Skeletal formation
A baby’s skeleton begins as fragile membranes and cartilage, but after three months, the membranes and cartilage start turning into bone, providing protection for the internal organs, and a solid framework for the muscles.
Late in the second month of fetal development, a fetus’ skeleton is made up of thin membranes, which are about the thickness of paper tissue, and soft, flexible cartilage, like the kind you find in your ear. Over time, both types of tissue will turn into bone in a process called ossification.
Ossification occurs in two ways...the first is when membranes turn into bone.
If we look at a fetus during the third month, we can see that the membranes on the side and back of the skull are starting to ossify. That means that the bone tissue is slowly growing over the area where the membranes once existed. Eventually, these bone plates will grow together forming the cranial cavity which protects the brain.
As the baby’s development is close to birth, you can see the bones of the skull still have gaps between them. These gaps, called fontanelles, allow room for the baby’s brain to grow, and also enable the head to be compressed during delivery.
The fontanelles will remain open until the end of the second year. And even though they’re commonly known as the baby’s soft spot, the fontanelles are actually about the thickness and strength of a piece of canvas. Which kind of makes them a soft, but tough, spot.
The bones of the skull won’t stop growing until a child reaches adulthood. That’s when the joints between the bones, called the sutures, will fuse together.
Now let’s go back once again and watch the second type of ossification when cartilage turns into bone. This time we’ll look at the hand. Most of the bones of the skeleton, like the arms, legs, ribs, fingers, and backbone, start off as cartilage.
We can get a good idea of how cartilage turns into bone by looking at this portion of the hand. Here’s what it looks like on the inside.
From the second month until the end of the third month, remarkable changes take place. Watch the middle of the cartilage: both the inside and the outside turn into bone, or ossifies.
This is how the bones will continue to grow until adulthood---from the middle of the bone outward. That way they can continue to increase in their length and width.
Skeletal formation
Review Date: 11/2/2021
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
Videos
Browse All
- Abdominal aortic aneurysm
- Abdominal pain
- ACL injury
- Acne
- Adenoid removal
- Adolescent depression
- After your child's ear tube su...
- After your child's inguinal he...
- After your child's tonsil or a...
- After your child's umbilical h...
- Alcoholic liver disease
- Allergic rhinitis
- Allergies
- Allergy testing
- Allergy to mold - animal dande...
- Alzheimer disease
- Anemia
- Ankylosing spondylitis
- Anterior shoulder stretch
- Anti-reflux surgery
- Appendectomy
- Appendicitis
- Arm reach
- Arthritis
- Asperger syndrome
- Asthma
- Asthma - children
- Atopic dermatitis
- Atrial fibrillation
- Attention deficit hyperactivit...
- Autism spectrum disorders
- Basal cell carcinoma
- Before a child's tonsil or ade...
- Bipolar disorder
- Breast cancer
- Breast engorgement
- Breast self-exam
- Breastfeeding
- Bronchitis
- Bronchoscopy
- Cardiac catheterization
- Carpal tunnel syndrome
- Cataracts
- Cerebral palsy
- Cervical cancer
- Chest pain
- Childhood obesity
- Cholesterol and triglyceride t...
- Chronic obstructive pulmonary ...
- Cluster headache
- Cold treatments for kids
- Colon cancer
- Colon cancer screening
- Colorectal polyps
- Common cold
- Concussion
- Crohn disease
- C-section
- Cystic fibrosis
- Cystic fibrosis - nutritional ...
- Depression
- Diabetes
- Dialysis
- Diarrhea
- Ear infection - acute
- Ear infection - chronic
- Ear tube insertion
- Earache
- Electrocardiogram
- Endometriosis
- Enlarged adenoids
- Enlarged prostate
- Epilepsy
- Erection problems
- Essential hypertension
- External rotation with band
- Fibromyalgia
- Flu
- Food poisoning
- Foot pain
- Gallstones
- Gastroesophageal reflux diseas...
- Gastroesophageal reflux in inf...
- Getting rid of lice in the hom...
- Glaucoma
- Hardening of arteries
- HbA1c
- Head injury
- Head lice
- Healthy Guide to Fast Food
- Hearing loss
- Heart attack
- Heart failure
- Heel pain
- Hepatitis A
- Hepatitis B
- Hepatitis C
- Hernia
- Herniated disk
- Hip joint replacement
- Hodgkin lymphoma
- How do ear tubes come out?
- How to remove a splinter
- How to stop bedwetting
- How to treat a nosebleed
- How to treat a sunburn
- How to use a peak flow meter
- How to use a pill cutter
- How to use eye drops
- How to use nasal sprays
- Hypertension
- Hyperthyroidism
- Hypothyroidism
- Hysterectomy
- Infant formulas
- Inguinal hernia repair
- Inhaler with no spacer - adult...
- Inhaler with no spacer - child...
- Inhaler with spacer - adults
- Inhaler with spacer - child
- Insomnia
- Internal rotation with band
- Iron deficiency anemia
- Irritable bowel syndrome
- Isometric
- Kidney stones
- Knee joint replacement
- Let's talk about pink eye
- Lung cancer
- Lyme disease
- Melanoma
- Menopause
- Migraine
- Multiple sclerosis
- Nasal congestion
- Neck pain
- Newborn jaundice
- NICU consultants and support s...
- Nuclear stress test
- Obstructive sleep apnea
- Osteoarthritis
- Osteoporosis
- Pap smear
- Pendulum exercise
- Peptic ulcer
- Pharyngitis
- Plantar fasciitis
- Pneumonia
- Pregnancy care
- Prepare for your child's ear t...
- Prepare for your child's herni...
- Prostate cancer
- Psoriasis
- Rheumatoid arthritis
- Rotator cuff problems
- Sciatica
- Scoliosis
- Seizures
- Shingles
- Shoulder blade retraction
- Shoulder blade retraction with...
- Shoulder pain
- Sinusitis
- Sleep disorders
- Smoking tips to quit
- Spinal stenosis
- Stent
- Storing breast milk
- Strep throat
- Stretching back of your should...
- Stroke
- Systemic lupus erythematosus
- Tension headache
- The difference between a cold ...
- Tips on buying cold and flu me...
- Tips on removing ear wax
- Tonsillectomy
- Tonsillitis
- Tracking your blood pressure a...
- Treating congestion in babies...
- Treating eyelid bumps
- Type 1 diabetes
- Type 2 diabetes
- Ulcerative colitis
- Understanding cholesterol resu...
- Up the back stretch
- Urinary incontinence
- Urinary tract infection - adul...
- Uterine fibroids
- Vacation health care
- Varicose veins
- Venous insufficiency
- Wall push-up
- Wall stretch
- Warts
- What are hives?
- What are night terrors?
- What causes wheezing?
- What in the world is a neti po...
- What is tennis elbow?
- What makes your heart beat?
- What to do when kids put thing...
- What to do when kids put thing...
- What to do when something gets...
Animations
Browse All
- Allergies
- Alzheimer disease
- Ankle ligament injury
- Arrhythmias
- Atherosclerosis
- Athetosis resulting from basal...
- Balloon angioplasty - short se...
- Bladder function - neurologica...
- Blinking
- Blood clotting
- Blood flow
- Blood pressure
- Bone fracture repair
- Brain components
- Breast lift
- Breathing
- Bunion
- Cancer of the throat or larynx...
- Cardiac conduction system
- Cardiomyopathy
- Cardiovascular system
- Cataract
- Cell division
- Cerebral aneurysm
- Cesarean section
- Components of skin
- Conception - general
- Conception - pregnancy
- Conception of identical twins...
- Concussion
- Corneal injury
- Coronary artery bypass graft (...
- Coronary artery disease
- Cosmetic surgery of the face
- Coughing
- Diabetes - retinal conditions...
- Digestion
- Directional coronary atherecto...
- Early labor
- Egg cell production
- Egg production
- Endocrine glands
- Enlarged prostate gland
- Epinephrine and exercise
- Exercise
- Feeling pain
- Fetal ear development
- Formation of twins
- Gas exchange
- Glaucoma
- Gout
- Hearing
- Hearing and the cochlea
- Heart bypass surgery
- Heart formation
- Heartbeat
- Heartburn
- Herniated nucleus pulposus (sl...
- Homeostasis
- Human face formation
- Hypertension - overview
- Immune response
- Intracytoplasmic sperm injecti...
- Kidney stones
- Kids - How big is the baby?
- Kids - How does the baby come ...
- Kids - Is it a girl or boy?
- Kids - Umbilical cord
- Kids - Where do babies come fr...
- Liposuction
- Lymph nodes
- Lymphatics and the breast
- Macular degeneration
- Muscle types
- Nerve conduction
- Nervous system formation
- Nutrient exchange
- Osteoarthritis
- Osteoporosis
- Ovulation
- Parkinson disease
- Percutaneous transluminal coro...
- Peristalsis
- Phagocytosis
- Pituitary gland
- Placenta delivery
- Placenta formation
- Preeclampsia
- Pregnancy
- Red blood cell production
- Reflex response
- Retina
- Retinal detachment
- Rupturing membranes
- Seeing
- Sexual differentiation
- Shoulder joint dislocation
- Skeletal formation
- Skeletal muscle
- Skeletal system components
- Skin conditions
- Smelling
- Smoking
- Snoring
- Sperm production
- Sperm release pathway
- Stomach ulcer
- Stomach ulcer
- Stroke
- Stroke - secondary to cardioge...
- Sun's effect on skin
- Swallowing
- Sweating
- Tachycardia
- Tasting
- The role of amniotic fluid
- Tobacco use - effects on arter...
- Twin-to-twin transfusion syndr...
- Ultrasound
- Urination
- Vaccines
- Vaginal delivery
- Vasectomy