Learning ObjectivesBy the end of this section, you will be able to: Show Describe the components of the thoracic cage
The thoracic cage (rib cage) forms the thorax (chest) portion of the body. It consists of the 12 pairs of ribs with their costal cartilages and the sternum (Figure 7.5.1). The ribs are anchored posteriorly to the 12 thoracic vertebrae (T1–T12). The thoracic cage protects the heart and lungs. SternumThe sternum is the elongated bony structure that anchors the anterior thoracic cage. It consists of three parts: the manubrium, body, and xiphoid process. The manubrium is the wider, superior portion of the sternum. The top of the manubrium has a shallow, U-shaped border called the jugular (suprasternal) notch. This can be easily felt at the anterior base of the neck, between the medial ends of the clavicles. The clavicular notch is the shallow depression located on either side at the superior-lateral margins of the manubrium. This is the site of the sternoclavicular joint, between the sternum and clavicle. The first ribs also attach to the manubrium. The elongated, central portion of the sternum is the body. The manubrium and body join together at the sternal angle, so called because the junction between these two components is not flat, but forms a slight bend. The second rib attaches to the sternum at the sternal angle. Since the first rib is hidden behind the clavicle, the second rib is the highest rib that can be identified by palpation. Thus, the sternal angle and second rib are important landmarks for the identification and counting of the lower ribs. Ribs 3–7 attach to the sternal body. When assessing a patient’s level of alertness sometimes a sternal rub is performed with the knuckles to see if they respond to pain. The inferior tip of the sternum is the xiphoid process. This small structure is cartilaginous early in life, but gradually becomes ossified starting during middle age. RibsEach rib is a curved, flattened bone that contributes to the wall of the thorax. The ribs articulate posteriorly with the T1–T12 thoracic vertebrae, and most attach anteriorly via their costal cartilages to the sternum. There are 12 pairs of ribs. The ribs are numbered 1–12 in accordance with the thoracic vertebrae. Parts of a Typical RibThe posterior end of a typical rib is called the head of the rib (see Chapter 7.3 Figure 7.3.8). This region articulates primarily with the costal facet located on the body of the same numbered thoracic vertebra and to a lesser degree, with the costal facet located on the body of the next higher vertebra. Lateral to the head is the narrowed neck of the rib. A small bump on the posterior rib surface is the tubercle of the rib, which articulates with the facet located on the transverse process of the same numbered vertebra. The remainder of the rib is the body of the rib (shaft). Just lateral to the tubercle is the angle of the rib, the point at which the rib has its greatest degree of curvature. The angles of the ribs form the most posterior extent of the thoracic cage. In the anatomical position, the angles align with the medial border of the scapula. A shallow costal groove for the passage of blood vessels and a nerve is found along the inferior margin of each rib. Rib ClassificationsThe bony ribs do not extend anteriorly completely around to the sternum. Instead, each rib ends in a costal cartilage. These cartilages are made of hyaline cartilage and can extend for several inches. Most ribs are then attached, either directly or indirectly, to the sternum via their costal cartilage (see Figure 7.5.1). The ribs are classified into three groups based on their relationship to the sternum. Ribs 1–7 are classified as true ribs (vertebrosternal ribs). The costal cartilage from each of these ribs attaches directly to the sternum. Ribs 8–12 are called false ribs (vertebrochondral ribs). The costal cartilages from these ribs do not attach directly to the sternum. For ribs 8–10, the costal cartilages are attached to the cartilage of the next higher rib. Thus, the cartilage of rib 10 attaches to the cartilage of rib 9, rib 9 then attaches to rib 8, and rib 8 is attached to rib 7. The last two false ribs (11–12) are also called floating ribs (vertebral ribs). These are short ribs that do not attach to the sternum at all. Instead, their small costal cartilages terminate within the musculature of the lateral abdominal wall. Chapter ReviewThe thoracic cage protects the heart and lungs. It is composed of 12 pairs of ribs with their costal cartilages and the sternum. The ribs are anchored posteriorly to the 12 thoracic vertebrae. The sternum consists of the manubrium, body, and xiphoid process. The manubrium and body are joined at the sternal angle, which is also the site for attachment of the second ribs. Ribs are flattened, curved bones and are numbered 1–12. Posteriorly, the head of the rib articulates with the costal facets located on the bodies of thoracic vertebrae and the rib tubercle articulates with the facet located on the vertebral transverse process. The angle of the ribs forms the most posterior portion of the thoracic cage. The costal groove in the inferior margin of each rib carries blood vessels and a nerve. Anteriorly, each rib ends in a costal cartilage. True ribs (1–7) attach directly to the sternum via their costal cartilage. The false ribs (8–12) either attach to the sternum indirectly or not at all. Ribs 8–10 have their costal cartilages attached to the cartilage of the next higher rib. The floating ribs (11–12) are short and do not attach to the sternum or to another rib. Review QuestionsCritical Thinking Questions1. Define the parts and functions of the thoracic cage. 2. Describe the parts of the sternum. 3. Discuss the parts of a typical rib. 4. Define the classes of ribs. Glossaryangle of the ribportion of rib with greatest curvature; together, the rib angles form the most posterior extent of the thoracic cagebody of the ribshaft portion of a ribclavicular notchpaired notches located on the superior-lateral sides of the sternal manubrium, for articulation with the claviclecostal cartilagehyaline cartilage structure attached to the anterior end of each rib that provides for either direct or indirect attachment of most ribs to the sternumcostal grooveshallow groove along the inferior margin of a rib that provides passage for blood vessels and a nervefalse ribsvertebrochondral ribs 8–12 whose costal cartilage either attaches indirectly to the sternum via the costal cartilage of the next higher rib or does not attach to the sternum at allfloating ribsvertebral ribs 11–12 that do not attach to the sternum or to the costal cartilage of another ribhead of the ribposterior end of a rib that articulates with the bodies of thoracic vertebrae jugular (suprasternal) notchshallow notch located on superior surface of sternal manubriummanubriumexpanded, superior portion of the sternumneck of the ribnarrowed region of a rib, next to the rib headsternal anglejunction line between manubrium and body of the sternum and the site for attachment of the second rib to the sternumtrue ribsvertebrosternal ribs 1–7 that attach via their costal cartilage directly to the sternumtubercle of the ribsmall bump on the posterior side of a rib for articulation with the transverse process of a thoracic vertebraxiphoid processsmall process that forms the inferior tip of the sternumSolutionsAnswers for Critical Thinking Questions
Where is Xiphoid tip located?The xiphoid process is the smallest region of the sternum, or breastbone. It's made up of cartilage at birth but develops into bone in adulthood. It's located where the lower ribs attach to the breastbone. The tip of the xiphoid process resembles a sword.
What rib level is the xiphoid process?The thoracic outlet (inferior aperture) is bounded by the xiphoid process, costal arch, the rib 12.
What level is the sternum at?Anatomy. The sternal angle, which varies around 162 degrees in males, marks the approximate level of the 2nd pair of costal cartilages, which attach to the second ribs, and the level of the intervertebral disc between T4 and T5. In clinical applications, the sternal angle can be palpated at the T4 vertebral level.
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