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

id stringlengths 14 28	file_name stringclasses 18 values	content stringlengths 1 722k
Anatomy_Gray_1000	Anatomy_Gray.txt	In adults, the left brachiocephalic vein crosses the midline immediately posterior to the manubrium and delivers blood from the left side of the head and neck, the left upper limb, and part of the left thoracic wall into the superior vena cava.
Anatomy_Gray_1001	Anatomy_Gray.txt	The hemiazygos and accessory hemiazygos veins drain posterior and lateral parts of the left thoracic wall, pass immediately anterior to the bodies of thoracic vertebrae, and flow into the azygos vein on the right side, which ultimately connects with the superior vena cava.
Anatomy_Gray_1002	Anatomy_Gray.txt	The arrangement of vessels and nerves that supply the thoracic wall reflects the segmental organization of the wall. Arteries to the wall arise from two sources: the thoracic aorta, which is in the posterior mediastinum, and a pair of vessels, the internal thoracic arteries, which run along the deep aspect of the anterior thoracic wall on either side of the sternum.
Anatomy_Gray_1003	Anatomy_Gray.txt	the wall, mainly along the inferior margin of each rib (Fig. 3.12A). Running with these vessels are intercostal nerves (the anterior rami of thoracic spinal nerves), which innervate the wall, related parietal pleura, and associated skin. The position of these nerves and vessels relative to the ribs must be considered when passing objects, such as chest tubes, through the thoracic wall.
Anatomy_Gray_1004	Anatomy_Gray.txt	Dermatomes of the thorax generally reflect the segmental organization of the thoracic spinal nerves (Fig. 3.12B). The exception occurs, anteriorly and superiorly, with the first thoracic dermatome, which is located mostly in the upper limb, and not on the trunk.
Anatomy_Gray_1005	Anatomy_Gray.txt	The anterosuperior region of the trunk receives branches from the anterior ramus of C4 via supraclavicular branches of the cervical plexus.
Anatomy_Gray_1006	Anatomy_Gray.txt	The highest thoracic dermatome on the anterior chest wall is T2, which also extends into the upper limb.
Anatomy_Gray_1007	Anatomy_Gray.txt	In the midline, skin over the xiphoid process is innervated by T6.
Anatomy_Gray_1008	Anatomy_Gray.txt	Dermatomes of T7 to T12 follow the contour of the ribs onto the anterior abdominal wall (Fig. 3.12C).
Anatomy_Gray_1009	Anatomy_Gray.txt	All preganglionic nerve fibers of the sympathetic system are carried out of the spinal cord in spinal nerves T1 to L2 (Fig. 3.13). This means that sympathetic fibers found anywhere in the body ultimately emerge from the spinal cord as components of these spinal nerves. Preganglionic sympathetic fibers destined for the head are carried out of the spinal cord in spinal nerve T1.
Anatomy_Gray_1010	Anatomy_Gray.txt	The thoracic wall is expandable because most ribs articulate with other components of the wall by true joints that allow movement, and because of the shape and orientation of the ribs (Fig. 3.14).
Anatomy_Gray_1011	Anatomy_Gray.txt	A rib’s posterior attachment is superior to its anterior attachment. Therefore, when a rib is elevated, it moves the anterior thoracic wall forward relative to the posterior wall, which is fixed. In addition, the middle part of each rib is inferior to its two ends, so that when this region of the rib is elevated, it expands the thoracic wall laterally. Finally, because the diaphragm is muscular, it changes the volume of the thorax in the vertical direction.
Anatomy_Gray_1012	Anatomy_Gray.txt	Changes in the anterior, lateral, and vertical dimensions of the thoracic cavity are important for breathing.
Anatomy_Gray_1013	Anatomy_Gray.txt	Innervation of the diaphragm
Anatomy_Gray_1014	Anatomy_Gray.txt	The diaphragm is innervated by two phrenic nerves that originate, one on each side, as branches of the cervical plexus in the neck (Fig. 3.15). They arise from the anterior rami of cervical nerves C3, C4, and C5, with the major contribution coming from C4.
Anatomy_Gray_1015	Anatomy_Gray.txt	The phrenic nerves pass vertically through the neck, the superior thoracic aperture, and the mediastinum to supply motor innervation to the entire diaphragm, including the crura (muscular extensions that attach the diaphragm to the upper lumbar vertebrae). In the mediastinum, the phrenic nerves pass anteriorly to the roots of the lungs.
Anatomy_Gray_1016	Anatomy_Gray.txt	The tissues that initially give rise to the diaphragm are in an anterior position on the embryological disc before the head fold develops, which explains the cervical origin of the nerves that innervate the diaphragm. In other words, the tissue that gives rise to the diaphragm originates superior to the ultimate location of the diaphragm.
Anatomy_Gray_1017	Anatomy_Gray.txt	Spinal cord injuries below the level of the origin of the phrenic nerve do not affect movement of the diaphragm.
Anatomy_Gray_1018	Anatomy_Gray.txt	The cylindrical thorax consists of: a wall, two pleural cavities, the lungs, and the mediastinum.
Anatomy_Gray_1019	Anatomy_Gray.txt	The thorax houses the heart and lungs, acts as a conduit for structures passing between the neck and the abdomen, and plays a principal role in breathing. In addition, the thoracic wall protects the heart and lungs and provides support for the upper limbs. Muscles anchored to the anterior thoracic wall provide some of this support, and together with their associated connective tissues, nerves, and vessels, and the overlying skin and superficial fascia, define the pectoral region.
Anatomy_Gray_1020	Anatomy_Gray.txt	The pectoral region is external to the anterior thoracic wall and helps anchor the upper limb to the trunk. It consists of: a superficial compartment containing skin, superficial fascia, and breasts; and a deep compartment containing muscles and associated structures.
Anatomy_Gray_1021	Anatomy_Gray.txt	Nerves, vessels, and lymphatics in the superficial compartment emerge from the thoracic wall, the axilla, and the neck.
Anatomy_Gray_1022	Anatomy_Gray.txt	The breasts consist of mammary glands and associated skin and connective tissues. The mammary glands are modified sweat glands in the superficial fascia anterior to the pectoral muscles and the anterior thoracic wall (Fig. 3.16).
Anatomy_Gray_1023	Anatomy_Gray.txt	The mammary glands consist of a series of ducts and associated secretory lobules. These converge to form 15 to 20 lactiferous ducts, which open independently onto the nipple. The nipple is surrounded by a circular pigmented area of skin termed the areola.
Anatomy_Gray_1024	Anatomy_Gray.txt	A well-developed, connective tissue stroma surrounds the ducts and lobules of the mammary gland. In certain regions, this condenses to form well-defined ligaments, the suspensory ligaments of breast, which are continuous with the dermis of the skin and support the breast. Carcinoma of the breast creates tension on these ligaments, causing pitting of the skin.
Anatomy_Gray_1025	Anatomy_Gray.txt	In nonlactating women, the predominant component of the breasts is fat, while glandular tissue is more abundant in lactating women.
Anatomy_Gray_1026	Anatomy_Gray.txt	The breast lies on deep fascia related to the pectoralis major muscle and other surrounding muscles. A layer of loose connective tissue (the retromammary space) separates the breast from the deep fascia and provides some degree of movement over underlying structures.
Anatomy_Gray_1027	Anatomy_Gray.txt	The base, or attached surface, of each breast extends vertically from ribs II to VI, and transversely from the sternum to as far laterally as the midaxillary line.
Anatomy_Gray_1028	Anatomy_Gray.txt	The breast is related to the thoracic wall and to structures associated with the upper limb; therefore, vascular supply and drainage can occur by multiple routes (Fig. 3.16): laterally, vessels from the axillary artery—superior thoracic, thoraco-acromial, lateral thoracic, and subscapular arteries; medially, branches from the internal thoracic artery; the second to fourth intercostal arteries via branches that perforate the thoracic wall and overlying muscle.
Anatomy_Gray_1029	Anatomy_Gray.txt	Veins draining the breast parallel the arteries and ultimately drain into the axillary, internal thoracic, and intercostal veins.
Anatomy_Gray_1030	Anatomy_Gray.txt	Innervation of the breast is via anterior and lateral cutaneous branches of the second to sixth intercostal nerves. The nipple is innervated by the fourth intercostal nerve.
Anatomy_Gray_1031	Anatomy_Gray.txt	Lymphatic drainage of the breast is as follows:
Anatomy_Gray_1032	Anatomy_Gray.txt	Approximately 75% is via lymphatic vessels that drain laterally and superiorly into axillary nodes (Fig. 3.16).
Anatomy_Gray_1033	Anatomy_Gray.txt	Most of the remaining drainage is into parasternal nodes deep to the anterior thoracic wall and associated with the internal thoracic artery.
Anatomy_Gray_1034	Anatomy_Gray.txt	Some drainage may occur via lymphatic vessels that follow the lateral branches of posterior intercostal arteries and connect with intercostal nodes situated near the heads and necks of ribs.
Anatomy_Gray_1035	Anatomy_Gray.txt	Axillary nodes drain into the subclavian trunks, parasternal nodes drain into the bronchomediastinal trunks, and intercostal nodes drain either into the thoracic duct or into the bronchomediastinal trunks.
Anatomy_Gray_1036	Anatomy_Gray.txt	The breast in men is rudimentary and consists only of small ducts, often composed of cords of cells, that normally do not extend beyond the areola. Breast cancer can occur in men.
Anatomy_Gray_1037	Anatomy_Gray.txt	Muscles of the pectoral region
Anatomy_Gray_1038	Anatomy_Gray.txt	Each pectoral region contains the pectoralis major, pectoralis minor, and subclavius muscles (Fig. 3.17 and Table 3.1). All originate from the anterior thoracic wall and insert into bones of the upper limb.
Anatomy_Gray_1039	Anatomy_Gray.txt	The pectoralis major muscle is the largest and most superficial of the pectoral region muscles. It directly underlies the breast and is separated from it by deep fascia and the loose connective tissue of the retromammary space.
Anatomy_Gray_1040	Anatomy_Gray.txt	The pectoralis major has a broad origin that includes the anterior surfaces of the medial half of the clavicle, the sternum, and related costal cartilages. The muscle fibers converge to form a flat tendon, which inserts into the lateral lip of the intertubercular sulcus of the humerus.
Anatomy_Gray_1041	Anatomy_Gray.txt	The pectoralis major adducts, flexes, and medially rotates the arm.
Anatomy_Gray_1042	Anatomy_Gray.txt	The subclavius and pectoralis minor muscles underlie the pectoralis major:
Anatomy_Gray_1043	Anatomy_Gray.txt	The subclavius is small and passes laterally from the anterior and medial part of rib I to the inferior surface of the clavicle.
Anatomy_Gray_1044	Anatomy_Gray.txt	The pectoralis minor passes from the anterior surfaces of ribs III to V to the coracoid process of the scapula.
Anatomy_Gray_1045	Anatomy_Gray.txt	Both the subclavius and pectoralis minor pull the tip of the shoulder inferiorly.
Anatomy_Gray_1046	Anatomy_Gray.txt	A continuous layer of deep fascia, the clavipectoral fascia, encloses the subclavius and pectoralis minor and attaches to the clavicle above and to the floor of the axilla below.
Anatomy_Gray_1047	Anatomy_Gray.txt	The muscles of the pectoral region form the anterior wall of the axilla, a region between the upper limb and the neck through which all major structures pass. Nerves, vessels, and lymphatics that pass between the pectoral region and the axilla pass through the clavipectoral fascia between the subclavius and pectoralis minor or pass under the inferior margins of the pectoralis major and minor.
Anatomy_Gray_1048	Anatomy_Gray.txt	The thoracic wall is segmental in design and composed of skeletal elements and muscles. It extends between: the superior thoracic aperture, bordered by vertebra TI, rib I, and the manubrium of the sternum; and the inferior thoracic aperture, bordered by vertebra TXII, rib XII, the end of rib XI, the costal margin, and the xiphoid process of the sternum.
Anatomy_Gray_1049	Anatomy_Gray.txt	The skeletal elements of the thoracic wall consist of the thoracic vertebrae, intervertebral discs, ribs, and sternum.
Anatomy_Gray_1050	Anatomy_Gray.txt	There are twelve thoracic vertebrae, each of which is characterized by articulations with ribs.
Anatomy_Gray_1051	Anatomy_Gray.txt	A typical thoracic vertebra has a heart-shaped vertebral body, with roughly equal dimensions in the transverse and anteroposterior directions, and a long spinous process (Fig. 3.18). The vertebral foramen is generally circular and the laminae are broad and overlap with those of the vertebra below. The superior articular processes are flat, with their articular surfaces facing almost directly posteriorly, while the inferior articular processes project from the laminae and their articular facets face anteriorly. The transverse processes are club shaped and project posterolaterally.
Anatomy_Gray_1052	Anatomy_Gray.txt	Articulation with ribs
Anatomy_Gray_1053	Anatomy_Gray.txt	A typical thoracic vertebra has three sites on each side for articulation with ribs.
Anatomy_Gray_1054	Anatomy_Gray.txt	Two demifacets (i.e., partial facets) are located on the superior and inferior aspects of the body for articulation with corresponding sites on the heads of adjacent ribs. The superior costal facet articulates with part of the head of its own rib, and the inferior costal facet articulates with part of the head of the rib below.
Anatomy_Gray_1055	Anatomy_Gray.txt	An oval facet (transverse costal facet) at the end of the transverse process articulates with the tubercle of its own rib.
Anatomy_Gray_1056	Anatomy_Gray.txt	Not all vertebrae articulate with ribs in the same fashion (Fig. 3.19):
Anatomy_Gray_1057	Anatomy_Gray.txt	The superior costal facets on the body of vertebra TI are complete and articulate with a single facet on the head of its own rib—in other words, the head of rib I does not articulate with vertebra CVII.
Anatomy_Gray_1058	Anatomy_Gray.txt	Similarly, vertebra TX (and often TIX) articulates only with its own ribs and therefore lacks inferior demifacets on the body.
Anatomy_Gray_1059	Anatomy_Gray.txt	Vertebrae TXI and TXII articulate only with the heads of their own ribs—they lack transverse costal facets and have only a single complete facet on each side of their bodies.
Anatomy_Gray_1060	Anatomy_Gray.txt	There are twelve pairs of ribs, each terminating anteriorly in a costal cartilage (Fig. 3.20).
Anatomy_Gray_1061	Anatomy_Gray.txt	Although all ribs articulate with the vertebral column, only the costal cartilages of the upper seven ribs, known as true ribs, articulate directly with the sternum. The remaining five pairs of ribs are false ribs:
Anatomy_Gray_1062	Anatomy_Gray.txt	The costal cartilages of ribs VIII to X articulate anteriorly with the costal cartilages of the ribs above.
Anatomy_Gray_1063	Anatomy_Gray.txt	Ribs XI and XII have no anterior connection with other ribs or with the sternum and are often called floating ribs.
Anatomy_Gray_1064	Anatomy_Gray.txt	A typical rib consists of a curved shaft with anterior and posterior ends (Fig. 3.21). The anterior end is continuous with its costal cartilage. The posterior end articulates with the vertebral column and is characterized by a head, neck, and tubercle.
Anatomy_Gray_1065	Anatomy_Gray.txt	The head is somewhat expanded and typically presents two articular surfaces separated by a crest. The smaller superior surface articulates with the inferior costal facet on the body of the vertebra above, whereas the larger inferior facet articulates with the superior costal facet of its own vertebra.
Anatomy_Gray_1066	Anatomy_Gray.txt	The neck is a short flat region of bone that separates the head from the tubercle.
Anatomy_Gray_1067	Anatomy_Gray.txt	The tubercle projects posteriorly from the junction of the neck with the shaft and consists of two regions, an articular part and a nonarticular part:
Anatomy_Gray_1068	Anatomy_Gray.txt	The articular part is medial and has an oval facet for articulation with a corresponding facet on the transverse process of the associated vertebra.
Anatomy_Gray_1069	Anatomy_Gray.txt	The raised nonarticular part is roughened by ligament attachments.
Anatomy_Gray_1070	Anatomy_Gray.txt	The shaft is generally thin and flat with internal and external surfaces.
Anatomy_Gray_1071	Anatomy_Gray.txt	The superior margin is smooth and rounded, whereas the inferior margin is sharp. The shaft bends forward just laterally to the tubercle at a site termed the angle. It also has a gentle twist around its longitudinal axis so that the external surface of the anterior part of the shaft faces somewhat superiorly relative to the posterior part. The inferior margin of the internal surface is marked by a distinct costal groove.
Anatomy_Gray_1072	Anatomy_Gray.txt	Distinct features of upper and lower ribs
Anatomy_Gray_1073	Anatomy_Gray.txt	The upper and lower ribs have distinct features (Fig. 3.22).
Anatomy_Gray_1074	Anatomy_Gray.txt	Rib I is flat in the horizontal plane and has broad superior and inferior surfaces. From its articulation with vertebra TI, it slopes inferiorly to its attachment to the manubrium of the sternum. The head articulates only with the body of vertebra TI and therefore has only one articular surface. Like other ribs, the tubercle has a facet for articulation with the transverse process. The superior surface of the rib is characterized by a distinct tubercle, the scalene tubercle, which separates two smooth grooves that cross the rib approximately midway along the shaft. The anterior groove is caused by the subclavian vein, and the posterior groove is caused by the subclavian artery. Anterior and posterior to these grooves, the shaft is roughened by muscle and ligament attachments.
Anatomy_Gray_1075	Anatomy_Gray.txt	Rib II, like rib I, is flat but twice as long. It articulates with the vertebral column in a way typical of most ribs.
Anatomy_Gray_1076	Anatomy_Gray.txt	The head of rib X has a single facet for articulation with its own vertebra.
Anatomy_Gray_1077	Anatomy_Gray.txt	Ribs XI and XII articulate only with the bodies of their own vertebrae and have no tubercles or necks. Both ribs are short, have little curve, and are pointed anteriorly.
Anatomy_Gray_1078	Anatomy_Gray.txt	The adult sternum consists of three major elements: the broad and superiorly positioned manubrium of the sternum, the narrow and longitudinally oriented body of the sternum, and the small and inferiorly positioned xiphoid process (Fig. 3.23).
Anatomy_Gray_1079	Anatomy_Gray.txt	Manubrium of the sternum
Anatomy_Gray_1080	Anatomy_Gray.txt	The manubrium of the sternum forms part of the bony framework of the neck and the thorax.
Anatomy_Gray_1081	Anatomy_Gray.txt	The superior surface of the manubrium is expanded laterally and bears a distinct and palpable notch, the jugular notch (suprasternal notch), in the midline.
Anatomy_Gray_1082	Anatomy_Gray.txt	On either side of this notch is a large oval fossa for articulation with the clavicle. Immediately inferior to this fossa, on each lateral surface of the manubrium, is a facet for the attachment of the first costal cartilage. At the lower end of the lateral border is a demifacet for articulation with the upper half of the anterior end of the second costal cartilage.
Anatomy_Gray_1083	Anatomy_Gray.txt	Body of the sternum
Anatomy_Gray_1084	Anatomy_Gray.txt	The body of the sternum is flat.
Anatomy_Gray_1085	Anatomy_Gray.txt	The anterior surface of the body of the sternum is often marked by transverse ridges that represent lines of fusion between the segmental elements called sternebrae, from which this part of the sternum arises embryologically.
Anatomy_Gray_1086	Anatomy_Gray.txt	The lateral margins of the body of the sternum have articular facets for costal cartilages. Superiorly, each lateral margin has a demifacet for articulation with the inferior aspect of the second costal cartilage. Inferior to this demifacet are four facets for articulation with the costal cartilages of ribs III to VI.
Anatomy_Gray_1087	Anatomy_Gray.txt	At the inferior end of the body of the sternum is a demifacet for articulation with the upper demifacet on the seventh costal cartilage. The inferior end of the body of the sternum is attached to the xiphoid process.
Anatomy_Gray_1088	Anatomy_Gray.txt	The xiphoid process is the smallest part of the sternum. Its shape is variable: it may be wide, thin, pointed, bifid, curved, or perforated. It begins as a cartilaginous structure, which becomes ossified in the adult. On each side of its upper lateral margin is a demifacet for articulation with the inferior end of the seventh costal cartilage.
Anatomy_Gray_1089	Anatomy_Gray.txt	A typical rib articulates with: the bodies of adjacent vertebrae, forming a joint with the head of the rib; and the transverse process of its related vertebra, forming a costotransverse joint (Fig. 3.24).
Anatomy_Gray_1090	Anatomy_Gray.txt	Together, the costovertebral joints and related ligaments allow the necks of the ribs either to rotate around their longitudinal axes, which occurs mainly in the upper ribs, or to ascend and descend relative to the vertebral column, which occurs mainly in the lower ribs. The combined movements of all of the ribs on the vertebral column are essential for altering the volume of the thoracic cavity during breathing.
Anatomy_Gray_1091	Anatomy_Gray.txt	Joint with head of rib
Anatomy_Gray_1092	Anatomy_Gray.txt	The two facets on the head of the rib articulate with the superior facet on the body of its own vertebra and with the inferior facet on the body of the vertebra above. This joint is divided into two synovial compartments by an intra-articular ligament, which attaches the crest to the adjacent intervertebral disc and separates the two articular surfaces on the head of the rib. The two synovial compartments and the intervening ligament are surrounded by a single joint capsule attached to the outer margins of the combined articular surfaces of the head and vertebral column.
Anatomy_Gray_1093	Anatomy_Gray.txt	Costotransverse joints are synovial joints between the tubercle of a rib and the transverse process of the related vertebra (Fig. 3.24). The capsule surrounding each joint is thin. The joint is stabilized by two strong extracapsular ligaments that span the space between the transverse process and the rib on the medial and lateral sides of the joint:
Anatomy_Gray_1094	Anatomy_Gray.txt	The costotransverse ligament is medial to the joint and attaches the neck of the rib to the transverse process.
Anatomy_Gray_1095	Anatomy_Gray.txt	The lateral costotransverse ligament is lateral to the joint and attaches the tip of the transverse process to the roughened nonarticular part of the tubercle of the rib.
Anatomy_Gray_1096	Anatomy_Gray.txt	A third ligament, the superior costotransverse ligament, attaches the superior surface of the neck of the rib to the transverse process of the vertebra above.
Anatomy_Gray_1097	Anatomy_Gray.txt	Slight gliding movements occur at the costotransverse joints.
Anatomy_Gray_1098	Anatomy_Gray.txt	The sternocostal joints are joints between the upper seven costal cartilages and the sternum (Fig. 3.25).
Anatomy_Gray_1099	Anatomy_Gray.txt	The joint between rib I and the manubrium is not synovial and consists of a fibrocartilaginous connection between the manubrium and the costal cartilage. The second to seventh joints are synovial and have thin capsules reinforced by surrounding sternocostal ligaments.

Anatomy_Gray_1000

Anatomy_Gray.txt

In adults, the left brachiocephalic vein crosses the midline immediately posterior to the manubrium and delivers blood from the left side of the head and neck, the left upper limb, and part of the left thoracic wall into the superior vena cava.

Anatomy_Gray_1001

Anatomy_Gray.txt

The hemiazygos and accessory hemiazygos veins drain posterior and lateral parts of the left thoracic wall, pass immediately anterior to the bodies of thoracic vertebrae, and flow into the azygos vein on the right side, which ultimately connects with the superior vena cava.

Anatomy_Gray_1002

Anatomy_Gray.txt

The arrangement of vessels and nerves that supply the thoracic wall reflects the segmental organization of the wall. Arteries to the wall arise from two sources: the thoracic aorta, which is in the posterior mediastinum, and a pair of vessels, the internal thoracic arteries, which run along the deep aspect of the anterior thoracic wall on either side of the sternum.

Anatomy_Gray_1003

Anatomy_Gray.txt

the wall, mainly along the inferior margin of each rib (Fig. 3.12A). Running with these vessels are intercostal nerves (the anterior rami of thoracic spinal nerves), which innervate the wall, related parietal pleura, and associated skin. The position of these nerves and vessels relative to the ribs must be considered when passing objects, such as chest tubes, through the thoracic wall.

Anatomy_Gray_1004

Anatomy_Gray.txt

Dermatomes of the thorax generally reflect the segmental organization of the thoracic spinal nerves (Fig. 3.12B). The exception occurs, anteriorly and superiorly, with the first thoracic dermatome, which is located mostly in the upper limb, and not on the trunk.

Anatomy_Gray_1005

Anatomy_Gray.txt

The anterosuperior region of the trunk receives branches from the anterior ramus of C4 via supraclavicular branches of the cervical plexus.

Anatomy_Gray_1006

Anatomy_Gray.txt

The highest thoracic dermatome on the anterior chest wall is T2, which also extends into the upper limb.

Anatomy_Gray_1007

Anatomy_Gray.txt

In the midline, skin over the xiphoid process is innervated by T6.

Anatomy_Gray_1008

Anatomy_Gray.txt

Dermatomes of T7 to T12 follow the contour of the ribs onto the anterior abdominal wall (Fig. 3.12C).

Anatomy_Gray_1009

Anatomy_Gray.txt

All preganglionic nerve fibers of the sympathetic system are carried out of the spinal cord in spinal nerves T1 to L2 (Fig. 3.13). This means that sympathetic fibers found anywhere in the body ultimately emerge from the spinal cord as components of these spinal nerves. Preganglionic sympathetic fibers destined for the head are carried out of the spinal cord in spinal nerve T1.

Anatomy_Gray_1010

Anatomy_Gray.txt

The thoracic wall is expandable because most ribs articulate with other components of the wall by true joints that allow movement, and because of the shape and orientation of the ribs (Fig. 3.14).

Anatomy_Gray_1011

Anatomy_Gray.txt

A rib’s posterior attachment is superior to its anterior attachment. Therefore, when a rib is elevated, it moves the anterior thoracic wall forward relative to the posterior wall, which is fixed. In addition, the middle part of each rib is inferior to its two ends, so that when this region of the rib is elevated, it expands the thoracic wall laterally. Finally, because the diaphragm is muscular, it changes the volume of the thorax in the vertical direction.

Anatomy_Gray_1012

Anatomy_Gray.txt

Changes in the anterior, lateral, and vertical dimensions of the thoracic cavity are important for breathing.

Anatomy_Gray_1013

Anatomy_Gray.txt

Innervation of the diaphragm

Anatomy_Gray_1014

Anatomy_Gray.txt

The diaphragm is innervated by two phrenic nerves that originate, one on each side, as branches of the cervical plexus in the neck (Fig. 3.15). They arise from the anterior rami of cervical nerves C3, C4, and C5, with the major contribution coming from C4.

Anatomy_Gray_1015

Anatomy_Gray.txt

The phrenic nerves pass vertically through the neck, the superior thoracic aperture, and the mediastinum to supply motor innervation to the entire diaphragm, including the crura (muscular extensions that attach the diaphragm to the upper lumbar vertebrae). In the mediastinum, the phrenic nerves pass anteriorly to the roots of the lungs.

Anatomy_Gray_1016

Anatomy_Gray.txt

The tissues that initially give rise to the diaphragm are in an anterior position on the embryological disc before the head fold develops, which explains the cervical origin of the nerves that innervate the diaphragm. In other words, the tissue that gives rise to the diaphragm originates superior to the ultimate location of the diaphragm.

Anatomy_Gray_1017

Anatomy_Gray.txt

Spinal cord injuries below the level of the origin of the phrenic nerve do not affect movement of the diaphragm.

Anatomy_Gray_1018

Anatomy_Gray.txt

The cylindrical thorax consists of: a wall, two pleural cavities, the lungs, and the mediastinum.

Anatomy_Gray_1019

Anatomy_Gray.txt

The thorax houses the heart and lungs, acts as a conduit for structures passing between the neck and the abdomen, and plays a principal role in breathing. In addition, the thoracic wall protects the heart and lungs and provides support for the upper limbs. Muscles anchored to the anterior thoracic wall provide some of this support, and together with their associated connective tissues, nerves, and vessels, and the overlying skin and superficial fascia, define the pectoral region.

Anatomy_Gray_1020

Anatomy_Gray.txt

The pectoral region is external to the anterior thoracic wall and helps anchor the upper limb to the trunk. It consists of: a superficial compartment containing skin, superficial fascia, and breasts; and a deep compartment containing muscles and associated structures.

Anatomy_Gray_1021

Anatomy_Gray.txt

Nerves, vessels, and lymphatics in the superficial compartment emerge from the thoracic wall, the axilla, and the neck.

Anatomy_Gray_1022

Anatomy_Gray.txt

The breasts consist of mammary glands and associated skin and connective tissues. The mammary glands are modified sweat glands in the superficial fascia anterior to the pectoral muscles and the anterior thoracic wall (Fig. 3.16).

Anatomy_Gray_1023

Anatomy_Gray.txt

The mammary glands consist of a series of ducts and associated secretory lobules. These converge to form 15 to 20 lactiferous ducts, which open independently onto the nipple. The nipple is surrounded by a circular pigmented area of skin termed the areola.

Anatomy_Gray_1024

Anatomy_Gray.txt

A well-developed, connective tissue stroma surrounds the ducts and lobules of the mammary gland. In certain regions, this condenses to form well-defined ligaments, the suspensory ligaments of breast, which are continuous with the dermis of the skin and support the breast. Carcinoma of the breast creates tension on these ligaments, causing pitting of the skin.

Anatomy_Gray_1025

Anatomy_Gray.txt

In nonlactating women, the predominant component of the breasts is fat, while glandular tissue is more abundant in lactating women.

Anatomy_Gray_1026

Anatomy_Gray.txt

The breast lies on deep fascia related to the pectoralis major muscle and other surrounding muscles. A layer of loose connective tissue (the retromammary space) separates the breast from the deep fascia and provides some degree of movement over underlying structures.

Anatomy_Gray_1027

Anatomy_Gray.txt

The base, or attached surface, of each breast extends vertically from ribs II to VI, and transversely from the sternum to as far laterally as the midaxillary line.

Anatomy_Gray_1028

Anatomy_Gray.txt

The breast is related to the thoracic wall and to structures associated with the upper limb; therefore, vascular supply and drainage can occur by multiple routes (Fig. 3.16): laterally, vessels from the axillary artery—superior thoracic, thoraco-acromial, lateral thoracic, and subscapular arteries; medially, branches from the internal thoracic artery; the second to fourth intercostal arteries via branches that perforate the thoracic wall and overlying muscle.

Anatomy_Gray_1029

Anatomy_Gray.txt

Veins draining the breast parallel the arteries and ultimately drain into the axillary, internal thoracic, and intercostal veins.

Anatomy_Gray_1030

Anatomy_Gray.txt

Innervation of the breast is via anterior and lateral cutaneous branches of the second to sixth intercostal nerves. The nipple is innervated by the fourth intercostal nerve.

Anatomy_Gray_1031

Anatomy_Gray.txt

Lymphatic drainage of the breast is as follows:

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Approximately 75% is via lymphatic vessels that drain laterally and superiorly into axillary nodes (Fig. 3.16).

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Most of the remaining drainage is into parasternal nodes deep to the anterior thoracic wall and associated with the internal thoracic artery.

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Some drainage may occur via lymphatic vessels that follow the lateral branches of posterior intercostal arteries and connect with intercostal nodes situated near the heads and necks of ribs.

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Axillary nodes drain into the subclavian trunks, parasternal nodes drain into the bronchomediastinal trunks, and intercostal nodes drain either into the thoracic duct or into the bronchomediastinal trunks.

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The breast in men is rudimentary and consists only of small ducts, often composed of cords of cells, that normally do not extend beyond the areola. Breast cancer can occur in men.

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Muscles of the pectoral region

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Each pectoral region contains the pectoralis major, pectoralis minor, and subclavius muscles (Fig. 3.17 and Table 3.1). All originate from the anterior thoracic wall and insert into bones of the upper limb.

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The pectoralis major muscle is the largest and most superficial of the pectoral region muscles. It directly underlies the breast and is separated from it by deep fascia and the loose connective tissue of the retromammary space.

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The pectoralis major has a broad origin that includes the anterior surfaces of the medial half of the clavicle, the sternum, and related costal cartilages. The muscle fibers converge to form a flat tendon, which inserts into the lateral lip of the intertubercular sulcus of the humerus.

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The pectoralis major adducts, flexes, and medially rotates the arm.

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The subclavius and pectoralis minor muscles underlie the pectoralis major:

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The subclavius is small and passes laterally from the anterior and medial part of rib I to the inferior surface of the clavicle.

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The pectoralis minor passes from the anterior surfaces of ribs III to V to the coracoid process of the scapula.

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Both the subclavius and pectoralis minor pull the tip of the shoulder inferiorly.

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A continuous layer of deep fascia, the clavipectoral fascia, encloses the subclavius and pectoralis minor and attaches to the clavicle above and to the floor of the axilla below.

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The muscles of the pectoral region form the anterior wall of the axilla, a region between the upper limb and the neck through which all major structures pass. Nerves, vessels, and lymphatics that pass between the pectoral region and the axilla pass through the clavipectoral fascia between the subclavius and pectoralis minor or pass under the inferior margins of the pectoralis major and minor.

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The thoracic wall is segmental in design and composed of skeletal elements and muscles. It extends between: the superior thoracic aperture, bordered by vertebra TI, rib I, and the manubrium of the sternum; and the inferior thoracic aperture, bordered by vertebra TXII, rib XII, the end of rib XI, the costal margin, and the xiphoid process of the sternum.

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The skeletal elements of the thoracic wall consist of the thoracic vertebrae, intervertebral discs, ribs, and sternum.

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There are twelve thoracic vertebrae, each of which is characterized by articulations with ribs.

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A typical thoracic vertebra has a heart-shaped vertebral body, with roughly equal dimensions in the transverse and anteroposterior directions, and a long spinous process (Fig. 3.18). The vertebral foramen is generally circular and the laminae are broad and overlap with those of the vertebra below. The superior articular processes are flat, with their articular surfaces facing almost directly posteriorly, while the inferior articular processes project from the laminae and their articular facets face anteriorly. The transverse processes are club shaped and project posterolaterally.

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Articulation with ribs

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A typical thoracic vertebra has three sites on each side for articulation with ribs.

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Two demifacets (i.e., partial facets) are located on the superior and inferior aspects of the body for articulation with corresponding sites on the heads of adjacent ribs. The superior costal facet articulates with part of the head of its own rib, and the inferior costal facet articulates with part of the head of the rib below.

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An oval facet (transverse costal facet) at the end of the transverse process articulates with the tubercle of its own rib.

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Not all vertebrae articulate with ribs in the same fashion (Fig. 3.19):

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The superior costal facets on the body of vertebra TI are complete and articulate with a single facet on the head of its own rib—in other words, the head of rib I does not articulate with vertebra CVII.

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Similarly, vertebra TX (and often TIX) articulates only with its own ribs and therefore lacks inferior demifacets on the body.

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Vertebrae TXI and TXII articulate only with the heads of their own ribs—they lack transverse costal facets and have only a single complete facet on each side of their bodies.

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There are twelve pairs of ribs, each terminating anteriorly in a costal cartilage (Fig. 3.20).

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Although all ribs articulate with the vertebral column, only the costal cartilages of the upper seven ribs, known as true ribs, articulate directly with the sternum. The remaining five pairs of ribs are false ribs:

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The costal cartilages of ribs VIII to X articulate anteriorly with the costal cartilages of the ribs above.

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Ribs XI and XII have no anterior connection with other ribs or with the sternum and are often called floating ribs.

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A typical rib consists of a curved shaft with anterior and posterior ends (Fig. 3.21). The anterior end is continuous with its costal cartilage. The posterior end articulates with the vertebral column and is characterized by a head, neck, and tubercle.

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The head is somewhat expanded and typically presents two articular surfaces separated by a crest. The smaller superior surface articulates with the inferior costal facet on the body of the vertebra above, whereas the larger inferior facet articulates with the superior costal facet of its own vertebra.

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The neck is a short flat region of bone that separates the head from the tubercle.

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The tubercle projects posteriorly from the junction of the neck with the shaft and consists of two regions, an articular part and a nonarticular part:

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The articular part is medial and has an oval facet for articulation with a corresponding facet on the transverse process of the associated vertebra.

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The raised nonarticular part is roughened by ligament attachments.

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The shaft is generally thin and flat with internal and external surfaces.

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The superior margin is smooth and rounded, whereas the inferior margin is sharp. The shaft bends forward just laterally to the tubercle at a site termed the angle. It also has a gentle twist around its longitudinal axis so that the external surface of the anterior part of the shaft faces somewhat superiorly relative to the posterior part. The inferior margin of the internal surface is marked by a distinct costal groove.

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Distinct features of upper and lower ribs

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The upper and lower ribs have distinct features (Fig. 3.22).

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Rib I is flat in the horizontal plane and has broad superior and inferior surfaces. From its articulation with vertebra TI, it slopes inferiorly to its attachment to the manubrium of the sternum. The head articulates only with the body of vertebra TI and therefore has only one articular surface. Like other ribs, the tubercle has a facet for articulation with the transverse process. The superior surface of the rib is characterized by a distinct tubercle, the scalene tubercle, which separates two smooth grooves that cross the rib approximately midway along the shaft. The anterior groove is caused by the subclavian vein, and the posterior groove is caused by the subclavian artery. Anterior and posterior to these grooves, the shaft is roughened by muscle and ligament attachments.

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Rib II, like rib I, is flat but twice as long. It articulates with the vertebral column in a way typical of most ribs.

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The head of rib X has a single facet for articulation with its own vertebra.

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Ribs XI and XII articulate only with the bodies of their own vertebrae and have no tubercles or necks. Both ribs are short, have little curve, and are pointed anteriorly.

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The adult sternum consists of three major elements: the broad and superiorly positioned manubrium of the sternum, the narrow and longitudinally oriented body of the sternum, and the small and inferiorly positioned xiphoid process (Fig. 3.23).

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Manubrium of the sternum

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The manubrium of the sternum forms part of the bony framework of the neck and the thorax.

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The superior surface of the manubrium is expanded laterally and bears a distinct and palpable notch, the jugular notch (suprasternal notch), in the midline.

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On either side of this notch is a large oval fossa for articulation with the clavicle. Immediately inferior to this fossa, on each lateral surface of the manubrium, is a facet for the attachment of the first costal cartilage. At the lower end of the lateral border is a demifacet for articulation with the upper half of the anterior end of the second costal cartilage.

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Body of the sternum

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The body of the sternum is flat.

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The anterior surface of the body of the sternum is often marked by transverse ridges that represent lines of fusion between the segmental elements called sternebrae, from which this part of the sternum arises embryologically.

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The lateral margins of the body of the sternum have articular facets for costal cartilages. Superiorly, each lateral margin has a demifacet for articulation with the inferior aspect of the second costal cartilage. Inferior to this demifacet are four facets for articulation with the costal cartilages of ribs III to VI.

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At the inferior end of the body of the sternum is a demifacet for articulation with the upper demifacet on the seventh costal cartilage. The inferior end of the body of the sternum is attached to the xiphoid process.

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The xiphoid process is the smallest part of the sternum. Its shape is variable: it may be wide, thin, pointed, bifid, curved, or perforated. It begins as a cartilaginous structure, which becomes ossified in the adult. On each side of its upper lateral margin is a demifacet for articulation with the inferior end of the seventh costal cartilage.

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A typical rib articulates with: the bodies of adjacent vertebrae, forming a joint with the head of the rib; and the transverse process of its related vertebra, forming a costotransverse joint (Fig. 3.24).

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Together, the costovertebral joints and related ligaments allow the necks of the ribs either to rotate around their longitudinal axes, which occurs mainly in the upper ribs, or to ascend and descend relative to the vertebral column, which occurs mainly in the lower ribs. The combined movements of all of the ribs on the vertebral column are essential for altering the volume of the thoracic cavity during breathing.

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Joint with head of rib

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The two facets on the head of the rib articulate with the superior facet on the body of its own vertebra and with the inferior facet on the body of the vertebra above. This joint is divided into two synovial compartments by an intra-articular ligament, which attaches the crest to the adjacent intervertebral disc and separates the two articular surfaces on the head of the rib. The two synovial compartments and the intervening ligament are surrounded by a single joint capsule attached to the outer margins of the combined articular surfaces of the head and vertebral column.

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Costotransverse joints are synovial joints between the tubercle of a rib and the transverse process of the related vertebra (Fig. 3.24). The capsule surrounding each joint is thin. The joint is stabilized by two strong extracapsular ligaments that span the space between the transverse process and the rib on the medial and lateral sides of the joint:

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The costotransverse ligament is medial to the joint and attaches the neck of the rib to the transverse process.

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The lateral costotransverse ligament is lateral to the joint and attaches the tip of the transverse process to the roughened nonarticular part of the tubercle of the rib.

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A third ligament, the superior costotransverse ligament, attaches the superior surface of the neck of the rib to the transverse process of the vertebra above.

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Slight gliding movements occur at the costotransverse joints.

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The sternocostal joints are joints between the upper seven costal cartilages and the sternum (Fig. 3.25).

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The joint between rib I and the manubrium is not synovial and consists of a fibrocartilaginous connection between the manubrium and the costal cartilage. The second to seventh joints are synovial and have thin capsules reinforced by surrounding sternocostal ligaments.