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  1. Preface
  2. Unit 1: Levels of Organization
    1. 1 An Introduction to the Human Body
      1. Introduction
      2. 1.1 Overview of Anatomy and Physiology
      3. 1.2 Structural Organization of the Human Body
      4. 1.3 Functions of Human Life
      5. 1.4 Requirements for Human Life
      6. 1.5 Homeostasis
      7. 1.6 Anatomical Terminology
      8. 1.7 Medical Imaging
      9. Key Terms
      10. Chapter Review
      11. Interactive Link Questions
      12. Review Questions
      13. Critical Thinking Questions
    2. 2 The Chemical Level of Organization
      1. Introduction
      2. 2.1 Elements and Atoms: The Building Blocks of Matter
      3. 2.2 Chemical Bonds
      4. 2.3 Chemical Reactions
      5. 2.4 Inorganic Compounds Essential to Human Functioning
      6. 2.5 Organic Compounds Essential to Human Functioning
      7. Key Terms
      8. Chapter Review
      9. Interactive Link Questions
      10. Review Questions
      11. Critical Thinking Questions
    3. 3 The Cellular Level of Organization
      1. Introduction
      2. 3.1 The Cell Membrane
      3. 3.2 The Cytoplasm and Cellular Organelles
      4. 3.3 The Nucleus and DNA Replication
      5. 3.4 Protein Synthesis
      6. 3.5 Cell Growth and Division
      7. 3.6 Cellular Differentiation
      8. Key Terms
      9. Chapter Review
      10. Interactive Link Questions
      11. Review Questions
      12. Critical Thinking Questions
    4. 4 The Tissue Level of Organization
      1. Introduction
      2. 4.1 Types of Tissues
      3. 4.2 Epithelial Tissue
      4. 4.3 Connective Tissue Supports and Protects
      5. 4.4 Muscle Tissue and Motion
      6. 4.5 Nervous Tissue Mediates Perception and Response
      7. 4.6 Tissue Injury and Aging
      8. Key Terms
      9. Chapter Review
      10. Interactive Link Questions
      11. Review Questions
      12. Critical Thinking Questions
  3. Unit 2: Support and Movement
    1. 5 The Integumentary System
      1. Introduction
      2. 5.1 Layers of the Skin
      3. 5.2 Accessory Structures of the Skin
      4. 5.3 Functions of the Integumentary System
      5. 5.4 Diseases, Disorders, and Injuries of the Integumentary System
      6. Key Terms
      7. Chapter Review
      8. Interactive Link Questions
      9. Review Questions
      10. Critical Thinking Questions
    2. 6 Bone Tissue and the Skeletal System
      1. Introduction
      2. 6.1 The Functions of the Skeletal System
      3. 6.2 Bone Classification
      4. 6.3 Bone Structure
      5. 6.4 Bone Formation and Development
      6. 6.5 Fractures: Bone Repair
      7. 6.6 Exercise, Nutrition, Hormones, and Bone Tissue
      8. 6.7 Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems
      9. Key Terms
      10. Chapter Review
      11. Review Questions
      12. Critical Thinking Questions
    3. 7 Axial Skeleton
      1. Introduction
      2. 7.1 Divisions of the Skeletal System
      3. 7.2 The Skull
      4. 7.3 The Vertebral Column
      5. 7.4 The Thoracic Cage
      6. 7.5 Embryonic Development of the Axial Skeleton
      7. Key Terms
      8. Chapter Review
      9. Interactive Link Questions
      10. Review Questions
      11. Critical Thinking Questions
    4. 8 The Appendicular Skeleton
      1. Introduction
      2. 8.1 The Pectoral Girdle
      3. 8.2 Bones of the Upper Limb
      4. 8.3 The Pelvic Girdle and Pelvis
      5. 8.4 Bones of the Lower Limb
      6. 8.5 Development of the Appendicular Skeleton
      7. Key Terms
      8. Chapter Review
      9. Interactive Link Questions
      10. Review Questions
      11. Critical Thinking Questions
    5. 9 Joints
      1. Introduction
      2. 9.1 Classification of Joints
      3. 9.2 Fibrous Joints
      4. 9.3 Cartilaginous Joints
      5. 9.4 Synovial Joints
      6. 9.5 Types of Body Movements
      7. 9.6 Anatomy of Selected Synovial Joints
      8. 9.7 Development of Joints
      9. Key Terms
      10. Chapter Review
      11. Interactive Link Questions
      12. Review Questions
      13. Critical Thinking Questions
    6. 10 Muscle Tissue
      1. Introduction
      2. 10.1 Overview of Muscle Tissues
      3. 10.2 Skeletal Muscle
      4. 10.3 Muscle Fiber Contraction and Relaxation
      5. 10.4 Nervous System Control of Muscle Tension
      6. 10.5 Types of Muscle Fibers
      7. 10.6 Exercise and Muscle Performance
      8. 10.7 Cardiac Muscle Tissue
      9. 10.8 Smooth Muscle
      10. 10.9 Development and Regeneration of Muscle Tissue
      11. Key Terms
      12. Chapter Review
      13. Interactive Link Questions
      14. Review Questions
      15. Critical Thinking Questions
    7. 11 The Muscular System
      1. Introduction
      2. 11.1 Interactions of Skeletal Muscles, Their Fascicle Arrangement, and Their Lever Systems
      3. 11.2 Naming Skeletal Muscles
      4. 11.3 Axial Muscles of the Head, Neck, and Back
      5. 11.4 Axial Muscles of the Abdominal Wall, and Thorax
      6. 11.5 Muscles of the Pectoral Girdle and Upper Limbs
      7. 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs
      8. Key Terms
      9. Chapter Review
      10. Review Questions
      11. Critical Thinking Questions
  4. Unit 3: Regulation, Integration, and Control
    1. 12 The Nervous System and Nervous Tissue
      1. Introduction
      2. 12.1 Basic Structure and Function of the Nervous System
      3. 12.2 Nervous Tissue
      4. 12.3 The Function of Nervous Tissue
      5. 12.4 The Action Potential
      6. 12.5 Communication Between Neurons
      7. Key Terms
      8. Chapter Review
      9. Interactive Link Questions
      10. Review Questions
      11. Critical Thinking Questions
    2. 13 Anatomy of the Nervous System
      1. Introduction
      2. 13.1 The Embryologic Perspective
      3. 13.2 The Central Nervous System
      4. 13.3 Circulation and the Central Nervous System
      5. 13.4 The Peripheral Nervous System
      6. Key Terms
      7. Chapter Review
      8. Interactive Link Questions
      9. Review Questions
      10. Critical Thinking Questions
    3. 14 The Somatic Nervous System
      1. Introduction
      2. 14.1 Sensory Perception
      3. 14.2 Central Processing
      4. 14.3 Motor Responses
      5. Key Terms
      6. Chapter Review
      7. Interactive Link Questions
      8. Review Questions
      9. Critical Thinking Questions
    4. 15 The Autonomic Nervous System
      1. Introduction
      2. 15.1 Divisions of the Autonomic Nervous System
      3. 15.2 Autonomic Reflexes and Homeostasis
      4. 15.3 Central Control
      5. 15.4 Drugs that Affect the Autonomic System
      6. Key Terms
      7. Chapter Review
      8. Interactive Link Questions
      9. Review Questions
      10. Critical Thinking Questions
    5. 16 The Neurological Exam
      1. Introduction
      2. 16.1 Overview of the Neurological Exam
      3. 16.2 The Mental Status Exam
      4. 16.3 The Cranial Nerve Exam
      5. 16.4 The Sensory and Motor Exams
      6. 16.5 The Coordination and Gait Exams
      7. Key Terms
      8. Chapter Review
      9. Interactive Link Questions
      10. Review Questions
      11. Critical Thinking Questions
    6. 17 The Endocrine System
      1. Introduction
      2. 17.1 An Overview of the Endocrine System
      3. 17.2 Hormones
      4. 17.3 The Pituitary Gland and Hypothalamus
      5. 17.4 The Thyroid Gland
      6. 17.5 The Parathyroid Glands
      7. 17.6 The Adrenal Glands
      8. 17.7 The Pineal Gland
      9. 17.8 Gonadal and Placental Hormones
      10. 17.9 The Endocrine Pancreas
      11. 17.10 Organs with Secondary Endocrine Functions
      12. 17.11 Development and Aging of the Endocrine System
      13. Key Terms
      14. Chapter Review
      15. Interactive Link Questions
      16. Review Questions
      17. Critical Thinking Questions
  5. Unit 4: Fluids and Transport
    1. 18 The Cardiovascular System: Blood
      1. Introduction
      2. 18.1 An Overview of Blood
      3. 18.2 Production of the Formed Elements
      4. 18.3 Erythrocytes
      5. 18.4 Leukocytes and Platelets
      6. 18.5 Hemostasis
      7. 18.6 Blood Typing
      8. Key Terms
      9. Chapter Review
      10. Interactive Link Questions
      11. Review Questions
      12. Critical Thinking Questions
    2. 19 The Cardiovascular System: The Heart
      1. Introduction
      2. 19.1 Heart Anatomy
      3. 19.2 Cardiac Muscle and Electrical Activity
      4. 19.3 Cardiac Cycle
      5. 19.4 Cardiac Physiology
      6. 19.5 Development of the Heart
      7. Key Terms
      8. Chapter Review
      9. Interactive Link Questions
      10. Review Questions
      11. Critical Thinking Questions
    3. 20 The Cardiovascular System: Blood Vessels and Circulation
      1. Introduction
      2. 20.1 Structure and Function of Blood Vessels
      3. 20.2 Blood Flow, Blood Pressure, and Resistance
      4. 20.3 Capillary Exchange
      5. 20.4 Homeostatic Regulation of the Vascular System
      6. 20.5 Circulatory Pathways
      7. 20.6 Development of Blood Vessels and Fetal Circulation
      8. Key Terms
      9. Chapter Review
      10. Interactive Link Questions
      11. Review Questions
      12. Critical Thinking Questions
    4. 21 The Lymphatic and Immune System
      1. Introduction
      2. 21.1 Anatomy of the Lymphatic and Immune Systems
      3. 21.2 Barrier Defenses and the Innate Immune Response
      4. 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types
      5. 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies
      6. 21.5 The Immune Response against Pathogens
      7. 21.6 Diseases Associated with Depressed or Overactive Immune Responses
      8. 21.7 Transplantation and Cancer Immunology
      9. Key Terms
      10. Chapter Review
      11. Interactive Link Questions
      12. Review Questions
      13. Critical Thinking Questions
  6. Unit 5: Energy, Maintenance, and Environmental Exchange
    1. 22 The Respiratory System
      1. Introduction
      2. 22.1 Organs and Structures of the Respiratory System
      3. 22.2 The Lungs
      4. 22.3 The Process of Breathing
      5. 22.4 Gas Exchange
      6. 22.5 Transport of Gases
      7. 22.6 Modifications in Respiratory Functions
      8. 22.7 Embryonic Development of the Respiratory System
      9. Key Terms
      10. Chapter Review
      11. Interactive Link Questions
      12. Review Questions
      13. Critical Thinking Questions
    2. 23 The Digestive System
      1. Introduction
      2. 23.1 Overview of the Digestive System
      3. 23.2 Digestive System Processes and Regulation
      4. 23.3 The Mouth, Pharynx, and Esophagus
      5. 23.4 The Stomach
      6. 23.5 The Small and Large Intestines
      7. 23.6 Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder
      8. 23.7 Chemical Digestion and Absorption: A Closer Look
      9. Key Terms
      10. Chapter Review
      11. Interactive Link Questions
      12. Review Questions
      13. Critical Thinking Questions
    3. 24 Metabolism and Nutrition
      1. Introduction
      2. 24.1 Overview of Metabolic Reactions
      3. 24.2 Carbohydrate Metabolism
      4. 24.3 Lipid Metabolism
      5. 24.4 Protein Metabolism
      6. 24.5 Metabolic States of the Body
      7. 24.6 Energy and Heat Balance
      8. 24.7 Nutrition and Diet
      9. Key Terms
      10. Chapter Review
      11. Review Questions
      12. Critical Thinking Questions
    4. 25 The Urinary System
      1. Introduction
      2. 25.1 Physical Characteristics of Urine
      3. 25.2 Gross Anatomy of Urine Transport
      4. 25.3 Gross Anatomy of the Kidney
      5. 25.4 Microscopic Anatomy of the Kidney
      6. 25.5 Physiology of Urine Formation
      7. 25.6 Tubular Reabsorption
      8. 25.7 Regulation of Renal Blood Flow
      9. 25.8 Endocrine Regulation of Kidney Function
      10. 25.9 Regulation of Fluid Volume and Composition
      11. 25.10 The Urinary System and Homeostasis
      12. Key Terms
      13. Chapter Review
      14. Review Questions
      15. Critical Thinking Questions
    5. 26 Fluid, Electrolyte, and Acid-Base Balance
      1. Introduction
      2. 26.1 Body Fluids and Fluid Compartments
      3. 26.2 Water Balance
      4. 26.3 Electrolyte Balance
      5. 26.4 Acid-Base Balance
      6. 26.5 Disorders of Acid-Base Balance
      7. Key Terms
      8. Chapter Review
      9. Interactive Link Questions
      10. Review Questions
      11. Critical Thinking Questions
  7. Unit 6: Human Development and the Continuity of Life
    1. 27 The Reproductive System
      1. Introduction
      2. 27.1 Anatomy and Physiology of the Male Reproductive System
      3. 27.2 Anatomy and Physiology of the Female Reproductive System
      4. 27.3 Development of the Male and Female Reproductive Systems
      5. Key Terms
      6. Chapter Review
      7. Interactive Link Questions
      8. Review Questions
      9. Critical Thinking Questions
    2. 28 Development and Inheritance
      1. Introduction
      2. 28.1 Fertilization
      3. 28.2 Embryonic Development
      4. 28.3 Fetal Development
      5. 28.4 Maternal Changes During Pregnancy, Labor, and Birth
      6. 28.5 Adjustments of the Infant at Birth and Postnatal Stages
      7. 28.6 Lactation
      8. 28.7 Patterns of Inheritance
      9. Key Terms
      10. Chapter Review
      11. Interactive Link Questions
      12. Review Questions
      13. Critical Thinking Questions
  8. References
  9. Index

8.1 The Pectoral Girdle

The pectoral girdle, consisting of the clavicle and the scapula, attaches each upper limb to the axial skeleton. The clavicle is an anterior bone whose sternal end articulates with the manubrium of the sternum at the sternoclavicular joint. The sternal end is also anchored to the first rib by the costoclavicular ligament. The acromial end of the clavicle articulates with the acromion of the scapula at the acromioclavicular joint. This end is also anchored to the coracoid process of the scapula by the coracoclavicular ligament, which provides indirect support for the acromioclavicular joint. The clavicle supports the scapula, transmits the weight and forces from the upper limb to the body trunk, and protects the underlying nerves and blood vessels.

The scapula lies on the posterior aspect of the pectoral girdle. It mediates the attachment of the upper limb to the clavicle, and contributes to the formation of the glenohumeral (shoulder) joint. This triangular bone has three sides called the medial, lateral, and superior borders. The suprascapular notch is located on the superior border. The scapula also has three corners, two of which are the superior and inferior angles. The third corner is occupied by the glenoid cavity. Posteriorly, the spine separates the supraspinous and infraspinous fossae, and then extends laterally as the acromion. The subscapular fossa is located on the anterior surface of the scapula. The coracoid process projects anteriorly, passing inferior to the lateral end of the clavicle.

8.2 Bones of the Upper Limb

Each upper limb is divided into three regions and contains a total of 30 bones. The upper arm is the region located between the shoulder and elbow joints. This area contains the humerus. The proximal humerus consists of the head, which articulates with the scapula at the glenohumeral joint, the greater and lesser tubercles separated by the intertubercular (bicipital) groove, and the anatomical and surgical necks. The humeral shaft has the roughened area of the deltoid tuberosity on its lateral side. The distal humerus is flattened, forming a lateral supracondylar ridge that terminates at the small lateral epicondyle. The medial side of the distal humerus has the large, medial epicondyle. The articulating surfaces of the distal humerus consist of the trochlea medially and the capitulum laterally. Depressions on the humerus that accommodate the forearm bones during bending (flexing) and straightening (extending) of the elbow include the coronoid fossa, the radial fossa, and the olecranon fossa.

The forearm is the region of the upper limb located between the elbow and wrist joints. This region contains two bones, the ulna medially and the radius on the lateral (thumb) side. The elbow joint is formed by the articulation between the trochlea of the humerus and the trochlear notch of the ulna, plus the articulation between the capitulum of the humerus and the head of the radius. The proximal radioulnar joint is the articulation between the head of the radius and the radial notch of the ulna. The proximal ulna also has the olecranon process, forming an expanded posterior region, and the coronoid process and ulnar tuberosity on its anterior aspect. On the proximal radius, the narrowed region below the head is the neck; distal to this is the radial tuberosity. The shaft portions of both the ulna and radius have an interosseous border, whereas the distal ends of each bone have a pointed styloid process. The distal radioulnar joint is found between the head of the ulna and the ulnar notch of the radius. The distal end of the radius articulates with the proximal carpal bones, but the ulna does not.

The base of the hand is formed by eight carpal bones. The carpal bones are united into two rows of bones. The proximal row contains (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones. The scaphoid, lunate, and triquetrum bones contribute to the formation of the radiocarpal joint. The distal row of carpal bones contains (from medial to lateral) the hamate, capitate, trapezoid, and trapezium bones (“So Long To Pinky, Here Comes The Thumb”). The anterior hamate has a prominent bony hook. The proximal and distal carpal rows articulate with each other at the midcarpal joint. The carpal bones, together with the flexor retinaculum, also form the carpal tunnel of the wrist.

The five metacarpal bones form the palm of the hand. The metacarpal bones are numbered 1–5, starting with the thumb side. The first metacarpal bone is freely mobile, but the other bones are united as a group. The digits are also numbered 1–5, with the thumb being number 1. The fingers and thumb contain a total of 14 phalanges (phalanx bones). The thumb contains a proximal and a distal phalanx, whereas the remaining digits each contain proximal, middle, and distal phalanges.

8.3 The Pelvic Girdle and Pelvis

The pelvic girdle, consisting of a hip bone, serves to attach a lower limb to the axial skeleton. The hip bone articulates posteriorly at the sacroiliac joint with the sacrum, which is part of the axial skeleton. The right and left hip bones converge anteriorly and articulate with each other at the pubic symphysis. The combination of the hip bone, the sacrum, and the coccyx forms the pelvis. The pelvis has a pronounced anterior tilt. The primary function of the pelvis is to support the upper body and transfer body weight to the lower limbs. It also serves as the site of attachment for multiple muscles.

The hip bone consists of three regions: the ilium, ischium, and pubis. The ilium forms the large, fan-like region of the hip bone. The superior margin of this area is the iliac crest. Located at either end of the iliac crest are the anterior superior and posterior superior iliac spines. Inferior to these are the anterior inferior and posterior inferior iliac spines. The auricular surface of the ilium articulates with the sacrum to form the sacroiliac joint. The medial surface of the upper ilium forms the iliac fossa, with the arcuate line marking the inferior limit of this area. The posterior margin of the ilium has the large greater sciatic notch.

The posterolateral portion of the hip bone is the ischium. It has the expanded ischial tuberosity, which supports body weight when sitting. The ischial ramus projects anteriorly and superiorly. The posterior margin of the ischium has the shallow lesser sciatic notch and the ischial spine, which separates the greater and lesser sciatic notches.

The pubis forms the anterior portion of the hip bone. The body of the pubis articulates with the pubis of the opposite hip bone at the pubic symphysis. The superior margin of the pubic body has the pubic tubercle. The pubis is joined to the ilium by the superior pubic ramus, the superior surface of which forms the pectineal line. The inferior pubic ramus projects inferiorly and laterally. The pubic arch is formed by the pubic symphysis, the bodies of the adjacent pubic bones, and the two inferior pubic rami. The inferior pubic ramus joins the ischial ramus to form the ischiopubic ramus. The subpubic angle is formed by the medial convergence of the right and left ischiopubic rami.

The lateral side of the hip bone has the cup-like acetabulum, which is part of the hip joint. The large anterior opening is the obturator foramen. The sacroiliac joint is supported by the anterior and posterior sacroiliac ligaments. The sacrum is also joined to the hip bone by the sacrospinous ligament, which attaches to the ischial spine, and the sacrotuberous ligament, which attaches to the ischial tuberosity. The sacrospinous and sacrotuberous ligaments contribute to the formation of the greater and lesser sciatic foramina.

The broad space of the upper pelvis is the greater pelvis, and the narrow, inferior space is the lesser pelvis. These areas are separated by the pelvic brim (pelvic inlet). The inferior opening of the pelvis is the pelvic outlet. Compared to the male, the female pelvis is wider to accommodate childbirth, has a larger subpubic angle, and a broader greater sciatic notch.

8.4 Bones of the Lower Limb

The lower limb is divided into three regions. These are the thigh, located between the hip and knee joints; the leg, located between the knee and ankle joints; and distal to the ankle, the foot. There are 30 bones in each lower limb. These are the femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones, and 14 phalanges.

The femur is the single bone of the thigh. Its rounded head articulates with the acetabulum of the hip bone to form the hip joint. The head has the fovea capitis for attachment of the ligament of the head of the femur. The narrow neck joins inferiorly with the greater and lesser trochanters. Passing between these bony expansions are the intertrochanteric line on the anterior femur and the larger intertrochanteric crest on the posterior femur. On the posterior shaft of the femur is the gluteal tuberosity proximally and the linea aspera in the mid-shaft region. The expanded distal end consists of three articulating surfaces: the medial and lateral condyles, and the patellar surface. The outside margins of the condyles are the medial and lateral epicondyles. The adductor tubercle is on the superior aspect of the medial epicondyle.

The patella is a sesamoid bone located within a muscle tendon. It articulates with the patellar surface on the anterior side of the distal femur, thereby protecting the muscle tendon from rubbing against the femur.

The leg contains the large tibia on the medial side and the slender fibula on the lateral side. The tibia bears the weight of the body, whereas the fibula does not bear weight. The interosseous border of each bone is the attachment site for the interosseous membrane of the leg, the connective tissue sheet that unites the tibia and fibula.

The proximal tibia consists of the expanded medial and lateral condyles, which articulate with the medial and lateral condyles of the femur to form the knee joint. Between the tibial condyles is the intercondylar eminence. On the anterior side of the proximal tibia is the tibial tuberosity, which is continuous inferiorly with the anterior border of the tibia. On the posterior side, the proximal tibia has the curved soleal line. The bony expansion on the medial side of the distal tibia is the medial malleolus. The groove on the lateral side of the distal tibia is the fibular notch.

The head of the fibula forms the proximal end and articulates with the underside of the lateral condyle of the tibia. The distal fibula articulates with the fibular notch of the tibia. The expanded distal end of the fibula is the lateral malleolus.

The posterior foot is formed by the seven tarsal bones. The talus articulates superiorly with the distal tibia, the medial malleolus of the tibia, and the lateral malleolus of the fibula to form the ankle joint. The talus articulates inferiorly with the calcaneus bone. The sustentaculum tali of the calcaneus helps to support the talus. Anterior to the talus is the navicular bone, and anterior to this are the medial, intermediate, and lateral cuneiform bones. The cuboid bone is anterior to the calcaneus.

The five metatarsal bones form the anterior foot. The base of these bones articulate with the cuboid or cuneiform bones. The metatarsal heads, at their distal ends, articulate with the proximal phalanges of the toes. The big toe (toe number 1) has proximal and distal phalanx bones. The remaining toes have proximal, middle, and distal phalanges.

8.5 Development of the Appendicular Skeleton

The bones of the appendicular skeleton arise from embryonic mesenchyme. Limb buds appear at the end of the fourth week. The apical ectodermal ridge, located at the end of the limb bud, stimulates growth and elongation of the limb. During the sixth week, the distal end of the limb bud becomes paddle-shaped, and selective cell death separates the developing fingers and toes. At the same time, mesenchyme within the limb bud begins to differentiate into hyaline cartilage, forming models for future bones. During the seventh week, the upper limbs rotate laterally and the lower limbs rotate medially, bringing the limbs into their final positions.

Endochondral ossification, the process that converts the hyaline cartilage model into bone, begins in most appendicular bones by the twelfth fetal week. This begins as a primary ossification center in the diaphysis, followed by the later appearance of one or more secondary ossifications centers in the regions of the epiphyses. Each secondary ossification center is separated from the primary ossification center by an epiphyseal plate. Continued growth of the epiphyseal plate cartilage provides for bone lengthening. Disappearance of the epiphyseal plate is followed by fusion of the bony components to form a single, adult bone.

The clavicle develops via intramembranous ossification, in which mesenchyme is converted directly into bone tissue. Ossification within the clavicle begins during the fifth week of development and continues until 25 years of age.

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