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Chapter 7 The Skeleton Part C Shilla Chakrabarty, Ph.D.
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Appendicular Skeleton
Comprised of bones of the limbs and their girdles Pectoral girdle consists of clavicle and scapula, and attaches upper limbs to body trunk Very light and designed to provide great mobility to upper limbs Only clavicle attaches to axial skeleton; scapula moves freely across thorax, allowing arm to move with it Socket of pectoral girdle is shallow and poorly reinforced, allowing free movement of humerus Pelvic girdle, formed by a pair of hip bones, is sturdy and secures the lower limbs
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Pectoral Girdle (Shoulder Girdle)
Formed by clavicles anteriorly and scapulae posteriorly Medial end of each clavicle joins sternum anteriorly Distal end of each clavicle meets scapula laterally Medial borders of scapulae do not join each other or the axial skeleton Scapulae attached to thorax and vertebral column only by muscles Functions: Attach upper limbs to axial skeleton Provide attachment sites for muscles that move upper limbs Clavicle Acromio- clavicular joint Scapula (a) Articulated pectoral girdle
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Clavicles (Collarbones)
Slender, doubly curved bones, extend horizontally across superior thorax Medial two thirds convex anteriorly; lateral third concave anteriorly Flattened acromial (lateral) end articulates with scapula Cone-shaped sternal (medial) end articulates with the sternum Superior surface smooth; inferior surface ridged and grooved for attachment of ligaments and muscles Act as braces to hold scapulae and arms out laterally Transmit compression forces from upper limbs to axial skeleton Exceptionally sensitive to muscle pull Not very strong and easy to fracture NOTE: Fracture is usually anterior (outward), thus protecting the subclavian artery that serves the upper limb Acromial (lateral) end (b) Right clavicle, superior view Posterior Sternal (medial) Anterior
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Scapulae (Shoulder Blades)
Acromion Coracoid process Suprascapular notch Superior border Superior angle Subscapular fossa Medial border Inferior angle Glenoid cavity Lateral border (a) Right scapula, anterior aspect Situated on dorsal surface of rib cage, between ribs 2 and 7 Thin, triangular, flat bones with three borders and three angles Superior border: shortest, sharpest Medial border: parallels vertebral column Lateral border: thick, abuts the armpit and ends superiorly in a small, shallow fossa, the glenoid cavity Inferior angle moves extensively as arm is raised or lowered Anterior surface concave, posterior surface bears a prominent spine Spine ends laterally in large, roughened triangular projection, the acromion Acromion articulates with acromial end of clavicle to form acromioclavicular joint Coracoid process projects anteriorly from superior scapular border anchors biceps muscles bounded by suprascapular notch medially and glenoid cavity laterally Several large fossae, named according to location, house muscles Superior angle Medial border Coracoid process Suprascapular notch Acromion Glenoid cavity at lateral Lateral border Infraspinous fossa Spine (b) Right scapula, posterior aspect Supraspinous
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(c) Right scapula, lateral aspect Inferior angle
Supraspinous fossa Supraglenoid tubercle Acromion Coracoid process Glenoid cavity Spine Supraspinous fossa Infraspinous fossa Infraglenoid tubercle Infraspinous fossa Subscapular fossa Subscapular fossa Posterior Anterior (c) Right scapula, lateral aspect Inferior angle Figure 7.25c
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The Upper Limb 30 bones form skeletal framework of each upper limb
Arm : Humerus Forearm: Radius and ulna Hand: 8 carpal bones in the wrist 5 metacarpal bones in the palm 14 phalanges in the fingers
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Humerus Largest, longest bone of upper limb Articulates superiorly with glenoid cavity of scapula Articulates inferiorly with radius and ulna
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Humerus Largest, longest bone of upper limb
Articulates superiorly with glenoid cavity of scapula, and inferiorly with radius and ulna Smooth, hemispheric head fits into glenoid cavity of scapula, allowing arm to hang freely on the side Slight constriction immediately inferior to head is the anatomical neck Lateral greater tubercle and medial lesser tubercle, separated by inter-tubercular sulcus are sites of attachment for rotator cuff muscles Inter-tubercular sulcus guides tendon of biceps muscle to its attachment point at rim of glenoid cavity Surgical neck distal to tubercles is most frequently fractured part of humerus V-shaped deltoid tuberosity in middle of shaft is attachment site for deltoid muscle of shoulder Distal end has two condyles : medial trochlea (for articulation with ulna) and lateral capitulum (for articulation with radius) The condyle pair is flanked by epicondyles to which muscles attach Ulnar nerve runs behind medial epicondyle and causes painful, tingling sensation when funny bone is hit Anterior coronoid fossa and posterior olecranon fossa allow corresponding process of ulna to move freely when elbow is flexed and extended. Small radial fossa, lateral to coronoid fossa, receives head of radius when elbow is flexed Greater tubercle Lesser Inter- tubercular sulcus Lateral supracondylar ridge Radial fossa Capitulum Head of humerus Anatomical neck Deltoid tuberosity Coronoid Medial epicondyle Trochlea (a) Anterior view
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Bones of Forearm (Antebrachium)
Proximal ends of radius and ulna articulate with humerus; distal ends form joints with bones of the wrist Radius (lateral) and ulna (medial) articulate with each other proximally and distally at radio-ulnar joints Radius and ulna connected along their entire length by flat flexible ligament, the interosseus membrane Ulna Medial bone in forearm, slightly longer than radius Cup-shaped proximal end bears the olecranon (elbow) and coronoid processes, separated by the trochanter notch Forms the major portion of the elbow joint with humerus Distally, ulnar shaft narrows and ends in a knob-like head Medial to head is a styloid process from which a ligament runs to the wrist Ulnar head separated from bones of wrist by a disc of fibrocartilage which plays little or no role in hand movement Radius Lateral bone in forearm, thin at proximal end and wide distally Head (flat and shaped like a nail head) articulates with capitulum of humerus and with radial notch of ulna Rough radial tuberosity inferior to head anchors biceps muscle of the arm Medial ulnar notch articulates with ulna; lateral styloid process anchors ligaments that run to the wrist. Interosseous membrane connects the radius and ulna along their entire length Major forearm bone contributing to wrist joint Radial notch of the ulna Olecranon process Trochlear notch Coronoid Proximal radioulnar joint Distal radioulnar Styloid process of radius Radius Neck of radius Head of Ulnar notch of the radius Head of ulna Styloid process of ulna Interosseous membrane Ulna Head Neck tuberosity (a) Anterior view (b) Posterior view
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(c) Proximal portion of ulna,
lateral view Olecranon process Trochlear notch Coronoid process Radial notch View (d) Distal ends of the radius and ulna at the wrist Ulnar notch of radius Head of ulna Styloid process Articulation for scaphoid for lunate Coronoid fossa Radius Radial tuberosity Head of radius Capitulum Trochlea (c) Anterior view at the elbow region Humerus Medial epicondyle process of ulna Ulna Radial notch Olecranon process (d) Posterior view of extended elbow Lateral Head Neck
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Hand: Carpus Consists of eight bones in two rows closely united by ligaments Proximal row Scaphoid, lunate, triquetrum, and pisiform proximally Distal row Trapezium, trapezoid, capitate, and hamate distally Only scaphoid and lunate articulate with radius to form wrist joint Overuse and inflammation of tendons in this region causes carpal tunnel syndrome
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Hand: Metacarpus and Phalanges
Five metacarpal bones (#1 to #5) form the palm Phalanges Each finger (digit), except the thumb, has three phalanges—distal, middle, and proximal Fingers are numbered 1–5, beginning with the thumb (pollex) Bases of metacarpals articulate with carpals proximally; bulbous heads articulate with proximal phalanges of fingers Thumb has no middle phalanx
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(a) Anterior view of left hand (b) Posterior view of left hand
Phalanges • Distal • Middle • Proximal Metacarpals • Head • Shaft Sesamoid bones • Base Carpals Carpals Carpals • Trapezium • Hamate • Trapezium • Trapezoid • Capitate • Trapezoid • Scaphoid • Pisiform • Scaphoid • Triquetrum Radius • Lunate Ulna Radius (a) Anterior view of left hand (b) Posterior view of left hand Figure 7.28a-b
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Pelvic (Hip) Girdle Two hip bones (each also called coxal bone or os coxae) Attach lower limbs to axial skeleton with strong ligaments Transmit weight of upper body to lower limbs Support visceral organs of pelvis Secured to axial skeleton by very strong ligaments Unlike shallow glenoid cavity of scapula, sockets of pelvic girdle are deep and cuplike to firmly secure head of femur in place Lacks mobility of pectoral girdle, but is far more stable
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Pelvic (Hip) Girdle Each hip bone consists of three fused bones: ilium, ischium, and pubis Together with the sacrum and the coccyx, these bones form the bony pelvis Deep hemispherical socket on lateral surface of pelvis is acetabulum, and receives head of femur at hip joint Coxal bone (os coxae or hip bone) llium Sacroiliac joint Iliac fossa Pubic Ischium Sacrum Base of sacrum Sacral promontory Pelvic brim Acetabulum Pubic crest Pubic symphysis Iliac crest Coccyx Pubic arch Anterior inferior iliac spine Anterior superior Pubic tubercle
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Hip Bone Three regions Ilium Superior region of the coxal bone
Auricular surface articulates with the sacrum (sacroiliac joint) Ischium Posteroinferior part of hip bone Pubis Anterior portion of hip bone Midline pubic symphysis joint Ilium Ala Anterior gluteal line Posterior gluteal line superior iIiac spine Greater sciatic notch Posterior inferior iliac spine Ischial body Ischial spine Lesser sciatic Ischial tuberosity Ischium Ischial ramus Obturator foramen Inferior Acetabulum Pubic body Iliac crest Anterior Anterior inferior Pubis Inferior ramus of pubis (a) Lateral view, right hip bone
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Comparison of Male and Female Pelves
Female pelvis Adapted for childbearing True pelvis (inferior to pelvic brim) defines birth canal Cavity of the true pelvis is broad, shallow, and has greater capacity Male pelvis Tilted less forward Adapted for support of male’s heavier build and stronger muscles Cavity of true pelvis is narrow and deep
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Comparison of Male and Female Pelves
Characteristic Female Male Bone thickness Lighter, thinner, and smoother Heavier, thicker, and more prominent markings Pubic arch/angle 80˚– 90˚ 50˚– 60˚ Acetabula Small; farther apart Large; closer together Sacrum Wider, shorter; sacral curvature is accentuated Narrow, longer; sacral promontory more ventral Coccyx More movable; straighter Less movable; curves ventrally
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Table 7.4
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Table 7.4
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Table 7.4
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Carries the weight of the body Subjected to exceptional forces
The Lower Limb Carries the weight of the body Subjected to exceptional forces Three segments of the lower limb Thigh: femur Leg: tibia and fibula Foot: 7 tarsal bones in the ankle, 5 metatarsal bones in the metatarsus, and 14 phalanges in the toes
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Femur: Longest And Strongest Bone In The Body
Articulates proximally with acetabulum, and posteriorly with tibia and patella Neck Fovea capitis Greater trochanter Inter- trochanteric crest Head Intertrochanteric line Lesser trochanter Gluteal tuberosity Linea aspera Lateral condyle epicondyle Intercondylar fossa Medial and lateral supra- condylar lines Medial condyle Medial Adductor tubercle Anterior view Posterior view (b) Femur (thigh bone) Lateral epicondyle Patellar surface Posterior Facet for medial of femur Facet for lateral condyle of femur Surface for patellar ligament Apex Anterior (a) Patella (kneecap)
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Bones of the Leg Tibia Medial leg bone
Receives the weight of the body from the femur and transmits it to the foot Fibula Not weight bearing; no articulation with femur Site of muscle attachment Connected to tibia by interosseous membrane Articulates with tibia via proximal and distal tibiofibular joints Medial condyle Articular surface Tibial tuberosity Interosseous membrane Anterior border Tibia Medial malleolus Intercondylar eminence Proximal tibiofibular joint Distal tibiofibular Lateral malleolus Lateral condyle Fibula Head (a) Anterior view
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Bones of the Leg Medial condyle Articular surface of lateral condyle
of medial condyle Interosseous membrane Tibia Fibula Head of fibula Medial malleolus Lateral malleolus (b) Posterior view
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Foot Tarsals Seven tarsal bones form the posterior half of the foot
Talus transfers most of the weight from the tibia to the calcaneus Other tarsal bones: cuboid, navicular, and the medial, intermediate, and lateral cuneiforms Metatarsals Five metatarsal bones (#1 to #5) Enlarged head of metatarsal 1 forms the “ball of the foot” Phalanges The 14 bones of the toes Each digit (except the hallux) has three phalanges Hallux has no middle phalanx Medial cuneiform Phalanges Metatarsals Tarsals Navicular Intermediate Talus Calcaneus (a) Superior view Cuboid Lateral Proximal 5 4 3 2 1 Middle Distal Trochlea of talus
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Foot Talus Facet for medial malleolus Navicular Intermediate cuneiform
Sustentac- ulum tali (talar shelf) First metatarsal Calcaneus Medial cuneiform Calcaneal tuberosity (b) Medial view
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Arches of the Foot Arches are maintained by interlocking foot bones, ligaments, and tendons Arches allow the foot to bear weight Three arches Lateral longitudinal Medial longitudinal Transverse
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Arches of the Foot Arches are maintained by interlocking foot bones, ligaments, and tendons Arches allow the foot to bear weight Three arches Lateral longitudinal Medial longitudinal Transverse Medial longitudinal arch Transverse arch Lateral longitudinal arch (a) Lateral aspect of right foot
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Developmental Aspects: Fetal Skull
Infant skull has more bones than the adult skull Skull bones such as the mandible and frontal bones are unfused At birth, skull bones are connected by fontanelles Fontanelles: Unossified remnants of fibrous membranes between fetal skull bones Four fontanelles : Anterior, posterior, mastoid, and sphenoid
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Frontal suture Frontal bone Anterior fontanelle Ossification center
Parietal bone Posterior fontanelle Occipital bone (a) Superior view Parietal bone Frontal bone Ossification center Sphenoidal fontanelle Posterior fontanelle Temporal bone (squamous portion) Mastoid fontanelle Occipital bone (b) Lateral view Figure 7.35
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Developmental Aspects: Growth Rates
At birth, the cranium is huge relative to the face At 9 months of age, cranium is ½ adult size Mandible and maxilla are foreshortened but lengthen with age The arms and legs grow at a faster rate than the head and trunk, leading to adult proportions
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Developmental Aspects: Spinal Curvature
Thoracic and sacral curvatures are obvious at birth These primary curvatures give the spine a C shape Convex posteriorly
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Developmental Aspects: Spinal Curvature
Secondary curvatures Cervical and lumbar—convex anteriorly Appear as child develops (e.g., lifts head, learns to walk)
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Developmental Aspects: Old Age
Intervertebral discs become thin, less hydrated, and less elastic Risk of disc herniation increases Loss of stature by several centimeters is common by age 55 Costal cartilages ossify, causing the thorax to become rigid All bones lose mass
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