Glossary
of Terms
Osteology terms:
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Cranium
The cranium of the skull comprises all of the bones of the skull except
for the mandible.
Skull
The skull refers to all of the bones that comprise the head.
Calvaria
The calvaria refers to the cranium without the facial bones attached.
Calotte
The calotte consists of the calvaria from which the base has been
removed.
Splanchocranium
The splanchocranium refers to the facial bones of the skull.
Neurocranium
The neurocranium refers only to the braincase of the skull.
Endocranial
Refers to the interior of the braincase.
Axial
Refers to the head and trunk (vertebrae, ribs and sternum) of the body.
Suture
The saw-like edge of a cranial bone that serves as joint between bones of
the skull.
Aperture
An opening or space between bones or within a bone.
Cavity
An open area or sinus within a bone or formed by two or more bones.
Condyle
A rounded enlargement or process possessing an artculating surface.
Fissure
A narrow slit or gap.
Foramen
A hole in a bone usually for the transmission of blood vessels and/or
nerves.
Fossa
A pit, depression, or concavity, on a bone, or formed from several bones.
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Process
A general term describing any marked projection or prominence.
Spinous
Descriptive of a sharp, slender process.
Tubercle
A small process or bump, an eminence.
Tuberosity
A large rounded process or eminence.
Anatomical terms:
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Mid-sagittal plane
The imaginary plane that transects the the body along the mid-point into
mirrored left and right sides.
Anterior
A relative term meaning nearer the front of the body, in a biped it also
means ventral.
Posterior
A relative term meaning nearer the back of the body, in a biped it also
means dorsal.
Inferior
The relative term meaning below or of the lower portion of the body.
Superior
The relative term meaning nearer the top or of the upper portion of the
body.
Proximal
A relative term indicating a point nearer the trunk or axial skeleton, a
point nearer the mid-sagittal plane.
Distal
A relative term indicating a point that lies farther from the trunk or away
from the mid-sagittal plane.
Medial
The relative term indicating a point lying nearer the mid-sagittal plane.
Lateral
The relative term indicating a point lying farther from the mid-sagittal
plane or the midline of the body.
Lingual
Areas nearer the tongue or oral cavity.
Labial
Areas nearer the lips or cheeks.
. Introduction: Skeletal System
The skeletal system (bones and joints), working interdependently
with the skeletal muscle system (voluntary or striated muscles),
provides basic functions that are essential to life:
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Protection: protects the brain and internal organs
Support: maintains upright posture
Blood cell formation: hematopoiesis
Mineral homeostasis
Storage: stores fat and minerals.
Leverage: A lever is a simple machine that magnifies speed
of movement or force. The levers are mainly the long bones
of the body and the axes (fulcrum) are the joints where the
bones meet.
Tissues: Bones, Cartilage, and Ligaments
A living bone consists of three layers, all honeycombed with
nerves and blood vessels: 1) the periosteum, or outside skin of the
bone; 2) the hard compact bone, supporting the weight of the body;
and 3) spongy bone (bone marrow). Spongy bone occurs at the
ends of long bones and is less dense than compact bone. The spongy bone of the femur, humerus,
and sternum contains red marrow, producing red blood cells (which carry oxygen), white blood
cells (which fight infection), or platelets (that help stop bleeding). Yellow marrow, at the center,
is used to store fats.
A specialized form of connective tissue, bone consists of both organic components (e.g.
collagen) and inorganic minerals (calcium, phosphorus, magnesium, potassium, and sodium).
The minerals calcium and phosphorus give bone its hardness, strength, and rigidity to resist
compressive forces. The collagen fibers impart flexibility. Magnesium, sodium, potassium, and
other trace elements act as "mortar" bonding the calcium and phosphorous. The bone cells
themselves are embedded in a mineralized calcium "matrix" and collagen fibers.
Bone continuously remakes itself: New bone is produced and old bone is removed. Osteoblasts,
the cells responsible for making bone, maintain the balance of calcium in the blood and bone.
When this balance is disrupted, as in osteoporosis, the removal of bone exceeds its production,
making bone thin and brittle, thus more easily fractured. The intestines, vitamin D, the kidney,
parathyroid gland, and sex and adrenal hormones also play important roles in bone/calcium
balance. In long bone, illustrated above, growth occurs at the diaphysis side (shaft) of the
epiphyseal plate, thus increasing the length of the shaft. Long bone growth stops when the
hyaline cartilage stops reproducing itself and fully converts to bone.
A joint, or articulation, is a union of two or more bones. Ligaments attach bone to
bone, stabilizing and strengthening joints and determining the range of motion.
Cartilage, a gel-like substance high in proteoglycans, provides protective cushioning.
There are three types of cartilage: 1) fibrocartilage (found in intervertebral discs), 2)
elastic cartilage (found in the external ear and epiglottis), and 3) hyaline cartilage.
Hyaline (or articular) cartilage is the most important cartilage: It serves as the
"original" skeleton in the embryo from which bones develop; it spurs growth of long
bones; and it lines and protects joints.
General Classifications of Bones
1. Long Bones -- "longer than they are wide:" clavicle, humerus,
radius, ulna, femur, tibia, fibula, metatarsals, metacarpals.
Purpose: provide support and serve as the interconnected set
of levers and linkages that allow us to create movement.
(formed from hyaline/articular cartilage)
2. Short Bones: carpals and tarsals: consist mainly spongy bone
covered with a thin layer of compact bone. Purpose: allow
movement, provide elasticity, flexibility, & shock absorption.
3. Flat Bones: ribs, sternum and scapula. Purpose: protect and
provide attachment sites for muscles.
4. Irregular Bones: skull, pelvis, and vertebrae. Purposes: support weight, dissipate loads,
protect the spinal cord, contribute to movement and provide sites for muscle attachment.
5. Sesamoid Bones: a short bone embedded within a tendon or joint capsule, i.e. patella.
Purpose: alter the angle of insertion of the muscle.
Joints
Joints are classifiied into three groups: 1) immovable (fibrous) joints, e.g. skull bones; 2)
slightly movable (cartilagenous) joints, e.g. intervertebral discs; and 3) freely movable
(synovial) joints, e.g. limb joints. Synovial joints permit the greatest degree of flexibility and
have the ends of bones covered with a connective tissue (synovial membrane) filled with joint
(synovial) fluid.
A typical synovial joint, seen at right, has four main featues:
1. joint capsule - the joint enclosure, reinforced by and strengthened with ligaments
2. synovial membrane - a continuous sheet of connective tissue lining the capsule; its cells
produce synovial fluid that lubricates the joint and prevents the two cartilage caps on the
bones from rubbing together
3. synovial fluid - produced by the synovial membrane, the fluid lubricates the joint. In the
normal joint, very little fluid (less than 5cc) exists in the cavity.
4. hyaline (articular) cartilage - where the bones actually "meet"
Human Skeleton
The average human adult skeleton consists of 206 bones, attached to the muscles by
tendons. Babies are born with 270 soft bones - about 64 more than an adult. These will
fuse together by the age of twenty or twenty-five into the 206 hard, permanent bones.
The skeleton has two main parts: the axial skeleton and the appendicular skeleton. The
axial skeleton consists of the skull, the spine, the ribs and the sternum (breastbone) and
includes 80 bones. The appendicular skeleton, consisting of 126 bones, includes two
limb girdles (the shoulders and pelvis) and their attached limb bones.
Axial Skeleton (80 bones)
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skull - consiting of 1) the cranium (which encloses and
protects the brain) and 2) the facial skeleton. The upper
teeth are embedded in the maxilla; the lower teeth, in the
mandible.
mandible (jaw) - the only freely movable bone of the skull
ribs, sternum (breastbone) - comprising the
"thorax"/thoracic cage, protecting the heart and lungs
vertebral column - the "spine"
The vertebral column (illustrated below and to the left) transmits
the body weight from the head, throax, and abdomen to the lower
extremities and encloses and protects the spinal cord. Each
vertebra has essentially the same basic components, with some variation based on
location and allowed movements.
The vertebral body and the neural arch encircle the vertebral foramen. Stacked one on
top of the other, these foramina form the vertebral canal, where the spinal cord resides.
Several structures strengthen the attachments between vertebrae: 1) anterior longitudinal
ligaments in front of vertebral bodies and discs; and 2) posterior longitudinal ligaments
behind bodies and discs; 3) the compact bone of the disc itself; 4) the interlocking hyaline
cartilage surfaces of the neural arch joints; and 5) the ligaments attaching spinous
processes to transverse processes.The intervertebral discs provide shock absorption.
The orientation of the neural arch joints determines allowable motions: 1) the cervical spine (
) to rotate, flex forward, flex sideways, and extend backward; 2) the thoracic spine ( ) to
rotate; and 3) the lumbar spine ( ) to flex forward, flex sideways, and extend backward. The
sacrum ( ) has a dual character, being part of both the vertebral column and pelvis. As such, it
transmits the upper body weight to the lower exterminites.
Appendicular skeleton (126 bones, 64 in the shoulders and upper limbs and 62 in the pelvis and
lower limbs)
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Upper Extremity - The arms (humerus - upper arm bone) are ultimately attached
to the thorax, via synovial joints, at the collarbone (clavicle) and shoulder bone
(scapula) (shoulder joint). The scapula is attached to the thoracic cage only by
muscles. The elbow joint unites the humerus with the two lower arm bones - the
ulna and radius. Three sets of joints connect the radius and ulna to the bones of
the palm (metacarpals), via the eight small wrist carpals. Further, the knuckles
(metacarpophalangeal, or MCP, joints) connect the metacarpals to the proximal
phalanx of the fingers. Each finger has 3 phalanges (proximal, middle, distal),
except the thumb which has only two.
o shoulder/ scapula
o arm and forearm, elbow
o hand
Lower Extremity - The pelvis transmits the upper body weight from the sacrum (at the
sacroiliac joint) to the legs. It begins as 3 hip bones (ilium, ischium, and pubis) which
fuse together when growth is completed. The hip joint unites the pelvis to the thigh bone
(femur); the knee joint, which includes the knee cap (patella), links the femur to the
lower leg bones - the tibia and fibula. The ankle joint links the lower leg bones to the
talus. The body weight is then transmitted to the heel (calcaneous) and to the balls of the
feet via the tarsal and metatarsal foot bones. The toes have a phalangeal structure like the
fingers.
o pelvic girdle
o thigh and leg. knee,
o foot/ankle/toe
Radiologic Anatomy
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Upper Extremity
o Shoulder
o Elbow & Forearm
o Wrist
o Hand
Spine
o Cervical & Lumbar Spine
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Lower Extremity
o Pelvis and Hip
o Knee
o Ankle
o Foot
The Axial Skeleton | Skull | Vertebrate Column | Ribs | Sternum |
The axial skeleton forms the central axis of the body. It consists of the skull, the vertebral
column, the ribs and the sternum or breastbone.
The Skull.
The skull consists of 28 different bones (including the ossicles of the ear). The bones of
the skull can be divided into two main groups: the cranium which encloses and protects
the brain and the facial bones.
Lateral View of the Skull of a Human.
The Cranium
The cranium consists of eight flat bones which are rigidly attached to each other with dentate
sutures (joints with teeth-like protrusions). They envelop and protect the brain. The frontal
bone forms the forehead and portions of the eye sockets (or orbits). The occipital bone, at the
base of the skull contains a large opening, called the foramen magnum, through which the
spinal cord passes. On each side of the opening is the occipital condyle, - two round
protuberances, - by means of which the skull articulates with the first neck (or cervical) vertebra
(the atlas). The organs of hearing are situated in the temporal bone, one on each side. The
openings leading into these organs can also be seen on each side.
The Facial Bones
The facial skeleton consists of fourteen irregular bones, which are all (with the exception of the
lower jawbone) firmly attached to the cranium by means of sutures. They include the nasal
bones, the two jawbones and the cheek bones. The lower jaw articulates with the temporal
bone part of the cheek bone, just in front of the ear. This allows for the necessary movement of
the lower jaw when food is bitten off and chewed. Both upper and lower jaws have alveolar
pockets into which teeth fit.
The teeth are embedded in sockets in the ridges of the upper and lower jaw bones. Three regions
can be distinguished in a tooth:The root which are embedded in the alveolar pocket of the jaw.
The root is firmly attached to the jaw by a surrounding layer of cement and strong connective
tissue. The neck is the area where the root(s) and crown meet. The crown projects above the
gum. It is covered with a hard, white layer of enamel. The largest part of the tooth consists of
dentine which is a harder substance than ordinary bone. The dentine surrounds the cavity which
extends from the root to the crown. Blood capillaries and nerves enter the cavity at a small
opening in the tip of the root.
There are four types of teeth:
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Incisors are chisel-like teeth with sharp cutting edges found at the front of the jaws. They
are used for biting off pieces of food.
Canines (eye teeth) are sharp, pointed, cone-shaped teeth which are slightly longer than
the other teeth. They flank the incisors and are used for biting, tearing and ripping.
Premolars are situated behind the canines. They have flat surfaces with two pointed
protuberances (cusps), which are used for chewing and grinding the food.
Molars are larger and better developed than the premolars. They are found at the back of
the mouth, behind the premolars. They have broad, flat surfaces with 3 pointed
protuberances (cusps) and are also used for chewing and grinding the food. They usually
have 2 to 3 roots.
Structure of a Tooth.
Initially a human has a temporary set, or a milk set of 20 teeth with a tooth formula 2.1.2
over 2.1.2. After shedding the temporary set humans get a permanent set of 32 teeth with
a tooth formula 2.1.2.3 over 2.1.2.3.
The Vertebral Column.
The vertebral column forms the central part of the skeleton. It supports the skull and
protects the spinal cord. It also serves as attachment for the ribs, the pectoral and
pelvic girdles. The vertebral column consists of separate bones, the vertebrae. The
different vertebrae are arranged above each other. Because the separate vertebrae are
attached to each other by means of fibrous cartilaginous discs they form a flexible
column. Each vertebra has articular surfaces above and below, which allow articulation
movement between them.
The vertebral column of 33 vertebrae is divided into five regions according to their
position and structure. The five regions consist of: Seven cervical (neck) vertebrae,
Twelve thoracic (chest) vertebrae, Five lumbar vertebrae, Five fused sacral vertebrae,
and Four fused vertebrae.
Structure of a Typical Vertebra.
A typical vertebra consists of the centrum, a neural arch, a neural spine, two
transverse processes and four articular processes with articulating surfaces. The
centrum is the front part (anterior) and consists of a solid piece of spongy bone
encircled by a layer of compact bone. The upper and lower surfaces are flat and rough
and provide attachment for the cartilaginous discs. These surfaces allow a limited
degree of movement. The posterior (back) part is called the neural arch. An opening, (
foramen) is formed between the centrum and the neural arch. The spinal cord goes
through this opening. The neural canal is formed by the vertebral foramina in the
successive vertebrae and it encloses and protects the spinal cord. The neural spine is
directed backwards. The two transverse processes project laterally and serve for the
attachment of ligaments and muscles. The neural arch has four smaller articular
processes with articular surfaces, two on the upper and two on the lower aspect of the
vertebra. These articulating surfaces are covered by hyaline cartilage. The spinal nerves
leave the vertebral column through the openings between each succeeding pair of
vertebrae.
The Vertebral Column.
The Cervical Vertebrae
The neck region consists of 7 cervical vertebrae. These are the smallest vertebrae in
the vertebral column. The first two cervical vertebrae are known as the atlas and axis.
They are specially adapted to support the skull and to enable it to move. They differ
from the structure of the typical vertebra in certain respects.
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The Atlas
The atlas is the first neck vertebra and supports the skull. It is ring-shaped and
has no centrum. A neural spine is absent. The atlas consists of posterior and
anterior neural arches and 2 short transverse processes. The spinal foramen
(neural canal) is very large. The 2 occipital condyles of the skull fit into the
articulating facets on the upper surface of the atlas, on either side of the neural
canal. On its lower surface (inferior) surface the atlas has 2 articular surfaces for
articulation with the axis.
The Atlas
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The Axis.
The axis has a large, strong neural spine. The centrum is small and has become
modified to bear the odontoid process (a tooth-like projection) on its upper
surface. The odontoid process fits against the facet in the anterior arch of the atlas.
This forms a pivot joint or axis, around which the atlas (together with the skull)
can rotate, so allowing the head to turn from side to side.
The Axis
The Thoracic Vertebrae.
There are 12 thoracic vertebrae. The centrum is large and sturdy and the neural
spines are long and directed downwards. The long neural spines form an anchorage
for the muscles and ligaments that support the head and neck. The head (or capitulum)
of each of the first 10 pairs of ribs fits into and articulates with the semi-circular facet
which is situated between two successive centra, i.e. between the inferior surface of one
and the superior surface of the next centrum. These facets occur on both sides of the
centrum. The tubercle of the rib articulates with the facet at the tip of the transverse
process.
The Lumbar Vertebrae.
These 5 vertebrae are the largest and strongest in the vertebral column. The transverse
processes are very long for the attachment of the powerful back muscle that maintain the
posture and flex the spine in movement.
The Sacrum.
The sacrum is roughly triangular in shape and consists of 5 fused vertebrae. It lies
between the hip bones, with which it articulates. Horizontal ridges indicate the divisions
between the fused vertebrae. At the ends of these ridges are openings which allow nerves
and blood vessels to pass through.
The Sacrum and Coccyx as seen from the front.
The Coccyx.
The coccyx consists of 4 fused tail vertebrae which are small and have a relatively
simple structure. They do not resemble the structure of a typical vertebra. The muscles
of the buttocks are attached to the coccyx.
The Ribs.
Twelve pairs of ribs articulate with the 12 vertebrae of the thoracic region. The ribs are
flat, narrow bones with a distinctive bow-shaped curve. Each rib consists of a head or
capitulum, a small tubercle (which is a short distance back from the head) and the shaft.
The head of the rib articulates with the semi-circular articulating facets formed by the
centra of two successive thoracic vertebrae. The tubercle fits into and articulates with the
articulating facets on the transverse process. The first seven ribs on each side are joined
to the breastbone by bars of hyaline cartilage (called costal cartilage in this region). The
first seven pairs of ribs are referred to as true ribs. The cartilages of the 8th, 9th and 10th
ribs are joined to the costal cartilage of the rib immediately above (i.e. to the costal
cartilage of the 7th rib). These three pairs of ribs are known as vertebrochondral ribs.
The last two pairs of ribs have free ends which are not attached to the sternum at all.
They are floating ribs. The vertebrochondral ribs and the floating ribs are collectively
known as false ribs. The ribs (together with their muscles) play an important role in the
breathing mechanism of a mammal.
Diagram to illustrate the attachment of the ribs to the thoracic vertebrae
and sternum.
The Sternum (Breastbone).
The sternum is a long, flat, dagger-shaped bone. It is about 15 - 18 cm long and is
found in the center of the chest region. The broad upper end supports the collar bones.
The first seven pairs of ribs are attached to the articulating facets on the sides of the
sternum. The 12 thoracic vertebrae, the 12 pair of ribs and the sternum forms the thorax
which protects the delicate and vital organs of the thorax, viz. the heart and lungs.
The Cranium: A General Overview
The Cranium, also called the "Skull," describes the skeleton of the head, face and
mandible.
It is a portion of the axial skeleton, or that portion associated with the central nervous
system. Those portions of the skeleton not associated with the central nervous system, are
associated with the appendicular skeleton or the extremities (i.e., the arms and legs).
The axial skeleton consists of the cranium, all the osseous elements of the vertebral
column, the ribs, and the sternum.
In an adult, various of the bones of the cranium are paired left and a right, while others,
which cross the mid-sagittal plane, are unpaired. Furthermore, the bones of the skull are
classified as those which are called Cranial Bones, or contribute to that portion
surrounding the brain, or Facial Bones(i.e., those which do not assist in forming the
braincase).
The Individual Bones
Each of the bones of the cranium posses a number of distinctive features which not only allow
the bone to be identified, but also permit its exact location and orientation in the body to be
determined (i.e., as a left or right, medial- lateral, posterior-anterior, inferior-superior, etc.). The
features listed as characteristic of each of the bones depicted in the Skull Module serve as an aid
in such an identification. While the list of features accompanying each bone is by no means
complete, the major ones are introduced. The elements of the inner ear (i.e., the Malleus, Incus,
and Stapes), as well as the individual teeth will be addressed.
You must know:
Paired Cranial Bones:
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Parietals
Temporals
Unpaired Cranial Bones:
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Frontal
Occipital
Sphenoid
Ethmoid
Paired Facial Bones:
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Unpaired Facial Bones:
Lacrimals
Nasals
Zygomatics
Maxillae
Palatines
Inferior Nasal Conchae
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Vomer
Mandible
Hyoid
The Parietal Bones
The Parietals are paired left and right. Externally, each possess a Superior, and Inferior
Temporal Line, to which the temporal muscle is attached. The lines run from the
Frontal Crest of the anterior frontal bone to the Supra-Mastoid Crest on the posterior
portion of the temporal bone. The parietals articulate with each other by way of the MidSagittal Suture, and with the frontal bone anteriorly by way of the Coronal Suture.
These two sutures generally form a right angle with one another. Posteriorly, the parietals
articulate with the Occipital Bone by way of the Lambdoid Suture. The intersection of
the Lambdoid and Sagittal Sutures approximate a 120 degree angle on each of the
parietals and the occipital bone. Among the sutures the Lambdoid is by far more serrated
than either the Sagittal or the Coronal. Inferiorly the Parietal articulates with the temporal
bone by way of the Squamosal and Parieto-Mastoid Sutures. On the external surface
near the center of the bone is the Parietal Eminence. Slightly posterior to the eminence
there may be a Parietal Foramen.
Internally, the bones possess a number of Meningeal Groves as well as perhaps some
number of Arachnoid Foveae. The groves generally branch from the inferior/anterior
edge of the bone to superior/posterior, while the foveae are freqquenly found along the
sagittal suture. At the area of intersection of the lambdoid and parieto-mastoid sutures
there is a brief portion of the Sigmoid (i.e., Transverse) Sulcus.
The Temporal
The Temporal Bone is another paired cranial bone which is difficult to describe due to
its various features, and projections. It consists of two major portions, the Squamous
Portion, which is flat or fan-like and projects superiorly from the other, very thick and
rugged portion, the Petrosal Portion.
The squamous portion assists in forming the Squamous Suture which separates the
temporal bone from the adjacent and partially underlaying parietal bone. The petrosal
portion contains the cavity of the middle ear and all the ear ossicles; the Malleus, Incas
and Stapes. This portion projects anterior and medialy beneath the skull. Projecting
inferiorly from the petrosal portion is the slender Styloid Process which is of variable
length. The styloid process serves as a muscle attachment for various thin muscles to the
tongue and other structures in the throat. Externaly the petrosal portion possesses the
External Auditory Meatus while internally there is an Internal Auditory Meatus.
Anterior to the external meatus the Zygomatic Process has its origin. This process
projects forward toward the face and its articulation with the temporal process of the
zygomatic. Just anterior of the external meatus and inferior of the origin of the zygomatic
process is the Glenoid or Mandibular Fossa which assists in forming the shallow socket
of the Tempro-Mandibular Joint. Posterior to the external auditory meatus is the
inferiorly projecting Mastoid Process which serves as an attachment for the
sternocleidomasotid muscle. Above the mastoid process is the Supramastoid Crest to
which the posterior portion of the temporal muscle is attached.
Unpaired Cranial Bones: Frontal Occipital Sphenoid Ethmoid
The Frontal Bone
The frontal bone may be divided into two main portions, a vertical squamous portion which
articulates with the paired parietals along the Coronal Suture and forms the forehead, and two
orbital plates, which contribute to the ceiling and lateral walls of the left and right eye orbits.
On the external surface the squamous portion frequently possesses a left and right Frontal
Eminence. Additionally, the bone possesses two Supra-Orbital Ridges (i.e., Superciliary or
Brow Ridges) which are bumps above each of the eye orbits. In early hominids these ridges
formed a Torus or large shelf-like process protruding from above the eyes. Associated with
each Superior Orbital Margin of the eye orbit the frontal bone may posses a Supra-Orbital
Notch or if completely surrounded by bone, a Supra-Orbital Foramen. Above the frontonasal suture which allows articulation between the frontal and nasal bones there is generally a
trace of the vertical Metopic Suture. In early life the metopic suture divided the frontal bone
into left and right halfs. With in the bone, and above and the metopic suture, is the Frontal
Sinus. The left and right Frontal Crest, begins at each Zygomatic Process of the frontal bone,
and provides the anterior origin of the Temporal Line to which the left and right temporal
muscle is attached.
Internally, the frontal bone possesses the Median Sagittal (i.e., Sagittal-Frontal) Crest which
separates the two frontal hemispheres of the brain.
The frontal touches, or articulates with, the following bones: Sphenoid Parietals Ethmoid
Lacrimals Nasals Zygomatics Maxillae
The Occipital Bone
The Occipital Bone consists of a large squamous, or flattened portion separated from a small
thick basal portion by the Foramen Magnum on either side of which is a left or right Occipital
Condyle. The occipital condyles articulate with the first cervical vertebrae (the Atlas).
Externally, the squamous portion of the bone possesses Superior, Middle, and Inferior Nuchal
Lines to which the muscles at the back of the neck are attached. The External Occipital
Protuberance lies on the superior nuchal line in the mid-sagittal plain. Lateral to each occipital
condyle are the Condylar Fossae and Foramen while the Hypoglossal Canal is medial to them.
Internally, are the Sagittal and Transverse Sulci, or grooves which converge at the Confluence
of Sinuses. A single internal Occipital Protuberance or Cruciform Eminence is also found in
this area. Running inferior from the eminence to the foramen magnum is the Internal Occipital
Crest which separates the Cerebellar Fossae. The transverse sulci assist in directing the
developing jugular vein to the Jugular Notch on either side of the basilar portion of the
occipital.
The occipital touches, or articulates with, the following bones: Parietals Temporals Sphenoid
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Atlas
The atlas is not part of the skull. It is the first of the seven cervical vertebrae and the one
upon which the base of the skull sits. It is the bone around which the skull rotates, hence
the name "atlas."
The Sphenoid
The Sphenoid is one of the more difficult bones to describe and invision. It has a number of
features and projections, which allow it to be seen from various views of the skull. It is a single
bone that runs thrugh the mid-sagittal plane and aids to connect the cranial skeleton to the facial
skeleton. It consists of a hollow body, which contians the Sphenoidal Sinus, and three pairs of
projections: the more superior Lesser Wings, the intermediate Greater Wings, and the most
inferior projecting Pterygoid Processes. Internally upon the body is the Sella Turcica where the
pituitary gland rests in life. The smaller lesser wings posssesses the Optic Foramen through
which the optic or second cranial nerve passes before giving rise to the eye. The Supra-Orbital
Fissure separates the lesser wing superiorly from the greater wing below and can best be viewed
on the posterior wall of each eye orbit. The left and right greater wings assist in forming the
posterior wall of each of the eye orbits where it forms an Orbital Plate. In addition the external
surface of the greater wing can be viewed in the the lateral view of the cranium in an area called
the Pterion Region. Just inferior to the supra-orbital fissure near the body of the sphenoid, each
of the greater wings also possess a Foramen Rotundum which in life transmits the maxillary
branch of the fifth, or trigeminal, cranial nerve. Each of these wings also possesses a much larger
Foramen Ovale more laterally, which transmits the the mandibular branch of the same nerve.
More posteriorly is the smallest of the three pairs of foramena, the Foramen Spinosum which
transmits the middle meningial vessels and nerve to the tissues covering the brain.
The left and right pterygoid processes project inferiorly from near the junction of each of the
greater wings with the body of the sphenoid. These processes run along the posterior portion of
the nasal passage toward the palate. Each process is formed from a Medial and Lateral
Pterygoid Plate to which the respective medial and lateral pterygoid muscle is attached during
life. The muscles run from these attachments to the internal, or medial surface, of the mandible
in the area of the gonial angle. In life the muscles assist in creating the grinding motion
associated with chewing.
The sphenoid touches, or articulates with, the following bones: Illustrate the following bones
and state the function of each.
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Vomer
Ethmoid
Frontal
Occipital
Parietals
Temporals
Zygomatics
Palatines
The Ethmoid
If the sphenoid is the most difficult cranial bone to describe and invision, the Ethmoid is the
second most difficult. It has a number of features and projections, but unlike the sphenoid it
cannot be seen from various views of the skull. Like the sphenoid, it is a single bone that runs
through the mid-sagittal plane and aids to connect the cranial skeleton to the facial skeleton. It
consists of various plates and paired projections. The most superior projection is the Crista
Galli, or Cocks Comb, found within the cranium. It assists in dividing the left and right frontal
lobes of the brain. Lateral projections from the Crista Galli are the left and right Cribriform
Plates which in life cradle the first cranial nerves i.e., the olfactory nerves. The nerves brachiate
through the porosity of these plates into the nasal cavity below. Directly inferior to the Crista
Galli and running in the mid-sagittal plane is the Perpendicular Plate of the ethmoid which
articulates with the vomer more inferiorly and assists in separating the left and right nasal
passages. The Perpendicular Plate can be viewed anteriorly through the nasal cavity.
Descending off each of the Cribriform Plates is a left or right Orbital Plate which aids to form
the medial wall of the respective eye orbit. Each Orbital Plate is rectangular in shape and gives
rise to two medial projections, the Superior and Middle Nasal Concha. These projections, like
the separate Inferior Nasal Concha, assist in increasing the surface area within the nasal cavity
and thereby the exposure of the brachiating olfactory nerve to inhaled odors. The Superor or
Supreme Nasal Conche are smaller, and cannot be viewed through the anterior nasal opening
because it is blocked from view by the the more inferior Middle Nasal Conche.
The ethmoid touches, or articulates with, the following bones: Sphenoid Frontal Maxillae
Palatines Vomer Lacrimals
Paired Facial Bones: Lacrimals Nasals Zygomatics Maxillae Palatines
Inferior Nasal Conchae
The Lacrimal Bone
The Lacrimal bones are the smallest and most fragile of the facial bones. They are paried
left and right and assist in forming the anterior portion of the medial wall of each eye
orbit. They are basicaly rectangular with two surfaces and four borders. Each of the
borders articulate with the bones that surround the Lacrimal. The Orbital or Lateral
Surface contributes to the eye orbit, while the Medial Surface assists in forming a small
portion of the nasal passage. The orbital surface possesses a sharp superior-inferior
running ridge called the Posterior Lacrimal Crest which divides this surface into an
Orbial Plate and the Lacrimal Sulcus. The sulcus, along with a contiguous sulcus on the
maxillae, assists in forming the lacrimal fossa which contains the lacrimal duct in life.
The duct connects the medial corner of the eye to the nasal passage and allows tears from
the eye to be shunted into the nasal passage.
The lacrimals touch, or articulate with, the following bones:
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Frontal
Ethmoid
Maxillae
The Nasal Bones
Each of the nasal bones is a small rectangular bone which together form the bridge of the nose
above the Nasal Cavity also called the Piriform Aperture. They articulate with each other by
way of the Internasal Suture and with the frontal bone superiorly by way of the Fronto-Nasal
Suture just below the glabellar region of the frontal bone. The intersection of these two sutures
marks the anatomical landmark called Nasion. Laterally, each of the nasal bones articulates with
the frontal process of the maxilla.
A nasal touches, or articulates, the following bones:
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Frontal
Maxilla
Nasal
The Zygomatic Bones
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Also called the Malars or Jugals, each cheek or zygomatic bone possesses three major processes
which articulate with the bones which surround it. The Frontal Process of the zygomatic forms
the lateral margin and wall of the eye orbit and projects superiorly to articulate with the
zygomatic process of the frontal bone. This portion of the bone separates the eye orbit from the
temporal fossa and possesses a posterior projecting edge called the Marginal Process. The
Temporal Process of the zygomatic runs lateral and posterior toward an articulation with the
zygomatic process of the temporal bone. Together these two processes assist in forming the
zygomatic arch which serves as the attachment for the masseter muscle in life, one of the
primary muscles used in mastication. The temporal muscle runs beneath the arch and is also a
primary mover of the mandible in chewing. The Maxillary Process of the zygomatic articulates
with the zygomatic portion of the maxilla by way of the Zygo-Maxillary Suture.
The zygomatics touch, or articulate with, the following bones:
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Frontal
Sphenoid
Maxillae
Temporals
The Maxillae
The Maxillae are the paired facial bones which contain the upper dention and thus form
the upper jaw. Each is basicly hollow with a large Maxillary Sinus. A superior
projection, the Frontal Process, assists in forming the lateral margin of the nasal aperture
and ends by articulating with the frontal bone. An Orbital Plate forms the floor of the
eye orbit, while the Zygomatic Process articuates with the zygomatic bone. On the
anteror surface of the bone, near the maxillo-zygomatic suture, ther is an Infra-Orbital
Foramen. The Alveolar Process of the Maxilla contains the upper dentition and assists
in giving rise to the Palatine Portion which forms the anterior half of the hard palate.
The left and right Maxillae articulate with one another by way of the Inter-Maxillary
Suture. The superior end of this suture frequently terminates with the Nasal Spine.
A maxilla touches, or articulates with, the following bones:
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Frontal
Ethmoid
Zygomatic
Vomer
Lacrimal
Maxilla
Nasal
Palatine
Mandible
Inferior Nasal Concha
The Palatine Bones
The Palatine Bones are paired left and right and articulate with one another in the mid-sagittal
plane at the Interpalatine Suture. Both bones assist in forming the posterior portion of the hard
palate as well as a portion of the nasal cavity. Each bone possesses a Horizontal Part, with an
inferior surface which forms the posterior portion of the hard palate and a superior surface that
assists in forming the posterior portion of the floor of the nasal cavity. The Vertical Part of each
contributes to the lateral wall of the nasal cavity. Near the posterior junction of the Vertical and
Horizontal Parts on the palatal surface is a Palatine Foramen. Each bone possesses a number of
processes and articular surfaces which touch the bones that surround it.
A palatine touches, or articulates with, the following bones:
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Sphenoid
Ethmoid
Maxilla
Vomer
Palatine
The Inferior Nasal Concha
The Inferior Nasal Concha is a very thin, porous, and fragile, paired bone basically elongated
and curled upon itself. It lays in the horizontal plane and is attached to the lateral wall of the
nasal cavity. By way of the Maxillary Process on the bone's lateral surface, it is attached to
the maxilla, and by way of the Lacrimal, Ethmoid and Palatine Processes to each of the
bones which assist in forming the lateral wall of the nasal cavity. By projecting into the nasal
cavity, the medial surface of the Inferior Nasal Concha assists in increasing the surface area
within the cavity and thus increases the amount of mucus membrane and olfactory nerve
endings exposed to inhaled odors.
An inferior nasal concha touchs, or articulates with, the following bones:
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Ethmoid
Lacrimal
Maxilla
Palatine
Unpaired Facial Bones: Vomer Mandible Hyoid
The Vomer Bone
The Vomer is a single relatively flat bone located in the mid-sagittal plane. It articulates with the
perpendicular plate of the ethmoid superiorly and together aid in forming the nasal septum.
While it is frequently deflected slightly to the left or right, in general the septum is aligned
perpendicularly and divides the the nasal aperture into the the left and right nasal passages. In
addition to the Perpendicular Portion, superiorly the Vomer mushrooms out into a pair of Alae
which terminate and articulate with the sphenoid in a heart shaped process. Inferiorly the Vomer
rests on both the maxillae and the palatines.
The vomer touches, or articulates with, the following bones:
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Sphenoid
Ethmoid
Palatines
Maxillae
The Mandible
The Mandible or lower jaw consists to four major portions, a left and right Mandibular
Ramus and the left and right Body. The Alveolar Process of the body is that portion of the
mandible which contains the lower dentition. The junction of the ramus and the body occurs at
the Gonial Angle where externally one of the masseter muscles is attatched. The left and right
masseters make up a set of two sets of muscels used in chewing. At the gonial angle on the
internal surface the Pterygoid Attachements are found. These attachements are for the medial
and lateral pterygoid muscles which assist in the grinding motion of chewing. The external
surface of the mandibular body possesses the Mental Foramen and at the midline, the Mental
Protuberance or chin. The internal surface of the body possesses the Lingual Foramen, the
Mandibular Canal, and the longitudinal running Mylo-Hyoid Ridge. The Genio Tubercle is
located in the mid-sagittal plane on the internal surface of the mandible. The superior margin
of each ramus possesses both a Mandibular Condyle or Head, for articulaltion with the
temporal bone at the tempro-mandibular joint, and the Coronoid Process, for the attachement
of the temporalis muscle (one in the set of primary muscles used in mastication). The mandible
articulates with each of the Maxillae by way of their contained respective lower and upper
dentition.
The mandible touches, or articulates with, the following bones:
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Temporals
Maxillae
The Hyoid Bone
The hyoid is a single small "U" shaped bone in the adult which does not articulate
with any other bone. It is suspended from the styloid process of each temporal bone
by means of the stylohyoid ligaments. It is located in the mid-sagittal plane, at the
front of the throat, and beneath the mandible but above the larynx near the level of the
third cervical vertebrae. It is formed from three separate parts (i.e., the Body,and the
left and right Greater and Lesser Cornu) which fuse in early adulthood. The base of
the "U" shaped bone is located anteriorly while the Cornu project posteriorly.
The hyoid does not articulate with (i.e., touch) any other bones.
The Temporomandibular Joint (TMJ)
The temporomandibular joint (TMJ) is a small joint located in front of the ear where the skull
and lower jaw meet. It permits the lower jaw (mandible) to move and function.
TMJ disorders are not uncommon and have a variety of symptoms. Patients may complain of
earaches, headaches and limited ability to open their mouth. They may also complain of clicking
or grating sounds in the joint and feel pain when opening and closing their mouth. What must be
determined, of course, is the cause.
What Causes TMJ Disorders?
Determining the cause of a TMJ problem is important, because it is the cause that guides the
treatment.
Arthritis is one cause of TMJ symptoms. It can result from an injury or from grinding the teeth at
night. Another common cause involves displacement or dislocation of the disk that is located
between the jawbone and the socket. A displaced disk may produce clicking or popping sounds,
limit jaw movement and cause pain when opening and closing the mouth.
The disk can also develop a hole or perforation, which can produce a grating sound with joint
movement. There are also conditions such as trauma or rheumatoid arthritis that can cause the
parts of the TMJ to fuse, preventing jaw movement altogether.
Anatomy of the TMJ
The TMJ is a hinge and gliding joint and is
the most constantly used joint in the
body. The round upper end of the lower
jaw, or the movable portion of the joint,
is called the condyle; the socket is called
the articular fossa. Between the condyle
and the fossa is a disk made of cartilage
that acts as a cushion to absorb stress
and allows the condyle to move easily
when the mouth opens and closes.
The Joint, the Muscles or Both are the Problem
Stress may trigger pain in the jaw muscles that is very similar to that caused by TMJ problems.
Affected patients frequently clench or grind their teeth at night causing painful spasms in the
muscles and difficulty in moving the jaw. Patients may also experience a combination of muscle
and joint problems. That is why diagnosing TMJ disorders can be complex and may require
Function of the TMJ
Temporomandibular joint — Normal closed position. Jawbone is separated from skull
by a soft disk that acts as a cushion when you chew, speak or swallow.
Temporomandibular joint — Noraml open position. Disk stays in place when jaw is in
use.
Temporomandibular joint — Abnormal. Disk is pulled forward when jaw is in use,
causing the bone structures to grind together.
different diagnostic procedures.
The Role of the Oral and Maxillofacial Surgeon
When symptoms of TMJ trouble appear, an oral and maxillofacial surgeon should be
consulted. A specialist in the areas of the mouth, teeth and jaws, the oral and
maxillofacial surgeon is in a good position to correctly diagnose the problem.
Special imaging studies of the joints may be ordered and appropriate
referral to other dental or medical specialists or a physical therapist
may be made.
Range of Possible Treatment
TMJ treatment may range from conservative dental and medical care to complex surgery.
Depending on the diagnosis, treatment may include short-term non-steroidal antiinflammatory drugs for pain and muscle relaxation, bite plate or splint therapy, and even
stress management counseling.
Generally, if non-surgical treatment is unsuccessful or if there is clear joint damage,
surgery may be indicated. Surgery can involve either arthroscopy (the method identical to
the orthopaedic procedures used to inspect and treat larger joints such as the knee) or
repair of damaged tissue by a direct surgical approach.
Once TMJ disorders are correctly diagnosed, appropriate treatment can be provided.
Treatment Options for TMJ Disorders
Bite splints or guards are commonly used to treat TMJ disorders.
Some of the TMJ surgical options your OMS may consider include (a)
Arthrocentesis — flushing fluid from the joint and gently stretching it.
(b) Arthroscopy — using a miniature telescoping instrument to
diagnose and repair the joint. (c) Arthrotomy — open joint surgery for
more complex cases.