Skull – Embryology · FCPS Part 1

Frotanelles

Fontanelle	Location	Typical Closure Age
Posterior	Intersection of sagittal and lambdoid sutures (back of head)	1 to 2 months (earliest: 1 month)
Anterior	Intersection of sagittal, coronal, and frontal sutures (top/soft spot)	9 to 18 months
Sphenoidal (Anterolateral)	Junction of frontal, parietal, temporal, and sphenoid bones	2 to 3 months
Mastoid (Posterolateral)	Junction of parietal, occipital, and temporal bones	6 to 18 months

Bone Classification	Bones Included	Development Type
Intramembranous	Frontal, parietal, squamous part of temporal, maxilla, palatine, zygoma, tympanic part of temporal, lacrimal, nasal, vomer	Formed directly within mesenchyme without a cartilaginous precursor
Endochondral	Body of occipital, sphenoid, ethmoid, petrous part of temporal, auditory ossicles, mandibular condyle, styloid process of temporal	Formed by replacing a cartilage model
Branchiomeric (Mixed)	Maxilla, mandible, zygoma, palatine, temporal	Mixed origin (part endochondral, part intramembranous)
Anatomical Region	• Flat bones (cranial vault): Intramembranous • Skull base: Endochondral	Regional division of cranial bone development