Table of contents · 7 sections
The bones of the skull are one of the first and most challenging topics in the normal anatomy course. Exams test not only the names of the bones, but also the foramina, sulci, and the structures passing through them. This article provides a comprehensive breakdown of the neurocranium and viscerocranium, complete with foramen tables and mnemonic devices for memorization.
General skull structure
The skull (cranium) is divided into two parts:
- Neurocranium — 8 bones forming the cavity for the brain
- Viscerocranium — 15 bones forming the facial skeleton
The neurocranium consists of the calvaria and the cranial base (basis cranii). The base is divided into three cranial fossae: anterior, middle, and posterior.
Bones of the neurocranium
| Bone | Quantity | Location | Key structures |
|---|---|---|---|
| Frontal bone (os frontale) | 1 | Anterior part of the calvaria and anterior cranial fossa | Frontal sinus, supraorbital notch/foramen, orbital part |
| Parietal bone (os parietale) | 2 | Lateral parts of the calvaria | Parietal eminence, superior and inferior temporal lines |
| Occipital bone (os occipitale) | 1 | Posterior part of the calvaria and posterior cranial fossa | Foramen magnum, occipital condyles, external occipital protuberance |
| Temporal bone (os temporale) | 2 | Lateral parts of the calvaria and middle cranial fossa | Petrous part, mastoid process, styloid process, internal acoustic meatus |
| Sphenoid bone (os sphenoidale) | 1 | Middle cranial fossa, central position | Sella turcica, greater and lesser wings, pterygoid processes |
| Ethmoid bone (os ethmoidale) | 1 | Anterior cranial fossa, nasal cavity | Cribriform plate (lamina cribrosa), crista galli, ethmoidal labyrinth |
Bones of the viscerocranium
15 bones (6 paired + 3 unpaired):
- Paired: maxilla, palatine bone, zygomatic bone, nasal bone, lacrimal bone, inferior nasal concha
- Unpaired: mandible (mandibula), vomer, hyoid bone (os hyoideum)
Maxilla — the largest bone of the viscerocranium. Contains the maxillary sinus (sinus maxillaris). Participates in forming the floor of the orbit, the walls of the nasal cavity, and the hard palate.
Mandible (mandibula) — the only movable bone of the skull. Consists of a body and two rami. The ramus bears the condylar process (participating in the temporomandibular joint) and the coronoid process.
Foramina of the cranial base and passing structures
This is a core examination topic. Table of cranial fossae:
Anterior cranial fossa
| Foramen | Bone | Passing structures |
|---|---|---|
| Cribriform foramina | Ethmoid | Olfactory nerves (CN I) |
| Foramen caecum | Frontal/ethmoid | Emissary vein (inconstant) |
Middle cranial fossa
| Foramen | Bone | Passing structures |
|---|---|---|
| Optic canal (canalis opticus) | Sphenoid (lesser wing) | Optic nerve (II), ophthalmic artery |
| Superior orbital fissure | Sphenoid | CN III, IV, VI, ophthalmic nerve (V₁), superior ophthalmic vein |
| Foramen rotundum | Sphenoid | Maxillary nerve (V₂) |
| Foramen ovale | Sphenoid | Mandibular nerve (V₃) |
| Spinosum foramen (f. spinosum) | Sphenoid | Middle meningeal artery |
| Lacerum foramen (f. lacerum) | Between temporal and sphenoid | Internal carotid artery (passes above) |
Posterior cranial fossa
| Foramen | Bone | Passing structures |
|---|---|---|
| Internal acoustic meatus | Temporal (pyramid) | VII (facial) and VIII (vestibulocochlear) cranial nerves |
| Jugular foramen (f. jugulare) | Temporal/occipital | IX, X, XI cranial nerves, internal jugular vein |
| Hypoglossal canal | Occipital | XII (hypoglossal) cranial nerve |
| Foramen magnum | Occipital | Medulla oblongata, vertebral arteries, accessory nerves (XI) |
Cranial sutures
Main sutures of the cranial vault:
- Sagittal suture — between the two parietal bones
- Coronal suture — between the frontal and parietal bones
- Lambdoid suture — between the parietal bones and the occipital bone
- Squamous suture — between the parietal and temporal bones
Clinical significance: the intersection point of the sagittal and coronal sutures is bregma (anterior fontanelle in newborns). The intersection of the sagittal and lambdoid is lambda (posterior fontanelle). The pterion area (junction of the frontal, parietal, temporal, and sphenoid bones) is the thinnest part of the cranial vault. A blow to this area can lead to rupture of the middle meningeal artery and epidural hematoma.
Mnemonics for memorization
- Neurocranium bones: Frontal, 2 Parietal, Ethmoid, 2 Temporal, Occipital, Sphenoid
- Middle cranial fossa — order of foramina (medial→lateral): optic canal → superior orbital fissure → foramen rotundum → foramen ovale → foramen spinosum
- Jugular foramen: 9, 10, 11 go to the fir tree (jugulare = jugular → fir tree) — IX, X, XI cranial nerves
Frequently asked questions
How many bones are in the human skull?
23 bones: 8 — neurocranium, 15 — viscerocranium. The hyoid bone is often considered separately, yielding 22 skull bones + hyoid bone.
Which foramen is the most dangerous in trauma?
Pterion is the thinnest part of the cranial vault, beneath which runs the middle meningeal artery. A fracture in this area leads to an epidural hematoma, which can be fatal within a few hours without surgery.
Why study the foramina of the cranial base?
It is the key to neuroanatomy: knowing which nerve passes through which foramen allows you to determine the level of the lesion based on clinical symptoms. For example, superior orbital fissure syndrome (involvement of III, IV, VI, V₁) indicates pathology in the sphenoid bone area.
Study osteology through interactive anatomy lessons on the platform. See also: muscles of the upper limb, triangles of the neck and 12 pairs of cranial nerves.