscles in the neck and the abdomen can fix or alter the positions of upper and lower ribs.
Anatomy_Gray_1178	Anatomy_Gray.txt	Two pleural cavities, one on either side of the mediastinum, surround the lungs (Fig. 3.37):
Anatomy_Gray_1179	Anatomy_Gray.txt	Superiorly, they extend above rib I into the root of the neck.
Anatomy_Gray_1180	Anatomy_Gray.txt	Inferiorly, they extend to a level just above the costal margin.
Anatomy_Gray_1181	Anatomy_Gray.txt	The medial wall of each pleural cavity is the mediastinum.
Anatomy_Gray_1182	Anatomy_Gray.txt	Each pleural cavity is lined by a single layer of flat cells, mesothelium, and an associated layer of supporting connective tissue; together, they form the pleura.
Anatomy_Gray_1183	Anatomy_Gray.txt	The pleura is divided into two major types, based on location:
Anatomy_Gray_1184	Anatomy_Gray.txt	Pleura associated with the walls of a pleural cavity is parietal pleura (Fig. 3.37).
Anatomy_Gray_1185	Anatomy_Gray.txt	Pleura that reflects from the medial wall and onto the surface of the lung is visceral pleura (Fig. 3.37), which adheres to and covers the lung.
Anatomy_Gray_1186	Anatomy_Gray.txt	Each pleural cavity is the potential space enclosed between the visceral and parietal pleurae. They normally contain only a very thin layer of serous fluid. As a result, the surface of the lung, which is covered by visceral pleura, directly opposes and freely slides over the parietal pleura attached to the wall.
Anatomy_Gray_1187	Anatomy_Gray.txt	The names given to the parietal pleura correspond to the parts of the wall with which they are associated (Fig. 3.38):
Anatomy_Gray_1188	Anatomy_Gray.txt	Pleura related to the ribs and intercostal spaces is termed the costal part.
Anatomy_Gray_1189	Anatomy_Gray.txt	Pleura covering the diaphragm is the diaphragmatic part.
Anatomy_Gray_1190	Anatomy_Gray.txt	Pleura covering the mediastinum is the mediastinal part.
Anatomy_Gray_1191	Anatomy_Gray.txt	The dome-shaped layer of parietal pleura lining the cervical extension of the pleural cavity is cervical pleura (dome of pleura or pleural cupola).
Anatomy_Gray_1192	Anatomy_Gray.txt	Covering the superior surface of the cervical pleura is a distinct dome-like layer of fascia, the suprapleural membrane (Fig. 3.38). This connective tissue membrane is attached laterally to the medial margin of the first rib and behind to the transverse process of vertebra CVII. Superiorly, the membrane receives muscle fibers from some of the deep muscles in the neck (scalene muscles) that function to keep the membrane taut. The suprapleural membrane provides apical support for the pleural cavity in the root of the neck.
Anatomy_Gray_1193	Anatomy_Gray.txt	In the region of vertebrae TV to TVII, the mediastinal pleura reflects off the mediastinum as a tubular, sleeve-like covering for structures (i.e., airway, vessels, nerves, lymphatics) that pass between the lung and mediastinum. This sleeve-like covering and the structures it contains forms the root of the lung. The root joins the medial surface of the lung at an area referred to as the hilum of the lung. Here, the mediastinal pleura is continuous with the visceral pleura.
Anatomy_Gray_1194	Anatomy_Gray.txt	The parietal pleural is innervated by somatic afferent fibers. The costal pleura is innervated by branches from the intercostal nerves, and pain would be felt in relation to the thoracic wall. The diaphragmatic pleura and the mediastinal pleura are innervated mainly by the phrenic nerves (originating at spinal cord levels C3, C4, and C5). Pain from these areas would refer to the C3, C4, and C5 dermatomes (lateral neck and the supraclavicular region of the shoulder).
Anatomy_Gray_1195	Anatomy_Gray.txt	The peripheral reflections of parietal pleura mark the extent of the pleural cavities (Fig. 3.39).
Anatomy_Gray_1196	Anatomy_Gray.txt	Superiorly, the pleural cavity can project as much as 3 to 4 cm above the first costal cartilage but does not extend above the neck of rib I. This limitation is caused by the inferior slope of rib I to its articulation with the manubrium.
Anatomy_Gray_1197	Anatomy_Gray.txt	Anteriorly, the pleural cavities approach each other posterior to the upper part of the sternum. However, posterior to the lower part of the sternum, the parietal pleura does not come as close to the midline on the left side as it does on the right because the middle mediastinum, containing the pericardium and heart, bulges to the left.
Anatomy_Gray_1198	Anatomy_Gray.txt	Inferiorly, the costal pleura reflects onto the diaphragm above the costal margin. In the midclavicular line, the pleural cavity extends inferiorly to approximately rib VIII. In the midaxillary line, it extends to rib X. From this point, the inferior margin courses somewhat horizontally, crossing ribs XI and XII to reach vertebra TXII. From the midclavicular line to the vertebral column, the inferior boundary of the pleura can be approximated by a line that runs between rib VIII, rib X, and vertebra TXII.
Anatomy_Gray_1199	Anatomy_Gray.txt	The visceral pleura is continuous with the parietal pleura at the hilum of each lung, where structures enter and leave the organ. The visceral pleura is firmly attached to the surface of the lung, including both opposed surfaces of the fissures that divide the lungs into lobes.

Anatomy_Gray_1100

Anatomy_Gray.txt

The joint between the second costal cartilage and the sternum is divided into two compartments by an intraarticular ligament. This ligament attaches the second costal cartilage to the junction of the manubrium and the body of the sternum.

Anatomy_Gray_1101

Anatomy_Gray.txt

Interchondral joints occur between the costal cartilages of adjacent ribs (Fig. 3.25), mainly between the costal cartilages of ribs VII to X, but may also involve the costal cartilages of ribs V and VI.

Anatomy_Gray_1102

Anatomy_Gray.txt

Interchondral joints provide indirect anchorage to the sternum and contribute to the formation of a smooth inferior costal margin. They are usually synovial, and the thin fibrous capsules are reinforced by interchondral ligaments.

Anatomy_Gray_1103

Anatomy_Gray.txt

The joints between the manubrium and the body of the sternum and between the body of the sternum and the xiphoid process are usually symphyses (Fig. 3.25). Only slight angular movements occur between the manubrium and the body of the sternum during respiration. The joint between the body of the sternum and the xiphoid process often becomes ossified with age.

Anatomy_Gray_1104

Anatomy_Gray.txt

A clinically useful feature of the manubriosternal joint is that it can be palpated easily. This is because the manubrium normally angles posteriorly on the body of the sternum, forming a raised feature referred to as the sternal angle. This elevation marks the site of articulation of rib II with the sternum. Rib I is not palpable, because it lies inferior to the clavicle and is embedded in tissues at the base of the neck. Therefore, rib II is used as a reference for counting ribs and can be felt immediately lateral to the sternal angle.

Anatomy_Gray_1105

Anatomy_Gray.txt

In addition, the sternal angle lies on a horizontal plane that passes through the intervertebral disc between vertebrae TIV and TV (see Fig. 3.10). This plane separates the superior mediastinum from the inferior mediastinum and marks the superior border of the pericardium. The plane also passes through the end of the ascending aorta and the beginning of the arch of the aorta, the end of the arch of the aorta and the beginning of the thoracic aorta, and the bifurcation of the trachea, and just superior to the pulmonary trunk (see Fig. 3.79 and 3.86).

Anatomy_Gray_1106

Anatomy_Gray.txt

Intercostal spaces lie between adjacent ribs and are filled by intercostal muscles (Fig. 3.26).

Anatomy_Gray_1107

Anatomy_Gray.txt

Intercostal nerves and associated major arteries and veins lie in the costal groove along the inferior margin of the superior rib and pass in the plane between the inner two layers of muscles.

Anatomy_Gray_1108

Anatomy_Gray.txt

In each space, the vein is the most superior structure and is therefore highest in the costal groove. The artery is inferior to the vein, and the nerve is inferior to the artery and often not protected by the groove. Therefore, the nerve is the structure most at risk when objects perforate the upper aspect of an intercostal space.

Anatomy_Gray_1109

Anatomy_Gray.txt

Small collateral branches of the major intercostal nerves and vessels are often present superior to the inferior rib below.

Anatomy_Gray_1110

Anatomy_Gray.txt

Deep to the intercostal spaces and ribs, and separating these structures from the underlying pleura, is a layer of loose connective tissue, called endothoracic fascia, which contains variable amounts of fat.

Anatomy_Gray_1111

Anatomy_Gray.txt

Superficial to the spaces are deep fascia, superficial fascia, and skin. Muscles associated with the upper limbs and back overlie the spaces.

Anatomy_Gray_1112

Anatomy_Gray.txt

Muscles of the thoracic wall include those that fill and support the intercostal spaces, those that pass between the sternum and the ribs, and those that cross several ribs between costal attachments (Table 3.2).

Anatomy_Gray_1113

Anatomy_Gray.txt

The muscles of the thoracic wall, together with muscles between the vertebrae and ribs posteriorly (i.e., the levatores costarum and serratus posterior superior and serratus posterior inferior muscles) alter the position of the ribs and sternum and so change the thoracic volume during breathing. They also reinforce the thoracic wall.

Anatomy_Gray_1114

Anatomy_Gray.txt

The intercostal muscles are three flat muscles found in each intercostal space that pass between adjacent ribs (Fig. 3.27). Individual muscles in this group are named according to their positions:

Anatomy_Gray_1115

Anatomy_Gray.txt

The external intercostal muscles are the most superficial.

Anatomy_Gray_1116

Anatomy_Gray.txt

The internal intercostal muscles are sandwiched between the external and innermost muscles.

Anatomy_Gray_1117

Anatomy_Gray.txt

The innermost intercostal muscles are the deepest of the three muscles.

Anatomy_Gray_1118

Anatomy_Gray.txt

The intercostal muscles are innervated by the related intercostal nerves. As a group, the intercostal muscles provide structural support for the intercostal spaces during breathing. They can also move the ribs.

Anatomy_Gray_1119

Anatomy_Gray.txt

The eleven pairs of external intercostal muscles extend from the inferior margins (lateral edges of costal grooves) of the ribs above to the superior margins of the ribs below. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely anteroinferiorly (Fig. 3.27). The muscles extend around the thoracic wall from the regions of the tubercles of the ribs to the costal cartilages, where each layer continues as a thin connective tissue aponeurosis termed the external intercostal membrane. The external intercostal muscles are most active in inspiration.

Anatomy_Gray_1120

Anatomy_Gray.txt

The eleven pairs of internal intercostal muscles pass between the most inferior lateral edge of the costal grooves of the ribs above, to the superior margins of the ribs below. They extend from parasternal regions, where the muscles course between adjacent costal cartilages, to the angle of the ribs posteriorly (Fig. 3.27). This layer continues medially toward the vertebral column, in each intercostal space, as the internal intercostal membrane. The muscle fibers pass in the opposite direction to those of the external intercostal muscles. When the thoracic wall is viewed from a lateral position, the muscle fibers pass obliquely posteroinferiorly. The internal intercostal muscles are most active during expiration.

Anatomy_Gray_1121

Anatomy_Gray.txt

The innermost intercostal muscles are the least distinct of the intercostal muscles, and the fibers have the same orientation as the internal intercostals (Fig. 3.27). These muscles are most evident in the lateral thoracic wall. They extend between the inner surfaces of adjacent ribs from the medial edge of the costal groove to the deep surface of the rib below. Importantly, the neurovascular bundles associated with the intercostal spaces pass around the thoracic wall in the costal grooves in a plane between the innermost and internal intercostal muscles.

Anatomy_Gray_1122

Anatomy_Gray.txt

The subcostales are in the same plane as the innermost intercostals, span multiple ribs, and are more numerous in lower regions of the posterior thoracic wall (Fig. 3.28A). They extend from the internal surfaces of one rib to the internal surface of the second (next) or third rib below. Their fibers parallel the course of the internal intercostal muscles and extend from the angle of the ribs to more medial positions on the ribs below.

Anatomy_Gray_1123

Anatomy_Gray.txt

The transversus thoracis muscles are found on the deep surface of the anterior thoracic wall (Fig. 3.28B) and in the same plane as the innermost intercostals.

Anatomy_Gray_1124

Anatomy_Gray.txt

The transversus thoracis muscles originate from the posterior aspect of the xiphoid process, the inferior part of the body of the sternum, and the adjacent costal cartilages of the lower true ribs. They pass superiorly and laterally to insert into the lower borders of the costal cartilages of ribs III to VI. They most likely pull these latter elements inferiorly.

Anatomy_Gray_1125

Anatomy_Gray.txt

The transversus thoracis muscles lie deep to the internal thoracic vessels and secure these vessels to the wall.

Anatomy_Gray_1126

Anatomy_Gray.txt

Vessels that supply the thoracic wall consist mainly of posterior and anterior intercostal arteries, which pass around the wall between adjacent ribs in intercostal spaces (Fig. 3.29). These arteries originate from the aorta and internal thoracic arteries, which in turn arise from the subclavian arteries in the root of the neck. Together, the intercostal arteries form a basket-like pattern of vascular supply around the thoracic wall.

Anatomy_Gray_1127

Anatomy_Gray.txt

Posterior intercostal arteries originate from vessels associated with the posterior thoracic wall. The upper two posterior intercostal arteries on each side are derived from the supreme intercostal artery, which descends into the thorax as a branch of the costocervical trunk in the neck. The costocervical trunk is a posterior branch of the subclavian artery (Fig. 3.29).

Anatomy_Gray_1128

Anatomy_Gray.txt

The remaining nine pairs of posterior intercostal arteries arise from the posterior surface of the thoracic aorta. Because the aorta is on the left side of the vertebral column, those posterior intercostal vessels passing to the right side of the thoracic wall cross the midline anterior to the bodies of the vertebrae and therefore are longer than the corresponding vessels on the left.

Anatomy_Gray_1129

Anatomy_Gray.txt

In addition to having numerous branches that supply various components of the wall, the posterior intercostal arteries have branches that accompany lateral cutaneous branches of the intercostal nerves to superficial regions.

Anatomy_Gray_1130

Anatomy_Gray.txt

The anterior intercostal arteries originate directly or indirectly as lateral branches from the internal thoracic arteries (Fig. 3.29).

Anatomy_Gray_1131

Anatomy_Gray.txt

Each internal thoracic artery arises as a major branch of the subclavian artery in the neck. It passes anteriorly over the cervical dome of the pleura and descends vertically through the superior thoracic aperture and along the deep aspect of the anterior thoracic wall. On each side, the internal thoracic artery lies posterior to the costal cartilages of the upper six ribs and about 1 cm lateral to the sternum. At approximately the level of the sixth intercostal space, it divides into two terminal branches: the superior epigastric artery, which continues inferiorly into the anterior abdominal wall (Fig. 3.29); and the musculophrenic artery, which passes along the costal margin, goes through the diaphragm, and ends near the last intercostal space.

Anatomy_Gray_1132

Anatomy_Gray.txt

Anterior intercostal arteries that supply the upper six intercostal spaces arise as lateral branches from the internal thoracic artery, whereas those supplying the lower spaces arise from the musculophrenic artery.

Anatomy_Gray_1133

Anatomy_Gray.txt

In each intercostal space, the anterior intercostal arteries usually have two branches:

Anatomy_Gray_1134

Anatomy_Gray.txt

One passes below the margin of the upper rib.

Anatomy_Gray_1135

Anatomy_Gray.txt

The other passes above the margin of the lower rib and meets a collateral branch of the posterior intercostal artery.

Anatomy_Gray_1136

Anatomy_Gray.txt

The distributions of the anterior and posterior intercostal vessels overlap and can develop anastomotic connections. The anterior intercostal arteries are generally smaller than the posterior vessels.

Anatomy_Gray_1137

Anatomy_Gray.txt

In addition to anterior intercostal arteries and a number of other branches, the internal thoracic arteries give rise to perforating branches that pass directly forward between the costal cartilages to supply structures external to the thoracic wall. These vessels travel with the anterior cutaneous branches of the intercostal nerves.

Anatomy_Gray_1138

Anatomy_Gray.txt

Venous drainage from the thoracic wall generally parallels the pattern of arterial supply (Fig. 3.30).

Anatomy_Gray_1139

Anatomy_Gray.txt

Centrally, the intercostal veins ultimately drain into the azygos system of veins or into internal thoracic veins, which connect with the brachiocephalic veins in the neck.

Anatomy_Gray_1140

Anatomy_Gray.txt

Often the upper posterior intercostal veins on the left side come together and form the left superior intercostal vein, which empties into the left brachiocephalic vein.

Anatomy_Gray_1141

Anatomy_Gray.txt

Similarly, the upper posterior intercostal veins on the right side may come together and form the right superior intercostal vein, which empties into the azygos vein.

Anatomy_Gray_1142

Anatomy_Gray.txt

Lymphatic vessels of the thoracic wall drain mainly into lymph nodes associated with the internal thoracic arteries (parasternal nodes), with the heads and necks of ribs (intercostal nodes), and with the diaphragm (diaphragmatic nodes) (Fig. 3.31). Diaphragmatic nodes are posterior to the xiphoid and at sites where the phrenic nerves penetrate the diaphragm. They also occur in regions where the diaphragm is attached to the vertebral column.

Anatomy_Gray_1143

Anatomy_Gray.txt

Parasternal nodes drain into bronchomediastinal trunks. Intercostal nodes in the upper thorax also drain into bronchomediastinal trunks, whereas intercostal nodes in the lower thorax drain into the thoracic duct.

Anatomy_Gray_1144

Anatomy_Gray.txt

Nodes associated with the diaphragm interconnect with parasternal, prevertebral, and juxta-esophageal nodes, brachiocephalic nodes (anterior to the brachiocephalic veins in the superior mediastinum), and lateral aortic/lumbar nodes (in the abdomen).

Anatomy_Gray_1145

Anatomy_Gray.txt

Superficial regions of the thoracic wall drain mainly into axillary lymph nodes in the axilla or parasternal nodes.

Anatomy_Gray_1146

Anatomy_Gray.txt

Innervation of the thoracic wall is mainly by the intercostal nerves, which are the anterior rami of spinal nerves T1 to T11 and lie in the intercostal spaces between adjacent ribs. The anterior ramus of spinal nerve T12 (the subcostal nerve) is inferior to rib XII (Fig. 3.32).

Anatomy_Gray_1147

Anatomy_Gray.txt

A typical intercostal nerve passes laterally around the thoracic wall in an intercostal space. The largest of the branches is the lateral cutaneous branch, which pierces the lateral thoracic wall and divides into an anterior branch and a posterior branch that innervate the overlying skin.

Anatomy_Gray_1148

Anatomy_Gray.txt

The intercostal nerves end as anterior cutaneous branches, which emerge either parasternally, between adjacent costal cartilages, or laterally to the midline, on the anterior abdominal wall, to supply the skin.

Anatomy_Gray_1149

Anatomy_Gray.txt

In addition to these major branches, small collateral branches can be found in the intercostal space running along the superior border of the lower rib.

Anatomy_Gray_1150

Anatomy_Gray.txt

In the thorax, the intercostal nerves carry: somatic motor innervation to the muscles of the thoracic wall (intercostal, subcostal, and transversus thoracis muscles), somatic sensory innervation from the skin and parietal pleura, and postganglionic sympathetic fibers to the periphery.

Anatomy_Gray_1151

Anatomy_Gray.txt

Sensory innervation of the skin overlying the upper thoracic wall is supplied by cutaneous branches (supraclavicular nerves), which descend from the cervical plexus in the neck.

Anatomy_Gray_1152

Anatomy_Gray.txt

In addition to innervating the thoracic wall, intercostal nerves innervate other regions:

Anatomy_Gray_1153

Anatomy_Gray.txt

The anterior ramus of T1 contributes to the brachial plexus.

Anatomy_Gray_1154

Anatomy_Gray.txt

The lateral cutaneous branch of the second intercostal nerve (the intercostobrachial nerve) contributes to cutaneous innervation of the medial surface of the upper arm.

Anatomy_Gray_1155

Anatomy_Gray.txt

The lower intercostal nerves supply the muscles, skin, and peritoneum of the abdominal wall.

Anatomy_Gray_1156

Anatomy_Gray.txt

The diaphragm is a thin musculotendinous structure that fills the inferior thoracic aperture and separates the thoracic cavity from the abdominal cavity (Fig. 3.34 and see Chapter 4). It is attached peripherally to the: xiphoid process of the sternum, costal margin of the thoracic wall, ends of ribs XI and XII, ligaments that span across structures of the posterior abdominal wall, and vertebrae of the lumbar region.

Anatomy_Gray_1157

Anatomy_Gray.txt

From these peripheral attachments, muscle fibers converge to join the central tendon. The pericardium is attached to the middle part of the central tendon.

Anatomy_Gray_1158

Anatomy_Gray.txt

In the median sagittal plane, the diaphragm slopes inferiorly from its anterior attachment to the xiphoid, approximately at vertebral level TVIII/IX, to its posterior attachment to the median arcuate ligament, crossing anteriorly to the aorta at approximately vertebral level TXII.

Anatomy_Gray_1159

Anatomy_Gray.txt

Structures traveling between the thorax and abdomen pass through the diaphragm or between the diaphragm and its peripheral attachments:

Anatomy_Gray_1160

Anatomy_Gray.txt

The inferior vena cava passes through the central tendon at approximately vertebral level TVIII.

Anatomy_Gray_1161

Anatomy_Gray.txt

The esophagus passes through the muscular part of the diaphragm, just to the left of midline, approximately at vertebral level TX.

Anatomy_Gray_1162

Anatomy_Gray.txt

The vagus nerves pass through the diaphragm with the esophagus.

Anatomy_Gray_1163

Anatomy_Gray.txt

The aorta passes behind the posterior attachment of the diaphragm at vertebral level TXII.

Anatomy_Gray_1164

Anatomy_Gray.txt

The thoracic duct passes behind the diaphragm with the aorta.

Anatomy_Gray_1165

Anatomy_Gray.txt

The azygos and hemiazygos veins may also pass through the aortic hiatus or through the crura of the diaphragm.

Anatomy_Gray_1166

Anatomy_Gray.txt

Other structures outside the posterior attachments of the diaphragm lateral to the aortic hiatus include the sympathetic trunks. The greater, lesser, and least splanchnic nerves penetrate the crura.

Anatomy_Gray_1167

Anatomy_Gray.txt

The arterial supply to the diaphragm is from vessels that arise superiorly and inferiorly to it (see Fig. 3.34). From above, pericardiacophrenic and musculophrenic arteries supply the diaphragm. These vessels are branches of the internal thoracic arteries. Superior phrenic arteries, which arise directly from lower parts of the thoracic aorta, and small branches from intercostal arteries contribute to the supply. The largest arteries supplying the diaphragm arise from below it. These arteries are the inferior phrenic arteries, which branch directly from the abdominal aorta.

Anatomy_Gray_1168

Anatomy_Gray.txt

Venous drainage of the diaphragm is by veins that generally parallel the arteries. The veins drain into: the brachiocephalic veins in the neck, the azygos system of veins, or abdominal veins (left suprarenal vein and inferior vena cava).

Anatomy_Gray_1169

Anatomy_Gray.txt

The diaphragm is innervated by the phrenic nerves (C3, C4, and C5), which penetrate the diaphragm and innervate it from its abdominal surface.

Anatomy_Gray_1170

Anatomy_Gray.txt

Contraction of the domes of the diaphragm flattens the diaphragm, thereby increasing thoracic volume. Movements of the diaphragm are essential for normal breathing.

Anatomy_Gray_1171

Anatomy_Gray.txt

One of the principal functions of the thoracic wall and the diaphragm is to alter the volume of the thorax and thereby move air in and out of the lungs.

Anatomy_Gray_1172

Anatomy_Gray.txt

During breathing, the dimensions of the thorax change in the vertical, lateral, and anteroposterior directions.

Anatomy_Gray_1173

Anatomy_Gray.txt

Elevation and depression of the diaphragm significantly alter the vertical dimensions of the thorax. Depression results when the muscle fibers of the diaphragm contract. Elevation occurs when the diaphragm relaxes.

Anatomy_Gray_1174

Anatomy_Gray.txt

Changes in the anteroposterior and lateral dimensions result from elevation and depression of the ribs (Fig. 3.35). The posterior ends of the ribs articulate with the vertebral column, whereas the anterior ends of most ribs articulate with the sternum or adjacent ribs.

Anatomy_Gray_1175

Anatomy_Gray.txt

Because the anterior ends of the ribs are inferior to the posterior ends, when the ribs are elevated, they move the sternum upward and forward. Also, the angle between the body of the sternum and the manubrium may become slightly less acute. When the ribs are depressed, the sternum moves downward and backward. This “pump handle” movement changes the dimensions of the thorax in the anteroposterior direction (Fig. 3.35A).

Anatomy_Gray_1176

Anatomy_Gray.txt

As well as the anterior ends of the ribs being lower than the posterior ends, the middles of the shafts tend to be lower than the two ends. When the shafts are elevated, the middles of the shafts move laterally. This “bucket handle” movement increases the lateral dimensions of the thorax (Fig. 3.35B).

Anatomy_Gray_1177

Anatomy_Gray.txt

Any muscles attaching to the ribs can potentially move one rib relative to another and therefore act as accessory respiratory muscles. Muscles in the neck and the abdomen can fix or alter the positions of upper and lower ribs.

Anatomy_Gray_1178

Anatomy_Gray.txt

Two pleural cavities, one on either side of the mediastinum, surround the lungs (Fig. 3.37):

Anatomy_Gray_1179

Anatomy_Gray.txt

Superiorly, they extend above rib I into the root of the neck.

Anatomy_Gray_1180

Anatomy_Gray.txt

Inferiorly, they extend to a level just above the costal margin.

Anatomy_Gray_1181

Anatomy_Gray.txt

The medial wall of each pleural cavity is the mediastinum.

Anatomy_Gray_1182

Anatomy_Gray.txt

Each pleural cavity is lined by a single layer of flat cells, mesothelium, and an associated layer of supporting connective tissue; together, they form the pleura.

Anatomy_Gray_1183

Anatomy_Gray.txt

The pleura is divided into two major types, based on location:

Anatomy_Gray_1184

Anatomy_Gray.txt

Pleura associated with the walls of a pleural cavity is parietal pleura (Fig. 3.37).

Anatomy_Gray_1185

Anatomy_Gray.txt

Pleura that reflects from the medial wall and onto the surface of the lung is visceral pleura (Fig. 3.37), which adheres to and covers the lung.

Anatomy_Gray_1186

Anatomy_Gray.txt

Each pleural cavity is the potential space enclosed between the visceral and parietal pleurae. They normally contain only a very thin layer of serous fluid. As a result, the surface of the lung, which is covered by visceral pleura, directly opposes and freely slides over the parietal pleura attached to the wall.

Anatomy_Gray_1187

Anatomy_Gray.txt

The names given to the parietal pleura correspond to the parts of the wall with which they are associated (Fig. 3.38):

Anatomy_Gray_1188

Anatomy_Gray.txt

Pleura related to the ribs and intercostal spaces is termed the costal part.

Anatomy_Gray_1189

Anatomy_Gray.txt

Pleura covering the diaphragm is the diaphragmatic part.

Anatomy_Gray_1190

Anatomy_Gray.txt

Pleura covering the mediastinum is the mediastinal part.

Anatomy_Gray_1191

Anatomy_Gray.txt

The dome-shaped layer of parietal pleura lining the cervical extension of the pleural cavity is cervical pleura (dome of pleura or pleural cupola).

Anatomy_Gray_1192

Anatomy_Gray.txt

Covering the superior surface of the cervical pleura is a distinct dome-like layer of fascia, the suprapleural membrane (Fig. 3.38). This connective tissue membrane is attached laterally to the medial margin of the first rib and behind to the transverse process of vertebra CVII. Superiorly, the membrane receives muscle fibers from some of the deep muscles in the neck (scalene muscles) that function to keep the membrane taut. The suprapleural membrane provides apical support for the pleural cavity in the root of the neck.

Anatomy_Gray_1193

Anatomy_Gray.txt

In the region of vertebrae TV to TVII, the mediastinal pleura reflects off the mediastinum as a tubular, sleeve-like covering for structures (i.e., airway, vessels, nerves, lymphatics) that pass between the lung and mediastinum. This sleeve-like covering and the structures it contains forms the root of the lung. The root joins the medial surface of the lung at an area referred to as the hilum of the lung. Here, the mediastinal pleura is continuous with the visceral pleura.

Anatomy_Gray_1194

Anatomy_Gray.txt

The parietal pleural is innervated by somatic afferent fibers. The costal pleura is innervated by branches from the intercostal nerves, and pain would be felt in relation to the thoracic wall. The diaphragmatic pleura and the mediastinal pleura are innervated mainly by the phrenic nerves (originating at spinal cord levels C3, C4, and C5). Pain from these areas would refer to the C3, C4, and C5 dermatomes (lateral neck and the supraclavicular region of the shoulder).

Anatomy_Gray_1195

Anatomy_Gray.txt

The peripheral reflections of parietal pleura mark the extent of the pleural cavities (Fig. 3.39).

Anatomy_Gray_1196

Anatomy_Gray.txt

Superiorly, the pleural cavity can project as much as 3 to 4 cm above the first costal cartilage but does not extend above the neck of rib I. This limitation is caused by the inferior slope of rib I to its articulation with the manubrium.

Anatomy_Gray_1197

Anatomy_Gray.txt

Anteriorly, the pleural cavities approach each other posterior to the upper part of the sternum. However, posterior to the lower part of the sternum, the parietal pleura does not come as close to the midline on the left side as it does on the right because the middle mediastinum, containing the pericardium and heart, bulges to the left.

Anatomy_Gray_1198

Anatomy_Gray.txt

Inferiorly, the costal pleura reflects onto the diaphragm above the costal margin. In the midclavicular line, the pleural cavity extends inferiorly to approximately rib VIII. In the midaxillary line, it extends to rib X. From this point, the inferior margin courses somewhat horizontally, crossing ribs XI and XII to reach vertebra TXII. From the midclavicular line to the vertebral column, the inferior boundary of the pleura can be approximated by a line that runs between rib VIII, rib X, and vertebra TXII.

Anatomy_Gray_1199

Anatomy_Gray.txt

The visceral pleura is continuous with the parietal pleura at the hilum of each lung, where structures enter and leave the organ. The visceral pleura is firmly attached to the surface of the lung, including both opposed surfaces of the fissures that divide the lungs into lobes.