Appendicular Skeleton: Bones and Markings of the Upper and Lower Limbs

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Appendicular Skeleton Overview

The appendicular skeleton consists of the bones of the limbs and the girdles that attach them to the axial skeleton. It is divided into the upper extremity (shoulder and arm) and the lower extremity (hip and leg). Understanding the names, locations, and features of these bones is essential for anatomy and physiology students.

Shoulder and Arm (Upper Extremity)

Clavicle

The clavicle, or collarbone, is a slender, S-shaped bone that connects the upper limb to the trunk.

Sternal end: The medial, rounded end that articulates with the manubrium of the sternum.
Acromial end: The lateral, flattened end that articulates with the acromion of the scapula.

Scapula

The scapula, or shoulder blade, is a flat, triangular bone located on the posterior thorax.

Acromion process: Lateral extension forming the highest point of the shoulder.
Coracoid process: Anterior projection for muscle attachment.
Glenoid cavity (fossa): Shallow socket that articulates with the head of the humerus.
Superior border: Uppermost edge of the scapula.
Medial (vertebral) border: Edge closest to the vertebral column.
Lateral (axillary) border: Edge closest to the armpit.
Spine: Prominent ridge running across the posterior surface.
Superior angle: Uppermost angle of the scapula.
Inferior angle: Lowermost angle of the scapula.
Supraspinous fossa: Depression above the spine.
Infraspinous fossa: Depression below the spine.
Right vs. Left Scapula: The glenoid cavity always faces laterally; the spine is posterior.

Humerus

The humerus is the long bone of the upper arm, articulating with the scapula at the shoulder and the radius and ulna at the elbow.

Head: Rounded, proximal end that fits into the glenoid cavity.
Anatomic neck: Slight constriction immediately distal to the head.
Surgical neck: Common fracture site, below the tubercles.
Deltoid tuberosity: Roughened area for deltoid muscle attachment.
Medial epicondyle: Bony projection on the distal, medial side.
Lateral epicondyle: Bony projection on the distal, lateral side.
Olecranon fossa: Posterior depression for the olecranon of the ulna.
Coronoid fossa: Anterior depression for the coronoid process of the ulna.
Capitulum: Lateral condyle that articulates with the radius.
Trochlea: Medial condyle that articulates with the ulna.
Greater tubercle: Lateral projection for muscle attachment.
Lesser tubercle: Anterior projection for muscle attachment.
Intertubercular groove (sulcus): Groove between the tubercles for the biceps tendon.
Right vs. Left Humerus: The head faces medially; the olecranon fossa is posterior.

Ulna

The ulna is the medial bone of the forearm, forming the elbow joint with the humerus.

Head: Distal end of the ulna.
Olecranon process: Prominent, proximal projection forming the elbow tip.
Coronoid process: Anterior projection at the proximal end.
Trochlear notch: Deep notch that articulates with the trochlea of the humerus.
Styloid process: Distal, pointed projection.
Radial notch: Lateral depression for articulation with the head of the radius.

Radius

The radius is the lateral bone of the forearm, important for wrist movement.

Styloid process: Distal, lateral projection.
Head: Proximal, disc-shaped structure that articulates with the capitulum of the humerus.
Ulnar notch: Medial depression at the distal end for articulation with the ulna.

Carpals, Metacarpals, and Phalanges

Carpals: Eight small bones arranged in two rows, forming the wrist.
Metacarpals: Five bones numbered I-V from thumb (lateral) to little finger (medial).
Phalanges: Fourteen bones in the fingers; each finger has proximal, middle, and distal phalanges, except the thumb, which has only proximal and distal.

Example: The index finger has a proximal, middle, and distal phalanx; the thumb has only proximal and distal phalanges.

Hip and Leg (Lower Extremity)

Hip Bone (Os Coxae or Innominate)

The hip bone is formed by the fusion of three bones: ilium, pubis, and ischium.

Iliac crest: Superior border of the ilium.
Anterior superior iliac spine: Prominent projection on the anterior ilium.
Anterior inferior iliac spine: Below the anterior superior iliac spine.
Posterior superior iliac spine: Posterior projection of the ilium.
Posterior inferior iliac spine: Below the posterior superior iliac spine.
Greater sciatic notch: Large notch below the posterior inferior iliac spine.
Lesser sciatic notch: Smaller notch below the ischial spine.
Acetabulum: Deep socket for the head of the femur.
Superior pubic ramus: Upper branch of the pubis.
Inferior pubic ramus: Lower branch of the pubis.
Symphysis pubis: Cartilaginous joint uniting the left and right pubic bones.
Ischial spine: Pointed projection from the ischium.
Ischial tuberosity: Large, roughened area for muscle attachment and weight bearing when sitting.
Obturator foramen: Large opening formed by the ischium and pubis.
Greater (false) pelvis: Area above the pelvic brim.
Lesser (true) pelvis: Area below the pelvic brim.
Pelvic inlet: Superior opening of the true pelvis.
Pelvic outlet: Inferior opening of the true pelvis.
Right vs. Left Os Coxa: The acetabulum faces laterally; the pubic symphysis is anterior.

Femur

The femur is the longest and strongest bone in the body, forming the thigh.

Head: Spherical proximal end that fits into the acetabulum.
Fovea capitis: Small pit in the head for ligament attachment.
Neck: Constricted region just below the head.
Greater trochanter: Large, lateral projection for muscle attachment.
Lesser trochanter: Medial, posterior projection for muscle attachment.
Medial condyle: Distal, medial articular surface.
Lateral condyle: Distal, lateral articular surface.
Intertrochanteric crest: Ridge connecting the trochanters on the posterior side.
Linea aspera: Prominent longitudinal ridge on the posterior shaft.
Right vs. Left Femur: The head faces medially; the linea aspera is posterior.

Patella

The patella is a triangular sesamoid bone embedded in the tendon of the quadriceps femoris muscle, protecting the knee joint.

Tibia

The tibia is the larger, medial bone of the lower leg, bearing most of the body's weight.

Medial condyle: Proximal, medial articular surface.
Lateral condyle: Proximal, lateral articular surface.
Intercondylar eminence: Raised area between the condyles.
Tibial tuberosity: Anterior projection for patellar ligament attachment.
Medial malleolus: Distal, medial projection forming the inner ankle.
Right vs. Left Tibia: The tibial tuberosity is anterior; the medial malleolus is on the medial side.

Fibula

The fibula is the slender, lateral bone of the lower leg, important for muscle attachment but not weight bearing.

Lateral malleolus: Distal, lateral projection forming the outer ankle.
Head: Proximal end of the fibula.

Tarsals, Metatarsals, and Phalanges

Tarsals: Seven bones forming the ankle, including the calcaneus (heel bone) and talus (articulates with tibia and fibula).
Metatarsals: Five bones numbered I-V from medial (big toe) to lateral (little toe).
Phalanges: Fourteen bones in the toes; each toe has proximal, middle, and distal phalanges, except the big toe, which has only proximal and distal.

Example: The second toe has proximal, middle, and distal phalanges; the big toe has only proximal and distal phalanges.

Comparative Anatomy of the Male and Female Pelvis

The pelvis differs between males and females to accommodate childbirth in females.

Feature	Male Pelvis	Female Pelvis
Coccyx curvature and flexibility	More curved, less flexible	Less curved, more flexible
Sacral width and curvature	Narrower, more curved	Wider, less curved
Pubic arch angle	Acute (<90°)	Obtuse (>90°)
Greater sciatic notch	Narrower	Wider
Pelvic inlet and outlet	Smaller, heart-shaped	Larger, oval-shaped
Ischial spine projection	Projects more medially	Projects less medially

Example: The wider pelvic inlet and outlet in females facilitate childbirth.

Summary Table: Numbering of Metacarpals, Metatarsals, and Phalanges

Bone	Number	Numbering System
Metacarpals (hand)	5	I (thumb/lateral) to V (little finger/medial)
Metatarsals (foot)	5	I (big toe/medial) to V (little toe/lateral)
Phalanges (hand/foot)	14	Proximal, middle, distal (except thumb/big toe: only proximal and distal)

Key Terms and Definitions

Appendicular skeleton: The portion of the skeleton consisting of the limbs and girdles.
Girdle: A set of bones that attaches a limb to the axial skeleton (pectoral = shoulder, pelvic = hip).
Bone marking: A specific feature on a bone, such as a projection, depression, or opening, that serves as an attachment site or passageway.

Additional info: For practical identification, always orient the bone anatomically and look for distinguishing features such as the direction of the head, the location of notches, and the shape of articular surfaces.