CRANIUM: NEUROCRANIUM AND CRANIAL FOSSAE
● The cranium (skull) forms the skeletal structure of the head and consists of two main
parts: Neurocranium and Viscerocranium
○ The skull has 22 bones (skull bones are flat, facial bones are irregular)
■ Paired bones (8)
● Temporal
● Maxilla
● Zygomatic
● Parietal
● Palatine
● Nasal
● Inferior nasal concha
● Lacrimal
■ Unpaired bones (6)
● Frontal
● Ethmoid
● Sphenoid
● Vomer
● Occipital
● Mandible
Neurocranium:
● The neurocranium houses the brain, its membranous coverings (cranial meninges),
proximal parts of cranial nerves, and brain vasculature.
● Composed of 8 bones in adults:
○ 4 singular bones aligned centrally:
■ Frontal
■ Ethmoidal
■ Sphenoidal
■ Occipital
○ 2 sets of bilateral bones:
■ Temporal bones
■ Parietal bones A
● Features two primary regions:
○ Calvaria (skullcap):
■ Dome-like roof composed primarily of flat bones (frontal, parietal, and
occipital).
■ These bones form via intramembranous ossification of head
mesenchyme derived from the neural crest.
○ Cranial base (basicranium):
, ■ Primarily irregular bones (sphenoid, temporal) with substantial flat
portions.
■ Formed mainly by endochondral ossification (from cartilage, also called
chondrocranium), or by a combination of ossification processes.
● Ethmoid bone:
○ Irregularly shaped, contributing minimally to the neurocranium but primarily to the
viscerocranium.
● Although termed "flat bones," the calvarial bones are curved with convex external and
concave internal surfaces.
● Most calvarial bones are connected by fibrous, interlocking sutures.
○ During childhood, some bones (sphenoid, occipital) unite by hyaline cartilage
(synchondroses).
● The spinal cord connects to the brain through the foramen magnum, a large opening
at the cranial base.
Viscerocranium (Facial Skeleton):
● Forms the anterior portion of the cranium.
● Develops primarily from embryonic pharyngeal arch mesenchyme.
● Includes bones surrounding:
○ Mouth (jaws)
○ Nasal cavity
○ Most of the orbits (eye sockets)
● Composed of 15 irregular bones:
○ 3 singular midline bones:
■ Mandible
■ Ethmoid
■ Vomer
○ 6 bilateral pairs:
■ Maxillae
■ Inferior nasal conchae
■ Zygomatic bones
■ Palatine bones
■ Nasal bones
■ Lacrimal bones
● Maxillae:
○ Form the largest part of the upper facial skeleton (upper jaw), firmly attached to
the cranial base.
○ Provide sockets and support for maxillary teeth.
● Mandible:
○ Forms the lower jaw skeleton.
○ Movable, articulates with the cranial base at the temporomandibular joints.
○ Houses mandibular teeth.
,Pneumatized Bones:
● Certain cranial bones (frontal, temporal, sphenoid, ethmoid) contain air spaces (air
cells or sinuses).
● These spaces likely reduce bone weight.
● Volume of these air spaces increases with age.
Anatomical Position and Reference:
● The cranium is oriented so the inferior margin of the orbit and superior margin of the
external acoustic opening (external acoustic meatus) lie in the same horizontal plane.
● This orientation forms the standard anatomical reference plane known as the
orbitomeatal plane (Frankfort horizontal plane) - Aligns inferior orbital margin with
external acoustic meatus
● Normae (views):
○ Norma frontalis (anterior)
○ Norma lateralis (lateral)
○ Norma verticalis (superior)
○ Norma occipitalis (posterior)
○ Norma basalis (inferior/base)
, Norma Frontalis (Anterior View)
Frontal Bone: Squamous part forms dome-shaped anterior/superior cranial wall
Nasal Region
● Nasal cavity:
○ Formed by paired nasal bones + frontal processes of maxillae
○ Piriform (pear-shaped) aperture
○ Contains 3 conchae on lateral walls:
■ Superior, middle, and inferior nasal conchae
○ Divided by bony nasal septum
Orbital Region
● Orbit:
○ Pyramidal shape (apex posterior, base anterior)
○ Connected to cranial cavity via:
■ Superior orbital fissure
■ Inferior orbital fissure
● Boundaries:
○ Superciliary arches: upper margin of orbit 1
○ Glabella: depression between superciliary arches
○ Nasion: point below glabella
Maxillae
● Paired bones forming:
○ Upper jaw
○ Inferior orbital margin
○ Lateral nasal wall
○ Cheek via zygomatic process
V
Mandible
● U-shaped bone
● Composed of:
○ Horizontal body
○ Vertical ramus
● Alveolar process: sockets for teeth
● Articulates with cranium at temporomandibular joints
● Site of muscle attachment
● Foramina in vertical alignment: =>
○ Supraorbital foramen (frontal bone) → CN V1 (ophthalmic)
○ Infraorbital foramen (maxilla) → CN V2 (maxillary)
● The cranium (skull) forms the skeletal structure of the head and consists of two main
parts: Neurocranium and Viscerocranium
○ The skull has 22 bones (skull bones are flat, facial bones are irregular)
■ Paired bones (8)
● Temporal
● Maxilla
● Zygomatic
● Parietal
● Palatine
● Nasal
● Inferior nasal concha
● Lacrimal
■ Unpaired bones (6)
● Frontal
● Ethmoid
● Sphenoid
● Vomer
● Occipital
● Mandible
Neurocranium:
● The neurocranium houses the brain, its membranous coverings (cranial meninges),
proximal parts of cranial nerves, and brain vasculature.
● Composed of 8 bones in adults:
○ 4 singular bones aligned centrally:
■ Frontal
■ Ethmoidal
■ Sphenoidal
■ Occipital
○ 2 sets of bilateral bones:
■ Temporal bones
■ Parietal bones A
● Features two primary regions:
○ Calvaria (skullcap):
■ Dome-like roof composed primarily of flat bones (frontal, parietal, and
occipital).
■ These bones form via intramembranous ossification of head
mesenchyme derived from the neural crest.
○ Cranial base (basicranium):
, ■ Primarily irregular bones (sphenoid, temporal) with substantial flat
portions.
■ Formed mainly by endochondral ossification (from cartilage, also called
chondrocranium), or by a combination of ossification processes.
● Ethmoid bone:
○ Irregularly shaped, contributing minimally to the neurocranium but primarily to the
viscerocranium.
● Although termed "flat bones," the calvarial bones are curved with convex external and
concave internal surfaces.
● Most calvarial bones are connected by fibrous, interlocking sutures.
○ During childhood, some bones (sphenoid, occipital) unite by hyaline cartilage
(synchondroses).
● The spinal cord connects to the brain through the foramen magnum, a large opening
at the cranial base.
Viscerocranium (Facial Skeleton):
● Forms the anterior portion of the cranium.
● Develops primarily from embryonic pharyngeal arch mesenchyme.
● Includes bones surrounding:
○ Mouth (jaws)
○ Nasal cavity
○ Most of the orbits (eye sockets)
● Composed of 15 irregular bones:
○ 3 singular midline bones:
■ Mandible
■ Ethmoid
■ Vomer
○ 6 bilateral pairs:
■ Maxillae
■ Inferior nasal conchae
■ Zygomatic bones
■ Palatine bones
■ Nasal bones
■ Lacrimal bones
● Maxillae:
○ Form the largest part of the upper facial skeleton (upper jaw), firmly attached to
the cranial base.
○ Provide sockets and support for maxillary teeth.
● Mandible:
○ Forms the lower jaw skeleton.
○ Movable, articulates with the cranial base at the temporomandibular joints.
○ Houses mandibular teeth.
,Pneumatized Bones:
● Certain cranial bones (frontal, temporal, sphenoid, ethmoid) contain air spaces (air
cells or sinuses).
● These spaces likely reduce bone weight.
● Volume of these air spaces increases with age.
Anatomical Position and Reference:
● The cranium is oriented so the inferior margin of the orbit and superior margin of the
external acoustic opening (external acoustic meatus) lie in the same horizontal plane.
● This orientation forms the standard anatomical reference plane known as the
orbitomeatal plane (Frankfort horizontal plane) - Aligns inferior orbital margin with
external acoustic meatus
● Normae (views):
○ Norma frontalis (anterior)
○ Norma lateralis (lateral)
○ Norma verticalis (superior)
○ Norma occipitalis (posterior)
○ Norma basalis (inferior/base)
, Norma Frontalis (Anterior View)
Frontal Bone: Squamous part forms dome-shaped anterior/superior cranial wall
Nasal Region
● Nasal cavity:
○ Formed by paired nasal bones + frontal processes of maxillae
○ Piriform (pear-shaped) aperture
○ Contains 3 conchae on lateral walls:
■ Superior, middle, and inferior nasal conchae
○ Divided by bony nasal septum
Orbital Region
● Orbit:
○ Pyramidal shape (apex posterior, base anterior)
○ Connected to cranial cavity via:
■ Superior orbital fissure
■ Inferior orbital fissure
● Boundaries:
○ Superciliary arches: upper margin of orbit 1
○ Glabella: depression between superciliary arches
○ Nasion: point below glabella
Maxillae
● Paired bones forming:
○ Upper jaw
○ Inferior orbital margin
○ Lateral nasal wall
○ Cheek via zygomatic process
V
Mandible
● U-shaped bone
● Composed of:
○ Horizontal body
○ Vertical ramus
● Alveolar process: sockets for teeth
● Articulates with cranium at temporomandibular joints
● Site of muscle attachment
● Foramina in vertical alignment: =>
○ Supraorbital foramen (frontal bone) → CN V1 (ophthalmic)
○ Infraorbital foramen (maxilla) → CN V2 (maxillary)
