The Appendicular Skeleton

Overview

The appendicular skeleton consists of the bones of the limbs and the supporting girdles that connect them to the axial skeleton. It plays a crucial role in movement, support, and interaction with the environment. This section covers the major bones and features of the appendicular skeleton, including anatomical differences between male and female pelvises.

Shoulder Girdle (Clavicle and Scapula)

Clavicle

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

• Articulations: The sternal end articulates with the manubrium of the sternum (medially), and the acromial end articulates with the acromion process of the scapula (laterally).

• Clinical Note: The clavicle is the most commonly fractured bone in the human body and can be easily palpated.

Scapula

• Definition: The scapula is a flat, triangular bone that articulates with the clavicle and humerus.

• Glenoid Cavity: An oval fossa on the lateral aspect that articulates with the head of the humerus to form the shoulder joint.

• Tubercles: The supraglenoid and infraglenoid tubercles serve as attachment points for the biceps and triceps brachii muscles, respectively.

• Processes: The coracoid process (anterior and inferior) and the acromion process (superior and posterior, extension of the scapular spine) are prominent features.

• Borders: Medial (vertebral), lateral (axillary), and superior borders define the triangular shape. The medial border is the longest.

• Angles: Superior and inferior angles are found at the ends of the medial border.

The Upper Appendage (Upper Arm, Forearm, Wrist, and Hand)

Upper Arm (Humerus)

• Humerus: The single bone of the upper arm.

• Proximal End: The head articulates with the glenoid cavity of the scapula (ball and socket joint). The greater and lesser tubercles are attachment points for muscles, separated by the intertubercular sulcus.

• Deltoid Tuberosity: A raised area on the shaft for deltoid muscle attachment.

• Distal End: The capitulum (lateral, articulates with radius) and trochlea (medial, articulates with ulna) are the main condyles. Medial and lateral epicondyles are palpable projections.

• Olecranon Fossa: A posterior depression accommodating the olecranon process of the ulna during extension.

Forearm (Radius and Ulna)

• Radius: The lateral bone of the forearm. The head articulates with the capitulum of the humerus, allowing rotation (pronation/supination). The radial tuberosity is an attachment for the biceps brachii. The styloid process is palpable at the wrist.

• Ulna: The medial and larger bone. The olecranon process forms the elbow's point, with the trochlear notch articulating with the humerus. The coronoid process and radial notch are additional features. The distal head and styloid process are palpable near the wrist, but the ulna does not articulate with carpal bones.

Carpus (Wrist) and Hand

• Carpal Bones: Eight small bones in two rows:

  • Proximal row (lateral to medial): scaphoid, lunate, triquetrum, pisiform

  • Distal row (lateral to medial): trapezium, trapezoid, capitate, hamate

• Metacarpals: Five bones numbered 1-5 from the thumb side.

• Phalanges: Each finger has three phalanges (proximal, middle, distal), except the thumb (pollex), which has two.

Pelvic Girdle (Pelvis)

Structure and Articulations

• Pelvis: Formed by two hip bones (os coxae) that articulate anteriorly and with the sacrum posteriorly.

• Os Coxae: Each is made of three fused bones: ilium (superior), ischium (inferior posterior), and pubis (inferior anterior).

• Pubic Symphysis: The two pubis bones join anteriorly with a fibrocartilage disk.

• Sacroiliac Joint: The ilium articulates with the sacrum posteriorly.

• Acetabulum: A large lateral depression for the femoral head (hip joint).

• Iliac Crest: The superior flared region of the ilium, with anterior superior and inferior iliac spines.

• Ischial Spine and Tuberosity: The spine is a slender posterior process; the tuberosity is the roughened area you sit on.

• Obturator Foramen: A large opening for nerves and blood vessels, covered by a membrane.

Sexual Dimorphism of the Pelvis

• Female Pelvis: Wider and shallower, with a pubic arch angle greater than 90° (adapted for childbirth).

• Male Pelvis: Narrower and deeper, with a pubic arch angle less than 90°.

Lower Appendage (Upper Leg, Lower Leg, Ankle, and Foot)

Upper Leg (Femur and Patella)

• Femur: The thigh bone, largest in the body. The head articulates with the acetabulum. The neck connects the head to the shaft. The greater and lesser trochanters are muscle attachment sites.

• Gluteal Tuberosity and Linea Aspera: Posterior ridges for muscle attachment.

• Distal End: Medial and lateral condyles articulate with the tibia. The intercondylar fossa is a posterior depression.

• Patella: A sesamoid bone (kneecap) that protects the knee and assists in leg extension.

Lower Leg (Tibia and Fibula)

• Tibia: The larger, medial bone (shinbone). Proximal medial and lateral condyles articulate with the femur. The tibial tuberosity is for quadriceps attachment. The anterior crest is palpable. The medial malleolus forms the inner ankle bump.

• Fibula: The slender, lateral bone. The head articulates with the tibia. The lateral malleolus forms the outer ankle bump.

Tarsus (Ankle) and Foot

• Tarsal Bones: Seven bones divided into hindfoot (talus and calcaneus) and midfoot (cuboid, navicular, medial/intermediate/lateral cuneiforms).

• Talus: Articulates with the tibia and fibula to form the ankle joint; transmits body weight to the calcaneus.

• Calcaneus: The heel bone, attachment for the Achilles tendon.

• Metatarsals: Five bones numbered 1-5 from the medial side.

• Phalanges: Each toe has three phalanges (proximal, middle, distal), except the big toe (hallux), which has two.

Table: Comparison of Male and Female Pelvis

Additional info: The appendicular skeleton is essential for locomotion and manipulation of the environment. Understanding the anatomical differences between male and female pelvises is crucial in fields such as obstetrics, forensic science, and anthropology.