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Both the radius and the ulna exhibit interosseous borders, which face each other; the ulna's interosseous border projects laterally, whereas the radius's interosseous border projects medially. These interosseous borders are connected by an interosseous membrane (interosseous ligament), composed of dense regular connective tissue. This membrane helps keep the radius and ulna a fixed distance apart from one another and provides a pivot of rotation for the forearm. The bony joints that move during this rotation are the proximal and distal radioulnar joints (figure 8.5b, c). In anatomic position, the palm of the hand is facing anteriorly, and the bones of the forearm are said to be in supination (sū′pi-nā′shŭn) (figure 8.5d). The radius and the ulna are parallel with one another. If you stand in anatomic position, so that you can view your own forearm, the radius is on the lateral (thumb) side of the forearm, whereas the ulna is on the medial (little finger) side of the forearm.
A Colles (kol′ēz) fracture is a fracture of the distal radius (see figure 6.15). This type of fracture typically occurs when a person extends a hand (and thus the forearm is pronated) while trying to break a fall. The force of the fall on the outstretched hand fractures the distal radius, which is displaced posteriorly. The force can be transmitted via the interosseous membrane to the ulna and may also result in a distal ulna fracture. Colles fractures are very common in adults, especially in elderly individuals who suffer from osteoporosis. The common symptoms of a Colles fracture are pain and swelling just proximal to the wrist and weakness in the affected hand. In addition, when viewed from the side, the wrist is not straight, but is bent at an angle similar to the shape of a dinner fork, because of the displacement of the broken segment.
The patella (pa-tel′ă; patina = shallow disk), or kneecap, is a large, roughly triangular sesamoid bone located within the tendon of the quadriceps femoris muscle (figure 8.12). The patella allows the tendon of the quadriceps femoris to glide more smoothly by distributing the force placed on the tendon, and it protects the knee joint. The superior base of the patella is broad, and its inferior apex is pointed. The patella may be easily palpated along the anterior surface of the knee. The posterior aspect of the patella has an articular surface that articulates (connects) with the patellar surface of the femur.
Anatomists identify the part of the lower limb between the knee and the ankle as the crural region, or leg. The skeleton of the leg has two parallel bones, the thick, strong tibia and a slender fibula (figure 8.13). These two bones are connected by an interosseous membrane composed of dense regular connective tissue, which extends between their interosseous borders. The interosseous membrane stabilizes the relative positions of the tibia and fibula, and additionally provides a pivot of minimal rotation for the two bones.
The clavicle can fracture relatively easily because its S shape does not allow it to resist stress. In addition, the sternoclavicular joint is incredibly strong, so if stress is placed on both the clavicle and the joint, the clavicle will fracture before the joint is damaged. A direct blow to the middle part of the clavicle, a fall onto the lateral border of the shoulder, or use of the arms to brace against a forward fall is often stress enough to fracture the clavicle. Because the clavicle has an anterior and posterior curve along its length between the medial and lateral edges, severe stress to the mid-region of the bone usually results in an anterior fracture. A posterior fracture may be more serious because bone splinters can penetrate the subclavian artery and vein, which lie immediately posterior and inferior to the clavicle and are the primary blood vessels supplying the upper limb.
Between these borders are the superior, inferior, and lateral angles. The superior angle is the pointed part of the scapula between the superior and medial borders, whereas the inferior angle is located between the medial and lateral borders. The lateral angle is composed primarily of the cup-shaped, shallow glenoid (glē′noyd; Page 224resembling a socket) cavity, or glenoid fossa, which articulates with the humerus, the bone of the arm. Tubercles (tū′bĕr-kĕl) on the superior and inferior edges of the glenoid cavity serve as attachment sites for the muscles that position the shoulder and arm. Near the superior edge of the glenoid cavity is the supraglenoid tubercle, and near the inferior edge is the infraglenoid tubercle.
The metatarsal (met′ă-tar′săl) bones of the foot are five long bones similar in arrangement and name to the metacarpal bones of the hand. They form the sole of the foot and are identified with Roman numerals I-V, proceeding medially to laterally across the sole (figure 8.14). Metatarsals I through III articulate with the three cuneiform bones, and metatarsals IV and V articulate with the cuboid bone. Distally, each metatarsal bone articulates with a proximal phalanx. At the head of the first metatarsal are two tiny sesamoid bones, which insert on the tendons of the flexor hallucis brevis muscle and help these tendons move more freely by distributing the force more evenly along them. The bones of the toes (like the bones of the fingers) are called phalanges. The toes contain 14 phalanges. The great toe is the hallux (hal′ŭks; hallex = great toe), and it has only two phalanges (proximal and distal); each of the other four toes has three phalanges (proximal, middle, and distal).
Normally, the sole of the foot is arched, which helps it support the weight of the body and ensures that the blood vessels and nerves on the sole of the foot are not pinched when we are standing. The three arches of the foot are the medial longitudinal, lateral longitudinal, and transverse arches
Although it is possible to determine the sex of a skeleton by examining the skull (see section 7.2), the most reliable indicator of sex is the pelvis, primarily the ossa coxae. The ossa coxae are the most sexually dimorphic bones of the body due to the requirements of pregnancy and childbirth in females. For example, the female pelvis is shallower and wider than the male pelvis to accommodate an infant's head as it passes through the birth canal. Some of these differences are obvious, such as that males have narrower hips than females do. But we can find many other differences by examining the shapes and orientations of the pelvic bones. For example, the female ilium flares more laterally, and the male ilium projects more superiorly, which is why males typically have narrower hips. Because the female pelvis is wider, the greater sciatic notch is much wider as well. In contrast, the male greater sciatic notch is much narrower and U-shaped. Females tend to have a preauricular sulcus, which is a depression/groove between the greater sciatic notch and the sacroiliac articulation. Males tend not to have this sulcus. The sacrum is usually shorter and wider in females. The coccyx projects more vertically in males, whereas the female coccyx has a posterior tilt.
The body of the pubis in females is much longer and almost rectangular in shape, compared to the shorter, triangular male pubic body. The subpubic angle (or pubic arch) is the angle formed when the left and right pubic bones are aligned at their pubic symphyses. Because females have much longer pubic bones, the corresponding subpubic angle is much wider and more convex, usually much greater Page 236than 100 degrees. The male pubic arch is much narrower and typically does not extend past 90 degrees.
The scaphoid bone is one of the more commonly fractured carpal bones. A fall on the outstretched hand may cause the scaphoid to fracture into two separate pieces. When this happens, only one of the two pieces maintains its blood supply. Usually, blood vessels are torn on the proximal part of the scaphoid, resulting in avascular necrosis, death of the bone tissue in that area due to inadequate blood supply. Scaphoid fractures take a very long time to heal properly due to this complication. Additionally, avascular necrosis may cause the patient to develop degenerative joint disease of the wrist.
The bones in the palm of the hand are called metacarpals (met′ă-kar′păl; meta = after, karpus = wrist). Five metacarpal bones articulate with the distal carpal bones and support the palm. Roman numerals I-V denote the metacarpal bones, with metacarpal I located at the base of the thumb, and metacarpal V at the base of the little finger. The bones of the digits are the phalanges (fă-lan′jēz; sing., phalanx, fā′langks; line of soldiers). There are three phalanges in each of the second through fifth fingers and two phalanges only in the thumb, also known as the pollex (pol′eks; thumb), for a total of 14 phalanges per hand. The proximal phalanx articulates with the head of a metacarpal, whereas the distal phalanx is the bone in the very tip of the finger. The middle phalanx of each finger lies between the proximal and distal phalanges; however, a middle phalanx is not present in the thumb.
Pronation (prō-nā′shŭn) of the forearm requires that the radius cross over the ulna and that both bones pivot along the interosseous membrane (figure 8.5e). When the forearm is pronated, the palm of the hand is facing posteriorly. Now pronate your own forearm; you can sometimes palpate the radius and feel it criss-crossing over the ulna. In this position, the head of the radius is still along the lateral side of the elbow, but the distal end of the radius has crossed over and is the more medial structure. When an individual has the upper limbs extended and forearms supinated, the bones of the forearm may angle laterally from the elbow joint. This positioning is referred to as the carrying angle of the elbow, and this angle measures about 5 to 15 degrees. The carrying angle positions the bones of the forearms such that the forearms will clear the hips during walking (and as the forearm bones swing during the process). Females have wider carrying angles than males, presumably because they have wider hips than males
The bones that form the wrist and hand are the carpals, metacarpals, and phalanges (figure 8.6). The carpals (kar′păl) are small, short bones that form the wrist. They are arranged roughly in two rows (a proximal row and a distal row) of four bones each. These small bones allow for the multiple movements possible at the wrist. The proximal row of carpal bones, listed from lateral to medial, are the scaphoid (skaf′oyd; skaphe = boat), lunate (lū′nāt; luna = moon), triquetrum (trī-kwē′trŭm; triquetrus = three-cornered), and pisiform (pis′i-fōrm; pisum = pea, forma = appearance). The bones of the distal row of carpal bones are the most laterally placed trapezium (tra-pē′zē-ŭm; trapeza = table), trapezoid (trap′ĕ-zoyd), capitate (kap′i-tāt; caput = head), and hamate
The bones that form the ankle and foot are the tarsals, metatarsals, and phalanges (figure 8.14). The seven tarsals (tar′săl; tarsus = flat surface) of the ankle and proximal foot are analogous to the eight carpal bones of the wrist, although their shapes and arrangement are different. The tarsal bones are thoroughly integrated into the structure of the foot because they help the ankle bear the body's weight.
The calcaneus, talus, and navicular are considered the proximal row of tarsal bones. The largest tarsal bone is the calcaneus (kal-kā′nē-ŭs; heel), which forms the heel. Its posterior end is a rough, knob-shaped projection that is the point of attachment for the calcaneal (Achilles) tendon extending from the strong muscles on the posterior side of the leg. The superiormost and second-largest tarsal bone is the talus (tā′lŭs; ankle bone). The superior aspect of the talus articulates with the articular surface of the tibia. The navicular (nă-vik′yū-lăr; navis = ship) bone is on the medial side of the ankle. The distal row is formed by a group of four tarsal bones. The three cuneiform (kū′ne-i-fōrm; cuneus = wedge) bones are wedge-shaped bones with articulations between them, positioned anterior to the navicular bone. They are named according to their position: medial cuneiform, intermediate cuneiform, and lateral cuneiform bones. The cuneiform bones articulate proximally with the anterior surface of the navicular bone. The laterally placed cuboid (kyū′boyd; kybos = cube) bone articulates at its medial surface with the lateral cuneiform and the calcaneus. The distal surfaces of the cuboid bone and the cuneiform bones articulate with the metatarsal bones of the foot.
Together, the bones of the humerus, radius, and ulna form the elbow joint (figure 8.4b, c). The medial and lateral epicondyles (ep′i-kon′dīl; epi = upon, kondylos = a knuckle) are bony side projections on the distal humerus that provide surfaces for muscle attachment. Palpate both sides of your elbow; the bumps you feel are the medial and lateral epicondyles. Traveling posterior to the medial epicondyle is the ulnar nerve (see section 16.4e), which supplies many intrinsic hand muscles.
The distal end of the humerus also has two smooth, curved surfaces for articulation with the bones of the forearm. The rounded capitulum (kă-pit′yū-lŭm; caput = head) is located laterally and articulates with the head of the radius. The pulley-shaped trochlea (trok′lē-ă; trochileia = a pulley) is located medially and articulates with the trochlear notch of the ulna. Additionally, the distal end of the humerus exhibits three depressions, two on its anterior surface and one on its posterior surface. The anterolaterally placed radial fossa accommodates the head of the radius, and the anteromedially placed coronoid (kōr′ŏ-noyd; korōnē = a crow, eidos = resembling) fossa accommodates the coronoid process of the ulna. The posterior depression called the olecranon (ō-lek′ră-non; olene = ulna, kranion = head) fossa accommodates the olecranon of the ulna when the elbow is extended.
The arrangement and numbers of bones in the lower limb are similar to those of the upper limb. However, because the bones of the lower limb are adapted for weight bearing and locomotion, they are shaped differently and articulate differently than the comparable bones of the upper limb. Each lower limb contains 30 bones: 1 femur, located in the femoral region 1 patella (kneecap), located in the patellar region 1 tibia and 1 fibula, located in the crural region 7 tarsal bones, which form the bones of the ankle and proximal foot 5 metatarsal bones, which form the arched part of the foot 14 phalanges, which form the toes
The femur (fē′mŭr; thigh) is the longest bone in the body as well as the strongest and heaviest (figure 8.11). The nearly spherical head of the femur articulates with the os coxae at the acetabulum. There is a small depression within the head of the femur, called the fovea (fō′vē-ă; a pit), or fovea capitis. Here a small ligament connects the head of the femur to the acetabulum. Distal to the head, an elongated, constricted neck joins the shaft of the femur at an angle. This results in a medial angling of the femur, which brings the knees closer to the midline.
The adult pelvis (pel′vis; pl., pelves, pel′vēz; basin) is composed of four bones: the sacrum, the coccyx, and the right and left ossa coxae (os′ă kok′să; sing., os coxae; hip bone) (figure 8.7). The pelvis protects and supports the viscera in the inferior part of the ventral body cavity. In contrast, the term pelvic girdle refers to Page 232the left and right ossa coxae only. The radiograph in figure 8.8 illustrates how the pelvis articulates with each bone of the thigh (femur). The head of each femur fits snugly into the acetabulum of each os coxae. When a person is standing upright, the pelvis is angled (or "tipped") slightly anteriorly. Each os coxae of the pelvic girdle is formed by the fusion of three bones: an ilium, an ischium, and a pubis. Diagrams and photos show the features of these bones and their relationships in (a) lateral and (b) medial views.
The os coxae is commonly referred to as the hip bone (and sometimes as the coxal bone or the innominate bone). Each os coxae is formed from three separate bones: the ilium, the ischium, and the pubis (figure 8.9). These three bones fuse between the ages of 13 and 15 years to form the single os coxae. Each os coxae articulates posteriorly with an auricular surface of the sacrum at the sacroiliac joint. The femur articulates with a deep, curved depression on the lateral surface of the os coxae called the acetabulum (as-ĕ-tab′yū-lŭm; shallow vinegar cup). The acetabulum contains a smooth curved surface, called the lunate surface, which is C-shaped and articulates with the femoral head. The three bones that form the os coxae (ilium, ischium, and pubis) all contribute a portion to the acetabulum. Thus, the acetabulum represents a region where these bones have fused.
ne benefit of space travel is that it has helped advance our knowledge of human anatomy. We are amazed by video showing astronauts in space running on treadmills, riding stationary bicycles, jumping rope, and doing various other exercises. For astronauts—as for all of us—exercise is essential for maintaining bone mass and strength as well as muscle tone and strength. When we exercise on Earth, our contracting muscles work with and against gravity applying stress to the bones to which they are attached, thereby strengthening the bone and ultimately preventing it from becoming thin and brittle. Regular exercise prevents degenerative changes in the skeleton and helps us avoid serious health problems later in life. When we exercise, we move the bones of the appendicular skeleton, which includes the bones of the upper and lower limbs, and the girdles of bones that hold and attach the upper and lower limbs to the axial skeleton (figure 8.1). The pectoral girdle consists of bones that hold the upper limbs in place, whereas the pelvic girdle consists of bones that hold the lower limbs in place. In this chapter, we examine the specific components of the appendicular skeleton and explore their interactions with other systems, such as the muscular and cardiovascular systems. Be sure to review figure 6.17 regarding bone markings before you proceed.
The pectoral (pek′tō-răl; pectus = breastbone) girdle (ger′dĕl) articulates with the trunk and supports the upper limbs. A pectoral girdle consists of the left and right clavicles (collarbones) and the left and right scapulae (shoulder blades). It is the attachment site for many muscles that move the upper limbs. The pectoral girdle promotes upper limb mobility in two ways: (1) Because the scapula is not directly attached to the axial skeleton, it moves freely across the posterior surface of the thorax, permitting the arm to move with it; and (2) the shallow cavity of the shoulder joint permits a wide range of movement of the upper limb.
The pubis (pyū′bis) fuses with the ilium and ischium at the acetabulum. The ischial ramus fuses anteriorly with the inferior pubic ramus to form the ischiopubic ramus (see figure 8.7). The superior pubic ramus originates at the anterior margin of the acetabulum. The obturator (ob′tū-rā′tŏr; obturo = to occlude) foramen is a space in the os coxae that is encircled by both pubic and ischial rami. A roughened ridge called the pubic crest is located on the anterosuperior surface of the superior ramus, and it ends at the pubic tubercle. The pubic tubercle is an attachment site for the inguinal ligament. A roughened area on the body of the pubis, called the symphysial (sim-fiz′ē-ăl; growing together) surface, or pubic symphysis, denotes the site of articulation between the pubic bones. On the medial surface of the pubis, the pectineal (pek-tin′ē-ăl; ridged or relating to the pubis) line originates and extends diagonally across the pubis to merge with the arcuate line.
The pelvic brim is a continuous oval ridge that extends from the pubic crest, pectineal line, and arcuate line to the rounded inferior edges of the sacral ala and promontory. This pelvic brim helps subdivide the entire pelvis into a true pelvis and a false pelvis (figure 8.10). The true pelvis, also known as the lesser pelvis, lies inferior to the pelvic brim. It encloses the pelvic cavity and forms a deep bowl that contains the pelvic organs. The false pelvis, also known as the greater pelvis, lies superior to the pelvic brim. It is enclosed by the ala of the iliac bones. It forms the inferior region of the abdominal cavity and houses the inferior abdominal organs.
The pelvic brim is the oval bony ridge that subdivides the pelvis into a true pelvis and a false pelvis. The pelvic inlet is the space enclosed by the pelvic brim, whereas the pelvic outlet is the inferior opening in the true pelvis. (a) Medial and anterolateral views of the true and false pelves. (b) Anterosuperior view of male and female pelves, demonstrating the sex differences between the pelvic inlet and outlet
The pelvis also has a superior and an inferior opening, and each has clinical significance. The pelvic inlet, also known as the superior pelvic aperture, is the superiorly positioned space enclosed by the pelvic brim. In other words, the pelvic brim is the bony oval ridge of bone, whereas the pelvic inlet is the space surrounded by the pelvic brim. The pelvic inlet is the opening at the boundary between the true pelvis and the false pelvis. The pelvic outlet, also known as the inferior pelvic aperture, is the inferiorly placed opening bounded by the coccyx, the ischial tuberosities, and the inferior border of the pubic symphysis. In males, the ischial spines sometimes project into the pelvic outlet, thereby narrowing the diameter of this outlet. In contrast, female ischial spines rarely project into the pelvic outlet. The pelvic outlet is covered with muscles and skin and forms the body region called the perineum (per′i-nē′ŭm). The width and size of the pelvic outlet is especially important in females, because the opening must be wide enough to accommodate the fetal head during childbirth.
Two massive, rough processes originate near the proximal end of the femur and serve as insertion sites for the powerful gluteal and thigh muscles. The greater trochanter (trō-kan′tĕr; a runner) projects laterally from the junction of the neck and shaft. Stand up and palpate your lateral thigh, near the hip joint; the bony projection you feel is the greater trochanter. A lesser trochanter is located on the femur's posteromedial surface. The greater and lesser trochanters are connected on the posterior surface of the femur by a thick oblique ridge of bone called the intertrochanteric (in′tĕr-trō′kan-ter′ik) crest. Anteriorly, a raised intertrochanteric line extends between Page 240the two trochanters and marks the distal edge of the hip joint capsule. Inferior to the intertrochanteric crest, the pectineal line marks the attachment of the pectineus muscle, whereas the gluteal (glŭ′tē-ăl; gloutos = buttock) tuberosity marks the attachment of the gluteus maximus muscle
The prominent feature on the posterior surface of the shaft is an elevated, midline ridge called the linea aspera (lin′ē-ă as′pĕr-ă; rough line). This ridge denotes the attachment site for many thigh muscles. The gluteal tuberosity and pectineal line merge proximally to the linea aspera. Distally, the linea aspera branches into medial and lateral supracondylar lines. A flattened triangular area, called the popliteal (pop-lit′ē-ăl; poples = ham of knee) surface, is bordered by these ridges and an imaginary line between the distal epicondyles. The medial supracondylar ridge terminates in the adductor tubercle, a rough, raised projection that is the site of attachment for the adductor magnus muscle. On the distal, inferior surface of the femur are two smooth, oval articulating surfaces called the medial and lateral condyles (kon′dīl). Superior to each condyle are projections called the medial and lateral epicondyle, respectively. When you flex your knee, you can palpate these epicondyles in the thigh on the sides of your knee joint. The medial and lateral supracondylar lines terminate at these epicondyles. On the distal posterior surface of the femur, a deep intercondylar fossa separates the two condyles. Both condyles continue from the posterior surface to the anterior surface, where their articular faces merge, producing an articular surface with elevated lateral borders. This smooth anteromedial depression, called the patellar surface, is the place where the patella articulates with the femur.
The clavicle (klav′i-kĕl; clavis = key) is an S-shaped bone that extends between the manubrium of the sternum and the acromion of the scapula (figure 8.2). It is the only direct connection between the pectoral girdle and the axial skeleton. Its sternal end (medial end) is roughly pyramidal in shape and articulates with the manubrium of the sternum, forming the sternoclavicular joint. The acromial end (lateral end) of the clavicle is broad and flattened. The acromial end articulates with the acromion of the scapula, forming the acromioclavicular joint. The superior surface of the clavicle is relatively smooth, but the inferior surface is marked by grooves and ridges for muscle and ligament attachments. On the inferior surface, near the acromial end, is a rough tuberosity called the conoid (kō′noyd; konoeides = cone-shaped) tubercle, the attachment site for the coracoclavicular ligament. The inferiorly located prominence at the sternal end of the clavicle is called the costal tuberosity, the attachment of the shoulder's costoclavicular ligament.
The scapula (skap′yū-lă) is a broad, flat, triangular bone (figure 8.3). You can palpate your scapula by putting your hand on your superolateral back region and moving your upper limb; the bone you feel moving is the scapula. Several large projections extend from the scapula and provide surface area for muscle and ligament attachments. The spine of the scapula is a ridge of bone on the posterior aspect of the scapula. It is easily palpated under the skin. The spine is continuous with a larger, posterior process called the acromion (ă-krō′mē-on; akron = tip, omos = shoulder), which forms the bony tip of the shoulder. Palpate the superior region of your shoulder; the prominent bump you feel is the acromion. The acromion articulates with the acromial end of the clavicle. The coracoid (kōr′ă-koyd; korakodes = like a crow's beak) process is the smaller, more anterior projection.
The radius and ulna are the bones of the forearm (figure 8.5). In anatomic position, these bones are parallel, and the radius (rā′dē-ŭs; spoke of a wheel, ray) is lateral. The proximal end of the radius has a distinctive disc-shaped head that articulates with the capitulum of the humerus. A narrow neck separates the radial head from the radial tuberosity (or bicipital tuberosity). The radial tuberosity is an attachment site for the biceps brachii muscle.
The shaft of the radius curves slightly and leads to a wide distal end where there is a laterally placed styloid (stī′loyd; stylos = pillar, post) process. This bony projection can be palpated on the lateral side of the wrist, just proximal to the thumb. On the distal medial surface of the radius is an ulnar notch, where the medial surface of the radius articulates with the distal end of the ulna (figure 8.5c). The ulna (ŭl′nă) is the longer, medially placed bone of the forearm. At the proximal end of the ulna, a C-shaped trochlear notch interlocks with the trochlea of the humerus. The posterosuperior aspect of the trochlear notch has a prominent projection called the olecranon. The olecranon articulates with the olecranon fossa of the humerus and forms the posterior "bump" of the elbow. (Palpate your posterior elbow; the bump you feel is the olecranon.) The inferior lip of the trochlear notch, called the coronoid process, articulates with the humerus at the coronoid fossa. Lateral to the coronoid process, a smooth, curved radial notch accommodates the head of the radius and helps form the proximal radioulnar joint (figure 8.5b). Also at the proximal end of this bone is the tuberosity of ulna. At the distal end of the ulna, the shaft narrows and terminates in a knoblike head that has a posteromedial styloid process. The styloid process of the ulna may be palpated on the medial ("little finger" side) of the wrist.
The largest of the three coxal bones is the ilium (il′ē-ŭm; groin, flank), which forms the superior region of the os coxae and the largest portion of the acetabular surface. The wide, fan-shaped portion of the ilium is called the ala (ā′lă; wing). The ala terminates inferiorly at a ridge called the arcuate line (ar′kyū-āt; arcuatus = bowed) on the medial surface of the ilium. On the medial side of the ala is a depression termed the iliac fossa. On the lateral surface of the ilium, anterior, posterior, and inferior gluteal lines are attachment sites for the gluteal muscles of the buttock (see section 12.2a). The posteromedial side of the ilium exhibits a large, roughened area called the auricular (aw-rik′yū-lăr; auris = ear) surface, where the ilium articulates with the sacrum at the sacroiliac joint.
The superiormost ridge of the ilium is the iliac crest. Palpate the posterosuperior edges of your hips; the ridge of bone you feel on each side is the iliac crest. The iliac crest arises anteriorly from a projection called the anterior superior iliac spine and extends posteriorly to the posterior superior iliac spine. Located inferiorly to the ala of the ilium are the anterior inferior iliac spine and the posterior inferior iliac spine. The posterior inferior iliac spine is adjacent to a prominent greater sciatic (sī-at′ik; sciaticus = hip joint) notch, through which the sciatic nerve travels to the lower limb (see section 16.4g). The ilium fuses with the ischium (is′kē-ŭm; ischion = hip) near the superior and posterior margins of the acetabulum. The ischium accounts for the posterior two-fifths of the acetabular surface. Posterior to the acetabulum, the prominent triangular ischial (is′kē-ăl) spine projects medially. The bulky bone superior to the ischial spine is called the ischial body. The lesser sciatic notch is a semicircular depression inferior to the ischial spine. The posterolateral border of the ischium is a roughened projection called the Page 233ischial tuberosity. The ischial tuberosities are also called the sitz bones by some health professionals and fitness instructors, because they support the weight of the body when seated. If you palpate your buttocks while in a sitting position, you can feel the large ischial tuberosities. An elongated ramus (rā′mŭs; pl., rami, rā′mī) of the ischium extends from the ischial tuberosity toward its anterior fusion with the pubis.
The tibia (tib′ē-ă; large shinbone) is medial and the only weight-bearing bone of the crural region. Its broad, superior head has two relatively flat surfaces, the medial and lateral condyles, which articulate with the medial and lateral condyles of the femur, respectively. Separating the medial and lateral condyles of the tibia is a prominent ridge called the intercondylar eminence (em′i-nens). On the proximal posterolateral side of the tibia is a fibular articular facet where the head of the fibula articulates to form the superior (or proximal) tibiofibular joint. The rough anterior surface of the tibia near the medial and lateral condyles is the tibial tuberosity, which can be palpated just inferior to the patella and marks the attachment site for the patellar ligament. The anterior border (or margin) is a ridge that extends distally along the anterior tibial surface from the tibial tuberosity. This crest can be readily felt through the skin and is commonly referred to as the shin.
The tibia narrows distally, but at its medial border, it forms a large, prominent process called the medial malleolus (ma-lē′ō-lŭs; malleus = hammer). Palpate the medial side of your ankle; the bump you feel is your medial malleolus. On the distal posterolateral side of the tibia is a fibular notch, where the fibula articulates and forms the inferior (or distal) tibiofibular joint. On the inferior distal surface of the tibia is the smooth inferior articular surface for the talus, one of the tarsal bones. The fibula (fib′yū-lă; buckle, clasp) is the long, thin, lateral bone of the leg. It has expanded proximal and distal ends. Although the fibula does not bear any weight, it is the origin for several muscles. The fibula articulates with the tibia at its proximal and distal ends. The rounded, knoblike head of the fibula is slightly inferior and posterior to the lateral condyle of the tibia. On the head, the smooth articular facet articulates with the tibia. Distal to the fibular head is Page 241the neck of the fibula, followed by its shaft. Although the fibula does not bear or transfer weight, its distal tip, called the lateral malleolus, extends laterally to the ankle joint, where it provides lateral stability. Palpate the lateral side of your ankle; the bump you feel is your lateral malleolus.
The scapula has several flattened regions of bone that provide surfaces for the attachment of some of the rotator cuff muscles, which help stabilize and move the shoulder joint. The broad, relatively smooth, anterior surface of the scapula is called the subscapular (sŭb-skap′yū-lăr; sub = under) fossa (fos′ă; pl., fossae, fos′ē). It is slightly concave and relatively featureless. A large muscle called the Page 225subscapularis overlies this fossa. The spine subdivides the posterior surface of the scapula into two shallow depressions, or fossae. The depression superior to the spine is the supraspinous (sū′pră-spı̄′nŭs; supra = above) fossa; inferior to the spine is a broad, extensive surface called the infraspinous fossa. The supraspinatus and infraspinatus muscles, respectively, occupy these fossae
The upper limb consists of the brachium (arm), antebrachium (forearm), and hand. The complex structure of the hand in particular gives humans capabilities beyond those of most other vertebrates. Each upper limb contains 30 bones: 1 humerus, located in the brachium region 1 radius and 1 ulna, located in the antebrachium region 8 carpal bones, which form the wrist 5 metacarpal bones, which form the palm of the hand 14 phalanges, which form the fingers
The humerus (hyū′mĕr-ŭs) is the longest and largest upper limb bone (figure 8.4). Its proximal end has a hemispherical head that articulates with the glenoid cavity of the scapula. Adjacent to the head are two tubercles. The prominent greater tubercle is positioned more laterally and helps form the rounded contour of the shoulder. The lesser tubercle is smaller and located more anteromedially. Between the two tubercles is the intertubercular sulcus (or bicipital sulcus, or bicipital groove), a depression that contains the tendon of the long head of the biceps brachii muscle
posterior views of the elbow joint, which is formed by the humerus articulating with the radius and ulna. Between the tubercles and the head of the humerus is the anatomical neck, an almost indistinct groove that marks the location of the former epiphyseal plate. The surgical neck is a narrowing of the bone immediately distal to the tubercles, at the transition from the head to the shaft. This feature is called the "surgical" neck because it is a common fracture site. The shaft of the humerus has a roughened area, termed the deltoid (del′toyd; deltoeides = like the Greek letter Δ) tuberosity (tū′bĕr-os′i-tē), which extends along its lateral surface for about half the length of the humerus. The deltoid muscle of the shoulder attaches to this roughened surface (see section 12.1b). The radial groove (or spiral groove) is located adjacent to the deltoid tuberosity and is where the radial nerve (see section 16.4e) and some blood vessels travel.