Advanced Biology
Chapter 7 - Skull
Overview
• Usually consists of 22 bones
– 8 form the cranium
– 14 form the facial skeleton
• All bones but the lower jaw are interlocked by
sutures
– The lower jaw (mandible) is held to the cranium
by ligaments
Cranium
• Encloses and protects the brain
• Provides attachment points for muscles that
make chewing and head movement possible
• Some cranial bones contained air-filled cavities
called paranasal sinuses
– These sinuses are lined with mucous membranes and
are connected to the nasal cavity by passages
– Reduce the weight if the skull
– Increase the intensity of the voice by serving as
resonant sound chambers
Bones of the Cranium
Bones of the Cranium
• Frontal Bone
Bones of the Cranium
• Frontal Bone
– Forms the anterior portion of the skull above the eyes
– Includes the forehead, roof of the nasal cavity, and
roofs of the orbits (bony sockets) of the eyes
– Develops in two parts that are usually completely
fused by the fifth or sixth year of life
– Parts:
• Supraorbital foramen (or notch)
– Located on the upper margin of each orbit
– Allows nerves and blood vessels to pass to the tissues of the
forehead
• Frontal sinus
– Located above each eye near the midline
Bones of the Cranium
• Frontal Bone
Bones of the Cranium
• Parietal Bone
Bones of the Cranium
• Parietal Bones
– Located on each side of the skull just behind the
frontal bone
– Are curved and have four borders
– Sutures:
• Fused together along the sagittal suture
• Meet the frontal bone at the coronal suture
Bones of the Cranium
• Parietal Bone
Bones of the Cranium
• Occipital Bone
Bones of the Cranium
• Occipital Bone
– Forms the back of the skull and the base of the cranium
– Sutures:
• Joins the parietal bones along the lambdoid suture
– Special Features:
• Foramen magnum
– Located on the lower surface
– Allows the inferior part of the brainstem to connect with the spinal cord
• Occipital condyles
– Rounded processes
– Located on each side of the foramen magnum
– Articulate with the first vertebra (atlas) of the vertebral column
Bones of the Cranium
• Occipital Bone
Bones of the Cranium
• Temporal Bones
Bones of the Cranium
• Temporal Bones
– Form part of the sides and the base of the
cranium
– House the internal ear structures
– Sutures:
• Join the parietal bones along the squamous suture
Bones of the Cranium
• Temporal Bones
Bones of the Cranium
• Temporal Bones (cont.)
– Special Features:
• External acoustic meatus
– Located near the inferior margin
– Leads inwards to parts of the ear
• Mastoid Process
– Rounded projection
– Located below each external acoustic meatus
– Provides an attachment for certain muscles of the neck
• Styloid process
– Long, pointed process
– Located below each external acoustic meatus
– anchors muscles associated with the tongue and the pharynx
• Carotid canal
– Located near the mastoid process
– Transmits the internal carotid artery
• Jugular foramen
– Opening located between the temporal and occipital bones
– Transmits the jugular vein
• Zygomatic process
– Projects anteriorly from the temporal bone in the region of external auditory meatus
– Joins the temporal process of the zygomatic bone to form the zygomatic arch (cheek)
Bones of the Cranium
• Temporal Bones
Bones of the Cranium
• Sphenoid Bone
Bones of the Cranium
• Sphenoid Bone
– Located in anterior portion of cranium
– Consists of a central part and 2 wing-like structures
that extend laterally towards the sides of the skull
– Helps form the base of the cranium, the sides of the
skull, and the floors and sides of the orbits
– Special Features:
• Sella turcica
– Saddle-shaped depression
– Located along the midline
– Houses the pituitary gland which hangs from the base of the
brain by a stalk
• Sphenoidal sinuses
– Lie next to each other
– Separated by a bony septum that projects downward into the
nasal cavity
Bones of the Cranium
• Sphenoid Bone
Bones of the Cranium
• Ethmoid Bone
Bones of the Cranium
• Ethmoid Bone
– Located in front of the sphenoid bone
– Consists of two masses (one on each side of the nasal
cavity) joined horizontally by cribriform plates (which
form part of the roof of the nasal cavity)
• Each cribriform plate has tiny openings called olfactory
foramina through which nerves associated with the sense of
smell pass
• A perpendicular plate projects downward in the midline
from the cribriform plates to form most of the nasal septum
– Also forms sections of the cranial floor, orbital walls,
and nasal cavity walls
Bones of the Cranium
• Ethmoid Bone (cont.)
– Special features
• Superior nasal concha and middle nasal concha
– Delicate, scroll-shaped plates
– Project inward from lateral portions the ethmoid bone towards the
perpendicular plate
– Support mucous membranes that line nasal cavity
» Mucous membranes moisten, warm, and filter air as it enters the
respiratory tract
• Ethmoidal sinuses
– Small air spaces
• Crista galli
– A triangular process
– Projects upward into the cranial cavity between the cribriform plates
– Place of attachment for membranes that enclose the brain
Bones of the Cranium
• Ethmoid Bone
Facial Skeleton
• Consists of 13 immovable bones and a
movable lower jaw bone
• Form the basic shape of the face
• Provide attachments for muscles that move
the jaw and control facial expressions
Facial Skeleton
Facial Skeleton
• Maxillary Bones
• Maxillary Bones
Facial Skeleton
– Form the upper jaw
– Contain the sockets of the upper teeth
– Portions of the bones form the anterior roof of the mouth (hard
pallete) the floors of the orbits, and the sides and floor of the nasal
cavity
– All other immovable bones articulate with the maxillary bones
– Special features:
• Maxillary sinuses
– Inside the maxillae, lateral to the nasal cavity
– Largest of the sinuses (extend from the floor of the orbits to the roots of the upper
teeth)
• Palatine processes
– Portions of the maxillary bones that fuse along the midline (median palatine suture)
and form the anterior section of the hard palate
• Alveolar process
– Downward projection on the inferior border of each maxillary bone
– Together, the two processes form a horseshoe shaped arch called the alveolar arch
» Teeth occupy cavities in the arch and are bound to the bony sockets by dense
connective tissue
Facial Skeleton
• Maxillary Bones
Facial Skeleton
• Pallatine Bones
Facial Skeleton
• Palatine Bones
– L-shaped bones located behind the maxillae
– Horizontal portions form the posterior section of
the hard plate and the floor of the nasal cavity
– Perpendicular portions help form the lateral walls
of the nasal cavity
Facial Skeleton
• Pallatine Bones
Facial Skeleton
• Zygomatic Bones
Facial Skeleton
• Zygomatic Bones
– Form the prominences of the cheeks below and to
the sides of the eyes
– Help form the lateral walls and the floors of the
orbits
– Special features:
• Temporal process
– Extends posteriorly to join the zygomatic process of a
temporal bone
Bones of the Cranium
• Zygomatic Bones
Bones of the Cranium
• Lacrimal Bone
Facial Skeleton
• Lacrimal Bones
– Thin, scalelike structures located in the medial
wall of each orbit between the ethmoid bone and
the maxilla
– A groove in the anterior portion of the bone leads
from the orbit to the nasal cavity and provides a
pathway for a channel that carried tears from the
eye to the nasal cavity
Facial Skeleton
• Nasal Bones
Facial Skeleton
• Nasal Bones
– Long, thin, and nearly rectangular
– Lie side by side and are fused at the midline to
form the bridge of the nose
– Serve as attachments for the cartilaginous tissues
that form the shape of the nose
Facial Skeleton
• Vomer Bone
Facial Skeleton
• Vomer Bone
– Thin and flat
– Located along the midline within the nasal cavity
– Joins the perpendicular plate of the ethmoid bone
posteriorly to form the nasal septum
Facial Skeleton
• Inferior Nasal Concha
Facial Skeleton
• Inferior Nasal Conchae
– Fragile, scroll-shaped bones attached to the lateral
walls of the nasal cavity
– Largest of the conchae
– Located below the superior and middle nasal
conchae of the ethmoid bone
– Support mucous membranes within the nasal
cavity
Facial Skeleton
• Mandible
• Mandible
Facial Skeleton
– Horizontal, horseshoe shaped body with a flat ramus projecting at
each end
– Special Features:
• Ramus
– Divided into the mandibular condyle (posterior) and the coronoid process
(anterior)
» The mandibular condyles articulate with the mandibular fossae of the
temporal bones
» The coronoid processes provide attachments for muscles used in chewing
• Alvelolar border
– Curved bar of bone on the superior border of the mandible
– Contains the hollow sockets of the lower teeth
• Mandibular foramen
– Opening located on the medial side of the mandible, near the center of each ramus
– Admit s blood vessels and a nerve that supply the roots of the lower teeth
• Mental foramen
– Opening through which branches of the blood vessels and the nerve emerge
– Opens on the outside near the point of the jaw
– Supply the tissues of the chin and the lower lip
Facial Skeleton
• Mandible
Passageways of the Skull
• Soft spots:
Infantile Skull
– At birth, fibrous membranes connect the cranial bones
– The area where these membranes are located are called fontanels (soft
spots)
– Soft spots permit molding (some movement between the bones) which
assists in movement through the birth canal
– Closure of soft spots:
•
•
•
•
The posterior fontanel usually closes about 2 months after birth
The sphenoidal fontanel usually closes at about 3 months
The mastoid fontanel usually closes near the end of the 1st year
The anterior fontanel may not close until the middle or end of the second year
• Characteristics
–
–
–
–
–
Small face with a prominent forehead and large orbits
Jaw and nasal cavity are small
Sinuses are incompletely formed
Frontal bone is in 2 parts
Skull bones are thin and somewhat flexible and so are easily fractured
Infantile Skull