140 Introduction to Anatomy & Physiology • The remainder of the bony portion of the sternum is the body of the sternum. • At the lower end of the sternum is a projection called the xiphoid (ZIGH-foyd) process. There are 12 pairs of ribs in the thoracic cage, as shown in Figure 4.16. • The first seven pairs (1–7) attach directly to the sternum and are, therefore, called true ribs. • The next three pairs of ribs (8–10) are called false ribs because they have cartilaginous (kar-ti-LAJ-i-nuhs) attachments to the cartilage of the seventh rib, rather than attaching directly to the sternum. • The lowest two pairs of ribs (11–12) are known as floating ribs, because they do not attach to bone or cartilage in front of the body. Check Your Understanding 1. Which bones make up the thoracic cage? 2. List the three regions of the sternum. 3. How many pairs of ribs are in the thoracic cage? The Hyoid Bone Technically not part of the cranium, spine, or thoracic cage, the hyoid bone is considered part of the axial skeleton. It is located at the base of the mandible and helps with movements of the tongue, larynx, and pharynx. The Thoracic Cage The ribs, sternum, and thoracic vertebrae are collectively known as the thoracic cage, or bony thorax. Why are these bones given this name? It is because together they form a protective, bony “cage” that surrounds the heart and lungs in the thoracic cavity, as shown in Figure 4.16. The sternum (STER-num), or breastbone, includes three regions: • The manubrium (ma-NOO-bree-um) is the upper portion of the sternum. It has articulations to the left and right bones of the clavicle, or collarbone, as well as to the first and second ribs. © Body Scientific International Figure 4.16 The thoracic cage. Why are the false ribs called false ribs? Costal cartilage Floating ribs False ribs True ribs 1 2 3 4 5 6 7 8 9 10 11 12 Manubrium Xiphoid process Body Sternum Clavicle Copyright Goodheart-Willcox Co., Inc.