The Appendicular skeleton

The appendicular skeleton consists of

Arm + Shoulder Girdle

• Scapula

• Clavicle

• Humerus

• Radius

• Ulna

• Carpals

• Metacarpals

• Phalanges

Leg + Pelvic Girdle

• Os Coxa

• Femur

• Patella

• Tibia

• Fibula

• Tarsals

• Metatarsals

• Phalanges

Your body is your cheat sheet.

To remember what whole bones look like, think about where they are, and what they do – how they move.

Let’s start with some simple examples.

What’s This?

What’s This?Cranial or postcranial?

Axial or appendicular?

Humerus

• Where is it? Upper arm (anatomically, the arm; the lower part is the forearm)

• What does it do? It rotates at the shoulder, and it flexes at the elbow.

• You now know everything you need to know to orient and side the intact humerus.

Humerus

• The shoulder is a highly mobile joint, so logically its anatomy must permit free movement.

• The elbow’s motion is more restricted. It’s a hinge, with a limited range of motion, so its anatomy is consistent of that.

• This enables you to distinguish proximal from distal.

Terminology

• The humerus is a long bone. It has a shaft, called a diaphysis, and two ends, called epiphyses.

• The proximal end is smooth bone that’s rounded, like a ball. This is called a head.

• The distal end has rounded projections of smooth bone where the humerus articulates with other bones. These areas of articulation are called condyles.

• Projections of bone next to condyles are called epicondyles.

HUMERUS

• The head is proximal and medial.

• The condyles are distal, and the rounded one (called the capitulum) is lateral.

• The epicondyles are distal and the medial epicondyle is bigger than the lateral epicondyle.

• Now you can tell proximal from distal and medial from lateral.

humerus

• The proximal humerus has two rough projections below the head anteriorly. These are called tubercles (the greater and lesser).

• The distal humerus has depressions on the anterior and posterior surfaces. A depression on bone is called a fossa. There are two shallow ones anteriorly, and one deep one posteriorly.

Humerus

• Head is proximal and medial.

• Tubercles are proximal and anterior.

• Condyles are distal and project more anteriorly.

• The olecranon fossa is deep and posterior, and there’s only one of it.

• The coronoid and radial fossae are shallow, and there are two of them.

What are these?Cranial or postcranial?

Axial or appendicular?

RADIUS AND ULNA

• Where are they? The radius and ulna are the bones of the forearm.

• What do they do? They flex at the elbow and they pivot right below it.

• This tells you what you need to know to distinguish the radius from the ulna, and how to side them.

RADIUS and ulna

• The ulna is the medial bone of your forearm. When you bend your forearm, you’re using your ulna.

• The radius is the lateral bone of your forearm. When you pronate or supinate your forearm, you’re using your radius.

Radius and ulna

• Remember, medial and lateral refers to being toward or away from the midline in standard anatomical position.

• So when we say “the radius is lateral,” we mean that it’s on the lateral side of the forearm when the skeleton is in standard anatomical position.

Radius and ulna

• Another way to remember the position of the bones is that the radius is on the thumb side of your forearm.

• When you rotate your forearm, your thumb moves. That’s your radius rotating around your ulna. The ulna stays still, the radius moves around it.

RADIUS AND ULNA

RADIUS

• Round head proximally

• Major articulation with wrist distally (large concavity)

• Ulnar notch is medial and distal

• Distal end: concave anteriorly, small tubercles posteriorly

ULNA

• Olecranon process (hook for the elbow) proximal and concave anteriorly

• Makes minimal articulation with wrist distally (small head with styloid process)

• Radial notch is lateral and proximal

The hand

• The hand consists of carpals (the wrist), metacarpals (the palm), and phalanges (the fingers).

• We’ll skip the hand for now and talk about it in the Anthropology section.

Clavicle and scapula

Clavicle

• Where is it? Anterior part of the pectoral girdle.

• What does it do? Stabilizes shoulder joint.

• smoother superiorly than inferiorly

• thick and rounded medially

• broad and flat laterally

• anterior surface is convex medially and concave laterally. (You can feel this on yourself.)

Scapula

• Where is it? The shoulderblade.

• What does it do? Articulation between humerus and torso.

• Point of triangle is inferior

• Concave surface is anterior

• Spine is posterior and superior

• Fossa for articulation with head of humerus is lateral

What’s this?

femur

• Where is it? The thigh.

• What does it do? Mobile hip joint proximally, flexes at knee distally.

• Head and neck proximal and medial.

• Trochanters proximal and lateral/posterior.

• Condyles and epicondyles distal.

Patella

• Where is it? The kneecap.

• What does it do? Improves functionality of knee joint.

• Anatomical siding: anterior surface is rough. Superior/proximal surface is flat (you can feel this on yourself). Lateral facet is the larger.

• Siding trick: put on table with rough surface up and point away from you. It falls to the side it’s from.

Tibia

• Where is it? Large bone of the lower leg.

• What does it do? Flexes at the knee proximally and at the ankle distally.

• On the medial side of the lower leg.

• Two flat condyles proximally. The medial is longer.

• Tuberosity anteriorly.

Tibia

• The medial face of the anterior shaft is convex and lies close to the skin (you can feel it on yourself).

• The lateral face of the anterior shaft is concave (you feel muscle on yourself when you touch there).

• The distal end has an articulation for the fibula laterally and a malleolus (large bone projection) medially.

Fibula

• Where is it? Smaller bone of the lower leg.

• What does it do? Stabilizes the lower leg and ankle.

• The fibula shaft is complex, so we’ll avoid the detail on that for now.

• To side, hold it with either end up with the articular facet towards you. The facet is on the side the bone is from.

Foot

• The foot consists of tarsals (ankle), metatarsals (arch), and phalanges (toes).

• It’s complex, so we’ll talk about it in detail in the anthropology section.

Os Coxa

• The two os coxae, combined with the sacrum, make up the pelvis.

• The os coxa consists of three parts, which start out as individual bones: the ilium, the ischium, and the pubis.

• The pubis is anterior. The ilium is superior. The ischium is inferior.

Os Coxa

• On the anterior os coxa, there’s a large hole. A hole in bone is called a foramen. This particular one is called the obturator foramen.

• One more word to learn: ramus. The obturator foramen is bordered by the iliopubic and ischiopubic rami. (Rami is plural of ramus).

Os Coxa

• The ilium is large, flat, and curved. It makes up the crest of your hip.

• The ischium is smaller, thick, and very dense. Its inferior margin is marked by ischial tuberosities. You sit on them.

• The pubis is relatively gracile, and it’s anterior.

Os Coxa

• Iliac crest is superior

• Sciatic notch is posterior and inferior

• Auricular surface (articulates with sacrum) is posterior and medial

• Acetabulum (articulates with femur) is lateral and opens anteriorly.

What to remember

• Know the names of the bones.

• Know where they are, and what they do. That will enable you to side them.

• How a bone moves is the biggest help to identifying it when you’re new to osteology.

REVIEW

REVIEW

FINISNext: the axial skeleton.