Lower Limb

The number and arrangement of bones in the lower limb are similar to those of the upper limb. In the lower limb, however, they are adapted for weight-bearing and locomotion and are therefore shaped and articulated differently. The lower limb is divided into four regions containing a total of 30 bones per limb:

1. The femoral region, or thigh, extends from hip to knee and contains the femur (the longest bone in the body). The patella (kneecap) is a sesamoid bone at the junction of the femoral and crural regions.

Table 8.8 Comparison of the Male and Female Pelves

General Appearance Tilt

Ilium, greater pelvis Lesser Pelvis Sacrum Coccyx

Width of Greater Pelvis Pelvic Inlet Pelvic Outlet Greater Sciatic Notch Obturator Foramen Acetabulum Pubic arch

Male

More massive; rougher; heavier processes

Upper end of pelvis relatively vertical

Deeper; projects farther above sacroiliac joint

Narrower and deeper

Narrower and longer

Less movable; more vertical

Anterior superior spines closer together, hips less flared

Heart-shaped

Smaller

Narrower

Round

Faces more laterally, larger Usually 90° or less

Female

Less massive; smoother; more delicate processes

Upper end of pelvis tilted forward

Shallower; does not project as far above sacroiliac joint

Wider and shallower

Shorter and wider

More movable; tilted dorsally

Anterior superior spines farther apart; hips more flared

Round or oval

Larger

Wider

Triangular to oval

Faces slightly ventrally, smaller

Usually greater than 100°

Male And Female Greater Sciatic Notch
Figure 8.37 Comparison of the Male and Female Pelvic Girdles.

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2. The crural (CROO-rul) region, or leg proper, extends from knee to ankle and contains two bones, the medial tibia and lateral fibula.

3. The tarsal region (tarsus), or ankle, is the union of the crural region with the foot. The tarsal bones are treated as part of the foot.

4. The pedal region (pes), or foot, is composed of 7 tarsal bones, 5 metatarsals, and 14 phalanges in the toes.

Femur

The femur (FEE-mur) (fig. 8.38) has a nearly spherical head that articulates with the acetabulum of the pelvis, forming a quintessential ball-and-socket joint. A ligament extends from the acetabulum to a pit, the fovea capitis67 (FOE-vee-uh CAP-ih-tiss), in the head of the femur. Distal to the head is a constricted neck and then two massive, rough processes called the greater and lesser trochanters (tro-CAN-turs), which are insertions for the powerful muscles of the hip. They are connected on the posterior side by a thick oblique ridge of bone, the intertrochanteric crest, and on the anterior side by a more delicate intertrochanteric line.

The primary feature of the shaft is a posterior ridge called the linea aspera68 (LIN-ee-uh ASS-peh-ruh) at its midpoint. It branches into less conspicuous lateral and medial ridges at its inferior and superior ends.

The distal end of the femur flares into medial and lateral epicondyles, which serve as sites of muscle and ligament attachment. Distal to these are two smooth round surfaces of the knee joint, the medial and lateral condyles, separated by a groove called the intercondylar (IN-tur-CON-dih-lur) fossa. On the anterior side of the femur, a smooth medial depression called the patellar surface articulates with the patella.

Patella

The patella,69 or kneecap (fig. 8.38), is a roughly triangular sesamoid bone that forms within the tendon of the knee as a child begins to walk. It has a broad superior base, a pointed inferior apex, and a pair of shallow articular facets on its posterior surface where it articulates with the femur. The lateral facet is usually larger than the medial. The quadriceps femoris tendon extends from the anterior muscle of the thigh (the quadriceps femoris) to the patella, and it continues as the patellar ligament from the patella to the tibia.

Tibia

The leg has two bones—a thick, strong tibia (TIB-ee-uh) and a slender, lateral fibula (FIB-you-luh) (fig. 8.39). The

Chapter 8 The Skeletal System 281

tibia, on the medial side, is the only weight-bearing bone of the crural region. Its broad superior head has two fairly flat articular surfaces, the medial and lateral condyles, separated by a ridge called the intercondylar eminence. The condyles of the tibia articulate with those of the femur. The rough anterior surface of the tibia, the tibial tuberosity, can be palpated just below the patella. This is where the patellar ligament inserts and the thigh muscles exert their pull when they extend the leg. Distal to this, the shaft has a sharply angular anterior crest, which can be palpated in the shin. At the ankle, just above the rim of a standard dress shoe, you can palpate a prominent bony knob on each side. These are the medial and lateral malleoli70 (MAL-ee-OH-lie). The medial malleolus is part of the tibia, and the lateral malleolus is the part of the fibula.

Fibula

The fibula (fig. 8.39) is a slender lateral strut that helps to stabilize the ankle. It does not bear any of the body's weight; indeed, orthopedic surgeons sometimes remove the fibula and use it to replace damaged or missing bone elsewhere in the body. The fibula is somewhat thicker and broader at its proximal end, the head, than at the distal end. The point of the head is called the apex. The distal expansion is the lateral malleolus.

Like the radius and ulna, the tibia and fibula are joined by an interosseous membrane along their shafts.

The Ankle and Foot

The tarsal bones of the ankle are arranged in proximal and distal groups somewhat like the carpal bones of the wrist (fig. 8.40). Because of the load-bearing role of the ankle, however, their shapes and arrangement are conspicuously different from those of the carpal bones, and they are thoroughly integrated into the structure of the foot. The largest tarsal bone is the calcaneus71 (cal-CAY-nee-us), which forms the heel. Its posterior end is the point of attachment for the calcaneal (Achilles) tendon from the calf muscles. The second-largest tarsal bone, and the most superior, is the talus. It has three articular surfaces: an inferoposterior one that articulates with the calcaneus, a superior trochlear surface that articulates with the tibia, and an anterior surface that articulates with a short, wide tarsal bone called the navicular. The talus, calcaneus, and navicular are considered the proximal row of tarsal bones. (Navicular is also used as a synonym for the scaphoid bone of the wrist.)

The distal group forms a row of four bones. Proceeding from the medial side to the lateral, these are the medial,

67 fovea = pit + capitis = of the head 68linea = line + asper = rough 69 pat = pan + ella = little

70malle = hammer + olus = little 71 calc = stone, chalk

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282 Part Two Support and Movement

282 Part Two Support and Movement

Femur And Patella Anterior View
Figure 8.38 The Right Femur and Patella. (a) Anterior view; (fa) posterior view.

intermediate, and lateral cuneiforms72 (cue-NEE-ih-forms) and the cuboid. The cuboid is the largest.

The remaining bones of the foot are similar in arrangement and name to those of the hand. The proximal metatarsals73 are similar to the metacarpals. They are metatarsals I to V from medial to lateral, metatarsal I being proximal to the great toe. (Note that Roman numeral I represents the medial group of bones in the foot but the lateral group in the hand. In both cases, however, Roman numeral I refers to the largest digit of the limb.) Metatarsals I to III articulate with the first through third cuneiforms; metatarsals IV and V both articulate with the cuboid.

72cunei = wedge + form = in the shape of

73meta = beyond + tars = ankle

Bones of the toes, like those of the fingers, are called phalanges. The great toe is the hallux and contains only two bones, the proximal and distal phalanx I. The other toes each contain a proximal, middle, and distal phalanx. The metatarsal and phalangeal bones each have a base, body, and head, like the bones of the hand. All of them, especially the phalanges, are slightly concave on the ventral side.

The sole of the foot normally does not rest flat on the ground; rather, it has three springy arches that absorb the stress of walking (fig. 8.41). The medial longitudinal arch, which essentially extends from heel to hallux, is formed from the calcaneus, talus, navicular, cuneiforms, and metatarsals I to III. The lateral longitudinal arch extends from heel to little toe and includes the calcaneus, cuboid, and metatarsals IV and V. The transverse arch includes the cuboid, cuneiforms, and proximal heads of the

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Tibia And Fibula Posterior View

Figure 8.39 The Right Tibia and Fibula. (a) Anterior view; (b) posterior view. Why is the distal end of the tibia broader than that of the fibula?

Figure 8.39 The Right Tibia and Fibula. (a) Anterior view; (b) posterior view. Why is the distal end of the tibia broader than that of the fibula?

Distal phalanx -

Proximal phalanx-

First metatarsal -

Medial cuneiform-

Intermediate cuneiform

Lateral cuneiform-

Navicular-

Talus-

Trochlear surface -of talus

Medial cuneiform-

Intermediate cuneiform

Lateral cuneiform-

Navicular-

Trochlear Surface Talus

- Fifth metatarsal -

Tuberosity of calcaneus (b)

- Fifth metatarsal -

Head Fifth Metatarsal

Head Shaft

Base

Head Shaft

Base

Phalanges

Metatarsals

Tarsals

Figure 8.40 The Right Foot. (a) Superior view; (b) inferior view.

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

284 Part Two Support and Movement metatarsals. These arches are held together by short, strong ligaments. Excessive weight, repetitious stress, or congenital weakness of these ligaments can stretch them, resulting in pes planis (commonly called flat feet or fallen arches). This condition makes a person less tolerant of prolonged standing and walking. A comparison of the flat-footed apes with humans underscores the significance of the human foot arches (see insight 8.5, p. 286).

Table 8.9 summarizes the pelvic girdle and lower limb.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

19. Name the bones of the adult pelvic girdle. What three bones of a child fuse to form the os coxae of an adult?

20. Name any four structures of the pelvis that you can palpate and describe where to palpate them.

21. What parts of the femur are involved in the hip joint? What parts are involved in the knee joint?

22. Name the prominent knobs on each side of your ankle. What bones contribute to these structures?

23. Name all the bones that articulate with the talus and describe the location of each.

Fibula

Foot Anatomy Talus Calcaneus Angle

Fibula

Apex Fibuly

Metatarsal I

Proximal phalanx I

Metatarsal I

Proximal phalanx I

Distal phalanx I

Figure 8.41 Arches of the Foot. (a) Inferior view of the right foot. (b) X ray of the right foot, lateral view, showing the lateral longitudinal arch.

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Chapter 8 The Skeletal System 285

Table 8.9 Anatomical Checklist for the Pelvic Girdle and Lower Limb

Pelvic Girdle

Table 8.9 Anatomical Checklist for the Pelvic Girdle and Lower Limb

Pelvic Girdle

Os Coxae (tigs. 8.35 and 8.36)

Ilium—(Cont.)

Pubic symphysis

Greater sciatic notch

Greater (false) pelvis

Iliac pillar

Lesser (true) pelvis

Iliac fossa

Pelvic brim

Auricular surface

Pelvic inlet

Ischium

Pelvic outlet

Body

Acetabulum

Ischial spine

Obturator foramen

Lesser sciatic notch

Ilium

Ischial tuberosity

Iliac crest

Ramus

Anterior superior spine

Pubis

Anterior inferior spine

Superior ramus

Posterior superior spine

Inferior ramus

Posterior inferior spine

Body

Lower Limb

Femur (tig. 8.38)

Tibia (tig. 8.39)—(Cont.)

Proximal end

Anterior crest

Head

Medial malleolus

Fovea capitis

Fibula (fig. 8.39)

Neck

Head

Greater trochanter

Apex (styloid process)

Lesser trochanter

Lateral malleolus

Intertrochanteric crest

Tarsal Bones ((ig. 8.40)

Intertrochanteric line

Proximal group

Shaft

Calcaneus

Linea aspera

Talus

Distal end

Navicular

Medial condyle

Distal group

Lateral condyle

Medial cuneiform

Intercondylar fossa

Intermediate cuneiform

Medial epicondyle

Lateral cuneiform

Lateral epicondyle

Cuboid

Patellar surface

Bones o( the Foot (figs. 8.40 and 8.41)

Patella (fig. 8.38)

Metatarsal bones I-V

Base

Phalanges

Apex

Proximal phalanx

Articular facets

Middle phalanx

Tibia (fig. 8.39)

Distal phalanx

Medial condyle

Arches of the foot

Lateral condyle

Medial longitudinal arch

Intercondylar eminence

Lateral longitudinal arch

Tibial tuberosity

Transverse arch

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286 Part Two Support and Movement

Insight 8.5 Evolutionary Medicine

Skeletal Adaptations for Bipedalism

Some mammals can stand, hop, or walk briefly on their hind legs, but humans are the only mammals that are habitually bipedal. Footprints preserved in a layer of volcanic ash in Tanzania indicate that hominids walked upright as early as 3.6 million years ago. This bipedal locomotion is possible only because of several adaptations of the human feet, legs, spine, and skull (fig. 8.42). These features are so distinctive that pale-oanthropologists (those who study human fossil remains) can tell with considerable certainty whether a fossil species was able to walk upright.

As important as the hand has been to human evolution, the foot may be an even more significant adaptation. Unlike other mammals, humans support their entire body weight on two feet. While apes are flat-footed, humans have strong, springy foot arches that absorb shock as the body jostles up and down during walking and running. The tarsal bones are tightly articulated with each other, and the calcaneus is strongly developed. The hallux (great toe) is not opposable as it is in most Old World monkeys and apes, but it is highly developed so that it provides the "toe-off" that pushes the body forward in the last phase of the stride. For this reason, loss of the hallux has a more crippling effect than the loss of any other toe.

While the femurs of apes are nearly vertical, in humans they angle medially from the hip to the knee. This places our knees closer together, beneath the body's center of gravity. We lock our knees when standing, allowing us to maintain an erect posture with little muscular effort. Apes cannot do this, and they cannot stand on two legs for very long without tiring—much as you would if you tried to maintain an erect posture with your knees slightly bent.

In apes and other quadrupedal (four-legged) mammals, the abdominal viscera are supported by the muscular wall of the abdomen. In humans, the viscera bear down on the floor of the pelvic cavity, and a bowl-shaped pelvis is necessary to support their weight. This has resulted in a narrower pelvic outlet—a condition quite incompatible with the fact that we, including our infants, are such a large-brained species. The pain of childbirth is unique to humans and, one might say, a price we must pay for having both a large brain and a bipedal stance.

The largest muscle of the buttock, the gluteus maximus, serves in apes primarily as an abductor of the thigh—that is, it moves the leg lat-

Bipedalism Adaptations

Figure 8.42 Skeletal Adaptations for Bipedalism. These adaptations are best understood by comparison to our close living relative, the chimpanzee, which is not adapted for a comfortable or sustained erect stance. (a) The great toe (hallux) is adapted for grasping in apes and for striding and "toe-off" in humans. (fa) The femur is nearly vertical in apes but angles medially in humans, which places the knees under the center of gravity. (c) The os coxae is shortened and more bowl-like in humans than in apes. The iliac crest is expanded posteriorly and the sciatic notch is deeper in humans.

Figure 8.42 Skeletal Adaptations for Bipedalism. These adaptations are best understood by comparison to our close living relative, the chimpanzee, which is not adapted for a comfortable or sustained erect stance. (a) The great toe (hallux) is adapted for grasping in apes and for striding and "toe-off" in humans. (fa) The femur is nearly vertical in apes but angles medially in humans, which places the knees under the center of gravity. (c) The os coxae is shortened and more bowl-like in humans than in apes. The iliac crest is expanded posteriorly and the sciatic notch is deeper in humans.

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Chapter 8 The Skeletal System 287

Bipedal Locomotion Occipital Femur

Figure 8.42 Skeletal Adaptations for Bipedalism (continued). (d) In humans, the gluteus medius and minimus help to balance the body weight over one leg when the other leg is lifted from the ground. (e) The curvature of the human spine centers the body's weight over the pelvis, so humans can stand more effortlessly than apes. (f) The foramen magnum is shifted ventrally and the face is flatter in humans; thus the skull is balanced on the vertebral column and the gaze is directed forward when a person is standing.

Figure 8.42 Skeletal Adaptations for Bipedalism (continued). (d) In humans, the gluteus medius and minimus help to balance the body weight over one leg when the other leg is lifted from the ground. (e) The curvature of the human spine centers the body's weight over the pelvis, so humans can stand more effortlessly than apes. (f) The foramen magnum is shifted ventrally and the face is flatter in humans; thus the skull is balanced on the vertebral column and the gaze is directed forward when a person is standing.

erally. In humans, however, the ilium has expanded posteriorly, so the gluteus maximus originates behind the hip joint. This changes the function of the muscle—instead of abducting the thigh, it pulls the thigh back in the second half of a stride (pulling back on your right thigh, for example, when your left foot is off the ground and swinging forward). This action accounts for the smooth, efficient stride of a human as compared to the awkward, shuffling gait of a chimpanzee or gorilla when it is walking upright. The posterior growth of the ilium is the reason the greater sciatic notch is so deeply concave.

The lumbar curvature of the human spine allows for efficient bipedalism by shifting the body's center of gravity to the rear, above and slightly behind the hip joint. Because of their C-shaped spines, chimpanzees cannot stand as easily. Their center of gravity is anterior to the hip joint when they stand; they must exert a continual muscular effort to keep from falling forward, and fatigue sets in relatively quickly. Humans, by contrast, require little muscular effort to keep their balance. Our australopithecine ancestors probably could travel all day with relatively little fatigue.

The human head is balanced on the vertebral column with the gaze directed forward. The cervical curvature of the spine and remodeling of the skull have made this possible. The foramen magnum has moved to a more inferior location, and the face is much flatter than in an ape, so there is less weight anterior to the occipital condyles. Being balanced on the spine, the head does not require strong muscular attachments to hold it erect. Apes have prominent supraorbital ridges for the attachment of muscles that pull back on the skull. In humans these ridges are much lighter and the muscles of the forehead serve only for facial expression, not to hold the head up.

The forelimbs of apes are longer than the hindlimbs; indeed, some species such as the orangutan and gibbons hold their long forelimbs over their heads when they walk on their hind legs. By contrast, our arms are shorter than our legs and far less muscular than the forelimbs of apes. No longer needed for locomotion, our forelimbs have become better adapted for carrying objects, holding things closer to the eyes, and manipulating them more precisely.

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Responses

  • julia
    Where is the articular facet for patella of the right femur?
    7 years ago
  • gregory lopez
    How to palpate gluteus maximus?
    7 years ago
  • venla
    Which is the proximal bone of the lower limb?
    7 years ago
  • Miranda Mugwort
    Which is longer the tibia or fibula?
    7 years ago
  • FLORENCE
    What system is tibia in?
    7 years ago
  • Faramir
    WHERE IS THE SCIATIC NOTCH AREA?
    6 years ago
  • Billy
    Why is the breadth of the pelvic inlet important in telling us about a species?
    5 years ago

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