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In
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct therapsid ...
s, cervical vertebrae (singular: vertebra) are the
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e of the
neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
, immediately below the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
. Truncal vertebrae (divided into
thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
and
lumbar vertebrae The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse ...
in
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s) lie caudal (toward the tail) of cervical vertebrae. In
sauropsid Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early syna ...
species, the cervical vertebrae bear
cervical rib A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% to 0.5% (1 in 200 to 500) of the ...
s. In
lizard Lizards are a widespread group of Squamata, squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbae ...
s and
saurischia Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithis ...
n dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other
amniote Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are distin ...
s. Most mammals have seven cervical vertebrae, with the only three known exceptions being the
manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living species ...
with six, the
two-toed sloth ''Choloepus'' is a genus of xenarthran mammals of Central and South America within the monotypic family Choloepodidae, consisting of two-toed sloths, sometimes also called two-fingered sloths. The two species of ''Choloepus'' (which means "lame ...
with five or six, and the
three-toed sloth The three-toed or three-fingered sloths are arboreal neotropical mammals . They are the only members of the genus ''Bradypus'' and the family Bradypodidae. The four living species of three-toed sloths are the brown-throated sloth, the maned sloth ...
with nine. In humans, cervical vertebrae are the smallest of the true vertebrae and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a
foramen In anatomy and osteology, a foramen (;Entry "foramen"
in
(hole) in each transverse process, through which the
vertebral artery The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline ...
,
vertebral veins The vertebral vein is formed in the suboccipital triangle, from numerous small tributaries which spring from the internal vertebral venous plexuses and issue from the vertebral canal above the posterior arch of the atlas. They unite with small v ...
, and
inferior cervical ganglion The inferior cervical ganglion is situated between the base of the transverse process of the last cervical vertebra and the neck of the first rib, on the medial side of the costocervical artery. Its form is irregular; it is larger in size than th ...
pass. The remainder of this article focuses upon human anatomy.


Structure

By convention, the cervical
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e are numbered, with the first one (C1) closest to the skull and higher numbered vertebrae (C2–C7) proceeding away from the skull and down the spine. The general characteristics of the third through sixth cervical vertebrae are described here. The first, second, and seventh vertebrae are extraordinary, and are detailed later. * The bodies of these four vertebrae are small, and broader from side to side than from front to back. ** The ''anterior'' and ''posterior surfaces'' are flattened and of equal depth; the former is placed on a lower level than the latter, and its inferior border is prolonged downward, so as to overlap the upper and forepart of the vertebra below. ** The ''upper surface'' is concave transversely, and presents a projecting lip on either side. ** The ''lower surface'' is concave from front to back, convex from side to side, and presents laterally shallow concavities that receive the corresponding projecting lips of the underlying vertebra. * The pedicles are directed laterally and backward, and attach to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time, narrower. * The laminae are narrow and thinner above than below; the
vertebral foramen In a typical vertebra, the vertebral foramen is the foramen (opening) formed by the anterior segment (the body), and the posterior part, the vertebral arch. The vertebral foramen begins at cervical vertebra #1 (C1 or atlas) and continues inferior ...
is large and of a triangular form. * The
spinous process The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...
is short and bifid, the two divisions being often of unequal size. Because the spinous processes are so short, certain superficial muscles (the
trapezius The trapezius is a large paired trapezoid-shaped surface muscle that extends longitudinally from the occipital bone to the lower thoracic vertebrae of the spine and laterally to the spine of the scapula. It moves the scapula and supports the ...
and
splenius capitis The splenius capitis () () is a broad, straplike muscle in the back of the neck. It pulls on the base of the skull from the vertebrae in the neck and upper thorax. It is involved in movements such as shaking the head. Structure It arises from t ...
) attach to the
nuchal ligament The nuchal ligament is a ligament at the back of the neck that is continuous with the supraspinous ligament. Structure The nuchal ligament extends from the external occipital protuberance on the skull and median nuchal line to the spinous process ...
rather than directly to the vertebrae; the nuchal ligament itself attaching to the spinous processes of C2–C7 and to the posterior tubercle of the atlas. * The superior and inferior
articular processes The articular processes or zygapophyses (Greek ζυγον = "yoke" (because it links two vertebrae) + απο = "away" + φυσις = "process") of a vertebra are projections of the vertebra that serve the purpose of fitting with an adjacent vertebr ...
of cervical vertebrae have fused on either or both sides to form articular pillars, columns of bone that project laterally from the junction of the pedicle and lamina. * The
articular facets A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
are flat and of an oval form: ** the ''superior'' face backward, upward, and slightly medially. ** the ''inferior'' face forward, downward, and slightly laterally. * The
transverse processes The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...
are each pierced by the foramen transversarium, which, in the upper six vertebrae, gives passage to the
vertebral artery The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline ...
and
vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...
, as well as a plexus of sympathetic nerves. Each process consists of an anterior and a posterior part. These two parts are joined, outside the foramen, by a bar of bone that exhibits a deep sulcus on its upper surface for the passage of the corresponding
spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
. ** The anterior portion is the homologue of the
rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ch ...
in the
thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
region, and is therefore named the ''costal process'' or ''costal element''. It arises from the side of the body, is directed laterally in front of the foramen, and ends in a tubercle, the anterior tubercle. ** The posterior part, the true transverse process, springs from the vertebral arch behind the foramen and is directed forward and laterally; it ends in a flattened vertical tubercle, the posterior tubercle. The anterior tubercle of the sixth cervical vertebra is known as the carotid tubercle or Chassaignac tubercle (for Édouard Chassaignac). This separates the carotid artery from the
vertebral artery The vertebral arteries are major arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, midline ...
and the carotid artery can be massaged against this tubercle to relieve the symptoms of
supraventricular tachycardia Supraventricular tachycardia (SVT) is an umbrella term for fast heart rhythms arising from the upper part of the heart. This is in contrast to the other group of fast heart rhythms – ventricular tachycardia, which start within the lower cha ...
. The carotid tubercle is also used as a landmark for
anaesthesia Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), a ...
of the
brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...
and
cervical plexus The cervical plexus is a plexus of the anterior rami of the first four cervical spinal nerves which arise from C1 to C4 cervical segment in the neck. They are located laterally to the transverse processes between prevertebral muscles from the me ...
. The cervical spinal nerves emerge from above the cervical vertebrae. For example, the cervical spinal nerve 3 (C3) passes above C3.


Atlas and axis

The
atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographi ...
(C1) and
axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...
(C2) are the two topmost vertebrae. The atlas (C1) is the topmost vertebra, and along with the axis forms the joint connecting the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
and spine. It lacks a vertebral body, spinous process, and discs either superior or inferior to it. It is ring-like and consists of an anterior arch, posterior arch, and two lateral masses. The axis (C2) forms the pivot on which the atlas rotates. The most distinctive characteristic of this bone is the strong odontoid process (dens) that rises perpendicularly from the upper surface of the body and articulates with C1. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and front part of the third vertebra.


Vertebra prominens

The vertebra prominens, or C7, has a distinctive long and prominent spinous process, which is palpable from the skin surface. Sometimes, the seventh cervical vertebra is associated with an abnormal extra rib, known as a
cervical rib A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% to 0.5% (1 in 200 to 500) of the ...
, which develops from the anterior root of the transverse process. These ribs are usually small, but may occasionally compress blood vessels (such as the
subclavian artery In human anatomy, the subclavian arteries are paired major arteries of the upper thorax, below the clavicle. They receive blood from the aortic arch. The left subclavian artery supplies blood to the left arm and the right subclavian artery suppl ...
or
subclavian vein The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorptio ...
) or nerves in the
brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...
, causing pain, numbness, tingling, and weakness in the upper limb, a condition known as thoracic outlet syndrome. Very rarely, this rib occurs in a pair. The long spinous process of C7 is thick and nearly horizontal in direction. It is not bifurcated, and ends in a tubercle that the
ligamentum nuchae The nuchal ligament is a ligament at the back of the neck that is continuous with the supraspinous ligament. Structure The nuchal ligament extends from the external occipital protuberance on the skull and median nuchal line to the spinous process ...
attaches to. This process is not always the most prominent of the spinous processes, being found only about 70% of the time, C6 or T1 can sometimes be the most prominent. The transverse processes are of considerable size; their posterior roots are large and prominent, while the anterior are small and faintly marked. The upper surface of each usually has a shallow sulcus for the eighth spinal nerve, and its extremity seldom presents more than a trace of bifurcation. The transverse foramen may be as large as that in the other cervical vertebrae, but it is generally smaller on one or both sides; occasionally, it is double, and sometimes it is absent. On the left side, it occasionally gives passage to the vertebral artery; more frequently, the vertebral vein traverses it on both sides, but the usual arrangement is for both artery and vein to pass in front of the transverse process, not through the foramen.


Function

The movement of nodding the head takes place predominantly through
flexion Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relativ ...
and extension at the
atlanto-occipital joint The atlanto-occipital joint (''Capsula articularis atlantooccipitalis'') is an articulation between the atlas bone and the occipital bone. It consists of a pair of condyloid joints. It is a synovial joint. Structure The atlanto-occipital join ...
between the atlas and the
occipital bone The occipital bone () is a cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone overlies the occipital lobes of the ce ...
. However, the cervical spine is comparatively mobile, and some component of this movement is due to flexion and extension of the vertebral column itself. This movement between the atlas and occipital bone is often referred to as the "yes joint", owing to its nature of being able to move the head in an up-and-down fashion. The movement of shaking or rotating the head left and right happens almost entirely at the joint between the atlas and the axis, the
atlanto-axial joint The atlanto-axial joint is a joint in the upper part of the neck between the atlas bone and the axis bone, which are the first and second cervical vertebrae. It is a pivot joint. Structure The atlanto-axial joint is a joint between the atlas ...
. A small amount of rotation of the vertebral column itself contributes to the movement. This movement between the atlas and axis is often referred to as the "no joint", owing to its nature of being able to rotate the head in a side-to-side fashion.


Clinical significance

Cervical degenerative changes arise from conditions such as
spondylosis Spondylosis is the degeneration of the vertebral column from any cause. In the more narrow sense it refers to spinal osteoarthritis, the age-related wear and tear of the spinal column, which is the most common cause of spondylosis. The degenera ...
,
stenosis A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture). ''Stricture ...
of intervertebral discs, and the formation of
osteophyte Osteophytes are exostoses (bony projections) that form along joint margins. They should not be confused with enthesophytes, which are bony projections that form at the attachment of a tendon or ligament. Osteophytes are not always distinguished ...
s. The changes are seen on
radiograph Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography ("diagnostic" and "therapeut ...
s, which are used in a grading system from 0–4 ranging from no changes (0) to early with minimal development of osteophytes (1) to mild with definite osteophytes (2) to moderate with additional disc space
stenosis A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture). ''Stricture ...
or narrowing (3) to the stage of many large osteophytes, severe narrowing of the disc space, and more severe vertebral end plate sclerosis (4). Injuries to the cervical spine are common at the level of the second cervical vertebrae, but neurological injury is uncommon. C4 and C5 are the areas that see the highest amount of cervical spine trauma. If it does occur, however, it may cause death or profound disability, including paralysis of the arms, legs, and diaphragm, which leads to
respiratory failure Respiratory failure results from inadequate gas exchange by the respiratory system, meaning that the arterial oxygen, carbon dioxide, or both cannot be kept at normal levels. A drop in the oxygen carried in the blood is known as hypoxemia; a rise ...
. Common patterns of injury include the odontoid fracture and the hangman's fracture, both of which are often treated with immobilization in a
cervical collar A cervical collar, also known as a neck brace, is a medical device used to support and immobilize a person's neck. It is also applied by emergency personnel to those who have had traumatic head or neck injuries, and can be used to treat chronic m ...
or
Halo brace Halo, halos or haloes usually refer to: * Halo (optical phenomenon) * Halo (religious iconography), a ring of light around the image of a head HALO, halo, halos or haloes may also refer to: Arts and entertainment Video games * ''Halo'' (franch ...
. A common practice is to immobilize a patient's cervical spine to prevent further damage during transport to hospital. This practice has come under review recently as incidence rates of unstable spinal trauma can be as low as 2% in immobilized patients. In
clearing the cervical spine Clearing the cervical spine is the process by which medical professionals determine whether cervical spine injuries exist, mainly regarding cervical fracture. It is generally performed in cases of major trauma. This process can take place in the ...
, Canadian studies have developed the Canadian C-Spine Rule (CCR) for physicians to decide who should receive radiological imaging.


Landmarks

The vertebral column is often used as a marker of
human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a head, ...
. This includes: * At C1, base of the
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes th ...
and the
hard palate The hard palate is a thin horizontal bony plate made up of two bones of the facial skeleton, located in the roof of the mouth. The bones are the palatine process of the maxilla and the horizontal plate of palatine bone. The hard palate spans ...
* At C2, the
teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tea ...
of a closed mouth * At C3, the
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
and
hyoid bone The hyoid bone (lingual bone or tongue-bone) () is a horseshoe-shaped bone situated in the anterior midline of the neck between the chin and the thyroid cartilage. At rest, it lies between the base of the mandible and the third cervical ver ...
* At C4, the
common carotid artery In anatomy, the left and right common carotid arteries (carotids) (Entry "carotid"
in
thyroid cartilage The thyroid cartilage is the largest of the nine cartilages that make up the ''laryngeal skeleton'', the cartilage structure in and around the trachea that contains the larynx. It does not completely encircle the larynx (only the cricoid cartilage ...
* From C6–7, the
cricoid cartilage The cricoid cartilage , or simply cricoid (from the Greek ''krikoeides'' meaning "ring-shaped") or cricoid ring, is the only complete ring of cartilage around the trachea. It forms the back part of the voice box and functions as an attachment sit ...
* At C6, the
oesophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
becomes continuous with the
laryngopharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struct ...
and also where the
larynx The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...
becomes continuous with the
trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from the la ...
. It is also the level where the
carotid In anatomy, the left and right common carotid arteries (carotids) (Entry "carotid"
in
Scrollable computed tomography images of normal cervical vertebrae File:Cervical vertebrae animation small.gif, Position of cervical vertebrae (shown in red). Animation. File:Blausen 0222 CervicalSpine.png, Illustration of cervical vertebrae File:Cervical vertebrae - close-up - animation2.gif, Shape of cervical vertebrae (shown in blue and yellow). Animation. File:Human cervical vertebra.stl, 3D image File:Cervical vertebrae lateral3.png, Cervical vertebrae, lateral view (shown in blue and yellow) File:Illu vertebral column.svg, Vertebral column File:Gray 111 - Vertebral column-coloured.png, Vertebral column File:HWS seitlich Annotation.jpg, X-ray of cervical vertebrae File:Cervical XRayFlexionExtension.jpg, X-ray of cervical spine in flexion and extension File:Gray86.png, First cervical vertebra, or atlas File:Gray87.png, Second cervical vertebra, or epistropheus, from above File:Gray88.png, Second cervical vertebra, epistropheus, or axis, from the side File:Gray89.png, Seventh cervical vertebra File:Gray305.png, Posterior atlanto-occipital membrane and atlantoaxial ligament File:Gray308.png, Median sagittal section through the occipital bone and first three cervical vertebrae File:Gray384.png, Section of the neck at about the level of the sixth cervical vertebra File:Cervical Spine Anterior View.png, Anterior view of cervical spine showing the vertebral arteries along with the spinal nerves. See this in 3
here.


See also

* Vertebral column *
Cervical fracture A cervical fracture, commonly called a broken neck, is a fracture of any of the seven cervical vertebrae in the neck. Examples of common causes in humans are traffic collisions and diving into shallow water. Abnormal movement of neck bones or pie ...


References


External links


Diagram
at kenyon.edu


Mnemonic for Landmarks

Cervical vertebra quiz

Cervical vertebrae
- BlueLink Anatomy - University of Michigan Medical School {{DEFAULTSORT:Cervical Vertebrae Bones of the head and neck Bones of the thorax Bones of the vertebral column