8: The Appendicular Skeleton
- Page ID
- 169025
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\( \newcommand{\dsum}{\displaystyle\sum\limits} \)
\( \newcommand{\dint}{\displaystyle\int\limits} \)
\( \newcommand{\dlim}{\displaystyle\lim\limits} \)
\( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)
( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\id}{\mathrm{id}}\)
\( \newcommand{\Span}{\mathrm{span}}\)
\( \newcommand{\kernel}{\mathrm{null}\,}\)
\( \newcommand{\range}{\mathrm{range}\,}\)
\( \newcommand{\RealPart}{\mathrm{Re}}\)
\( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)
\( \newcommand{\Argument}{\mathrm{Arg}}\)
\( \newcommand{\norm}[1]{\| #1 \|}\)
\( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)
\( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)
\( \newcommand{\vectorA}[1]{\vec{#1}} % arrow\)
\( \newcommand{\vectorAt}[1]{\vec{\text{#1}}} % arrow\)
\( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\( \newcommand{\vectorC}[1]{\textbf{#1}} \)
\( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)
\( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)
\( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)
\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)
\(\newcommand{\longvect}{\overrightarrow}\)
\( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)
\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Chapter Overview
The human appendicular skeleton consists of the limb bones and the girdles that anchor them to the axial skeleton, enabling movement, manipulation, and locomotion. It is composed of 126 bones organized into the pectoral (shoulder) girdles, upper limbs, pelvic (hip) girdle, and lower limbs.
Pectoral Girdle
The pectoral girdle, formed by the clavicle and scapula, attaches each upper limb to the axial skeleton while allowing a high degree of mobility. The clavicle links the sternum to the scapula, supports the upper limb, transmits forces to the trunk, and protects underlying neurovascular structures. The scapula lies on the posterior thorax and provides large surfaces and processes (such as the spine, acromion, coracoid process, and fossae) for muscle attachment and forms part of the glenohumeral joint via the glenoid cavity.
Bones of the Upper Limb: Arm, Forearm, and Hand
The upper limbs - including the humerus, radius, ulna, carpals, metacarpals, and phalanges - are specialized for precise, coordinated movements of the hands. Each upper limb has 30 bones divided into the arm, forearm, and hand. The humerus is the single bone of the arm, articulating proximally with the scapula and distally with the radius and ulna, and bearing tubercles, fossae, and epicondyles for articulation and muscle attachment. The forearm contains the medial ulna and lateral radius, which together form the elbow, radioulnar, and wrist articulations; they are linked by an interosseous membrane and terminate distally in styloid processes, with only the radius directly articulating with the carpal bones. The wrist contains eight carpals arranged in proximal and distal rows, forming the radiocarpal and midcarpal joints and the carpal tunnel. The palm is formed by five metacarpals, and the digits by 14 phalanges, with three phalanges in each finger and two in the thumb.
Pelvic Girdle and Pelvis: Bones, Landmarks, and Sexual Dimorphism
The pelvic girdle consists of the right and left hip bones, which unite anteriorly at the pubic symphysis and articulate posteriorly with the sacrum at the sacroiliac joints; together with the sacrum and coccyx, they form the pelvis. The pelvis supports body weight, transfers it to the lower limbs, and provides broad surfaces for muscle attachment. Each hip bone is formed by the ilium, ischium, and pubis, which fuse around the acetabulum, the socket of the hip joint. Major landmarks include the iliac crest and spines, the ischial tuberosity and spine, the pubic body and rami, the obturator foramen, and the greater and lesser sciatic notches and foramina. The pelvis is divided into greater (false) and lesser (true) pelves by the pelvic brim; the pelvic outlet forms its inferior opening. The female pelvis is wider, with a larger subpubic angle and broader greater sciatic notch, reflecting adaptation for childbirth.
Bones of the Lower Limb: Thigh, Leg, and Foot
The lower limbs - femur, tibia, fibula, tarsals, metatarsals, and phalanges - are adapted for support, balance, and efficient bipedal walking and running. Each lower limb also contains 30 bones, organized into the thigh, leg, and foot. The femur, the thigh bone, articulates proximally with the acetabulum and distally with the tibia and patella; its head, neck, trochanters, condyles, epicondyles, and shaft ridges provide sites for weight-bearing and muscle attachment. The patella, a sesamoid bone within a tendon, protects the anterior knee and improves mechanical leverage. The leg contains the weight‑bearing tibia medially and the slender fibula laterally, united by an interosseous membrane. The tibia articulates with the femur at the knee and forms the medial malleolus at the ankle, while the fibula contributes to lateral ankle stability via the lateral malleolus. The tarsal bones form the posterior foot and ankle, with the talus articulating with the tibia and fibula, and the calcaneus forming the heel; additional tarsals (navicular, cuneiforms, cuboid) link to the five metatarsals. The toes have a similar phalangeal pattern to the fingers, with three phalanges in each lesser toe and two in the great toe.
Embryologic Development and Ossification of Appendicular Bones
Developmentally, appendicular bones arise from mesenchyme in limb buds that appear in the fourth week of embryonic life. Limb growth is driven by the apical ectodermal ridge, with differentiation into hyaline cartilage models by the sixth week and limb rotation by the seventh week. Most appendicular bones ossify via endochondral ossification, beginning at primary ossification centers in the diaphyses around the twelfth fetal week, followed by secondary centers in the epiphyses. Epiphyseal plates between these centers enable lengthwise growth until they close and fuse in adulthood. The clavicle is an exception, forming primarily by intramembranous ossification beginning in the fifth week and continuing into early adulthood.
To achieve the chapter objectives, you are expected to actively engage with the material. Learning the tissues is not a passive process - your understanding will grow as you interact with the content, peers, and instructor, regularly checking your thinking against feedback and revisiting concepts until you can explain and apply them on your own.
By the end of this chapter, students should be able to:
- Compare the axial and appendicular skeletons, describing their major functions and components.
- Identify and locate the major bones of the pectoral girdle and upper limb, including clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, and phalanges, on diagrams, models, and the human body.
- Identify and locate the major bones of the pelvic girdle and lower limb, including hip (coxal) bones, femur, patella, tibia, fibula, tarsals, metatarsals, and phalanges, on diagrams, models, and the human body.
- Describe the key surface markings (bone features) of major appendicular bones (e.g., glenoid cavity, olecranon fossa, greater trochanter, medial malleolus) and relate them to muscle attachment, joint formation, or passage of nerves and vessels.
- Explain the structure and function of the pectoral and pelvic girdles, including how they articulate with the axial skeleton and how their structure supports mobility vs. stability.
- Describe the major joints of the upper and lower limbs (e.g., shoulder, elbow, wrist, hip, knee, ankle) and relate joint structure to range of motion.
- Trace the functional anatomy of the upper and lower limbs by relating bone structure to common movements (flexion, extension, abduction, adduction, rotation) at major joints.
- Compare biological male and biological female pelves, describing structural differences and their functional significance.
- Apply anatomical terminology (proximal/distal, medial/lateral, anterior/posterior) accurately when describing locations and relationships of appendicular bones.
- Relate clinical conditions or injuries (e.g., fractures of the clavicle, Colles’ fracture, hip fractures, knee injuries, flatfoot) to the underlying anatomy of the appendicular skeleton.
- 8.1: The Pectoral Girdle
- The appendicular skeleton includes all of the limb bones, plus the bones that unite each limb with the axial skeleton. The bones that attach each upper limb to the axial skeleton form the pectoral girdle (shoulder girdle). This consists of two bones, the scapula and clavicle. The clavicle (collarbone) is an S-shaped bone located on the anterior side of the shoulder. It is attached on its medial end to the sternum of the thoracic cage, which is part of the axial skeleton.
- 8.2: Bones of the Upper Limb
- The upper limb is divided into three regions. These consist of the arm, located between the shoulder and elbow joints; the forearm, which is between the elbow and wrist joints; and the hand, which is located distal to the wrist. There are 30 bones in each upper limb. The humerus is the single bone of the upper arm, and the ulna (medially) and the radius (laterally) are the paired bones of the forearm.
- 8.3: The Pelvic Girdle and Pelvis
- The pelvic girdle (hip girdle) is formed by a single bone, the hip bone or coxal bone (coxal = “hip”), which serves as the attachment point for each lower limb. Each hip bone, in turn, is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left hip bones also converge anteriorly to attach to each other. The bony pelvis is the entire structure formed by the two hip bones, the sacrum, and, attached inferiorly to the sacrum, the coccyx .
- 8.4: Bones of the Lower Limb
- Like the upper limb, the lower limb is divided into three regions. The thigh is that portion of the lower limb located between the hip joint and knee joint. The leg is specifically the region between the knee joint and the ankle joint. Distal to the ankle is the foot. The lower limb contains 30 bones. These are the femur, patella, tibia, fibula, tarsal bones, metatarsal bones, and phalanges.
Thumbnail: Appendicular skeleton of the human body. (CC BY-SC 4.0; via LibreTexts Biology).