Anatomy of the Skull and
Sinuses
Last Updated: August 18, 2020
access_time15 min
Learning Objectives (4)
After completing this brick, you will be able to:
● List and describe the bones of the skull.
● 1
● List and describe the bones of the neurocranium, orbit, and nose.
● 2
● Describe the fossae and foramina of the skull and list the structures
that pass through each.
● 3
● Describe the anatomy and function of the sinuses.
● 4
CASE CONNECTION
A 25-year-old man, JD, is brought in by ambulance with multiple
injuries. He was an unrestrained rear-seat passenger in a taxi and
struck his face and head during a crash. After initial stabilization, he is
admitted to the ICU. After performing an admission assessment, the
nurse calls your attention to clear fluid coming from his nose.
,What bony injuries may be related to the clear fluid? Consider your
answer as you read, and we’ll revisit at the end of the brick.
What Are the Bones of the Skull?
The 22 bones that make up the human skull can be divided into two
groups:
● The eight bones that make up the neurocranium, which houses
the brain
● The 14 facial bones, including the mandible, which make up the
structure of the face
Grouping the 22 bones this way makes it easier to commit them to
memory. It doesn’t hurt that many of them are paired, too! Let’s look
at these groups in detail, starting with the eight bones that make up
the neurocranium.
What Bones Make Up the
Neurocranium?
Moving from the face to the back of the skull, the eight cranial bones
that make up the neurocranium are as follows: the ethmoid bone, the
sphenoid bone, the frontal bone, two parietal bones, two temporal
bones, and an occipital bone (Figure 1).
,QUIZ
Figure 1
CREDIT: ©ScholarRx
The lines where these bones meet form the major suture lines, which
fuse throughout development to form the solid cranium (Figure 2).
This fusion process is called ossification.
QUIZ
Figure 2
CREDIT: ©ScholarRx
The first major suture line is the coronal suture, which as the name
implies, runs in a coronal plane (ie, divides front from back) of the
skull. It is the joint between the frontal and parietal bones.
, Likewise, the suture that runs in the sagittal plane (ie, divides left and
right) is called the sagittal suture and is the joint where the two
parietal bones meet. The final two major suture lines are the
squamous sutures and the lambdoidal suture. The squamous sutures
are the joints between the parietal bones and the temporal bones on
the left and right. The lambdoidal suture is the joint between the
parietal bones and the occipital bone. It is named such because the
junction of those three bones forms the shape of the Greek letter
lambda (λ).
CLINICAL CORRELATION
The anterior fontanelle is the region on a child’s skull where the
frontal and two parietal plates all meet but have not fused yet. The
suture lines are open during birth to allow the neonate’s skull to
conform to the vaginal canal during delivery.
What Are the Fossae of the Skull?
A fossa is a shallow depression. There are a number of important
depressions (fossae) found around the skull. They’re important
because they are often the insertion points for muscles that help
chewing and other facial functions. Let’s start with the temporal fossa
Sinuses
Last Updated: August 18, 2020
access_time15 min
Learning Objectives (4)
After completing this brick, you will be able to:
● List and describe the bones of the skull.
● 1
● List and describe the bones of the neurocranium, orbit, and nose.
● 2
● Describe the fossae and foramina of the skull and list the structures
that pass through each.
● 3
● Describe the anatomy and function of the sinuses.
● 4
CASE CONNECTION
A 25-year-old man, JD, is brought in by ambulance with multiple
injuries. He was an unrestrained rear-seat passenger in a taxi and
struck his face and head during a crash. After initial stabilization, he is
admitted to the ICU. After performing an admission assessment, the
nurse calls your attention to clear fluid coming from his nose.
,What bony injuries may be related to the clear fluid? Consider your
answer as you read, and we’ll revisit at the end of the brick.
What Are the Bones of the Skull?
The 22 bones that make up the human skull can be divided into two
groups:
● The eight bones that make up the neurocranium, which houses
the brain
● The 14 facial bones, including the mandible, which make up the
structure of the face
Grouping the 22 bones this way makes it easier to commit them to
memory. It doesn’t hurt that many of them are paired, too! Let’s look
at these groups in detail, starting with the eight bones that make up
the neurocranium.
What Bones Make Up the
Neurocranium?
Moving from the face to the back of the skull, the eight cranial bones
that make up the neurocranium are as follows: the ethmoid bone, the
sphenoid bone, the frontal bone, two parietal bones, two temporal
bones, and an occipital bone (Figure 1).
,QUIZ
Figure 1
CREDIT: ©ScholarRx
The lines where these bones meet form the major suture lines, which
fuse throughout development to form the solid cranium (Figure 2).
This fusion process is called ossification.
QUIZ
Figure 2
CREDIT: ©ScholarRx
The first major suture line is the coronal suture, which as the name
implies, runs in a coronal plane (ie, divides front from back) of the
skull. It is the joint between the frontal and parietal bones.
, Likewise, the suture that runs in the sagittal plane (ie, divides left and
right) is called the sagittal suture and is the joint where the two
parietal bones meet. The final two major suture lines are the
squamous sutures and the lambdoidal suture. The squamous sutures
are the joints between the parietal bones and the temporal bones on
the left and right. The lambdoidal suture is the joint between the
parietal bones and the occipital bone. It is named such because the
junction of those three bones forms the shape of the Greek letter
lambda (λ).
CLINICAL CORRELATION
The anterior fontanelle is the region on a child’s skull where the
frontal and two parietal plates all meet but have not fused yet. The
suture lines are open during birth to allow the neonate’s skull to
conform to the vaginal canal during delivery.
What Are the Fossae of the Skull?
A fossa is a shallow depression. There are a number of important
depressions (fossae) found around the skull. They’re important
because they are often the insertion points for muscles that help
chewing and other facial functions. Let’s start with the temporal fossa
