The Vertebral Column, Thorax, and Skull Anatomy

The Vertebral Column: Bones and Joints

Vertebrae: 33 bones in the vertebral column.
- Cervical vertebrae: 7 bones in the neck.
- Thoracic vertebrae: 12 bones in the thorax.
- Lumbar vertebrae: 5 bones behind the abdomen.
- Sacrum: 5 fused bones in the pelvis (sacra, sacral).
- Coccyx: 4 or 3 or 5 incomplete bones (coccygeal).

Joints of the Vertebral Column

Intervertebral joints (discs): Located between adjacent vertebrae.
Interarticular joints: Located between articular processes.
Atlantooccipital joints: Between the occipital bone and atlas.
Atlantoaxial joints: Three joints
- Median: One
- Lateral: Two
Lumbosacral joint: One, between the 5th lumbar vertebra & sacrum.
Sacrococcygeal joint: One, between sacrum and coccyx.
Costovertebral joints: Between a rib and a vertebra.
Costotransverse joints: Between tubercle of a rib & transverse process of vertebra.

Divisions and Curvatures of the Vertebral Column

Cervical vertebrae: Seven in the neck.
Thoracic vertebrae: Twelve in the thorax.
Lumbar vertebrae: Five behind the abdomen.
Sacrum: Five fused vertebrae, in the pelvis.
Coccyx: Possibly 3 or 4 or 5 vertebrae in the pelvis.
Normal Curvatures:
- Cervical curvature: Lordotic type.
- Thoracic curvature: Kyphotic type.
- Lumbar curvature: Lordotic type.
- Pelvic curvature: Kyphotic type.

Structure of Vertebrae

Body
Arch: Two pedicles (right & left), two laminae (plates, right & left).
Seven processes:
- Two transverse (right & left)
- Two superior articular (right & left)
- Two inferior articular (right & left)
- One spinous process
Vertebral arch: One
Vertebral canal: One
Vertebral notches: Four (two superior, two inferior)
Intervertebral foramina: Two (right & left)

Identifying Characteristics of Vertebrae

True (movable) vertebrae
False (fixed) vertebrae
Cervical:
- Forked spinous processes.
- Foramina transversaria (two, right & left).
- Atlas (first cervical vertebra): No body, two arches (anterior, posterior).
- Axis (second cervical vertebra): Dens or odontoid process.
- Vertebra prominens (C7): Large, long spinous process.
Thoracic:
- Costal pits or foveae:
  - On vertebral body: 2 or 4 (right & left)
  - On transverse processes: 2 (right & left)
Lumbar:
- Large size.
- No pits.
- No foramina transversaria.
Sacrum:
- Five fused bodies.
- Lateral parts fused.
- Alae (wings), base, apex, promontory.
- Superior articular processes (right & left).
- Sacral canal, hiatus & two cornua.
- Sacral foramina: 8 anterior, 8 posterior.
Coccyx: 4 or 3, or 5 incomplete, 2 cornua.

Detailed Study of Vertebral Column Bones

Vertebrates: Animals with vertebral columns.
Vertebral column (backbone): Extends from the base of the skull to the tail bone.
Composition: 33 vertebrae
- True/Movable: 24 separate bones.
- False/Fixed: 5 fused to form the sacrum, 4 form the coccyx..

Divisions of the Vertebral Column

Five parts (cervical, thoracic, lumbar, sacrum, coccyx) named by location.
Vertebrae are further named by division and number (e.g., first cervical, second thoracic).

Curvatures of the Vertebral Column

Cervical: Lordotic curve with anterior convexity.
Thoracic: Kyphotic curve with anterior concavity and posterior convexity.
Lumbar: Lordotic curve, convex anterior.
Pelvic: Kyphotic curve, concave anterior; formed by sacrum and coccyx.

Structure of a Vertebra

Vertebra: A bone of the vertebral column
Vertebra has a body, arch, seven processes, and vertebral foramen.
1. Body: Solid, cylinder-shaped anterior part with a flattened posterior surface.
2. Arch: Curved posterior part enclosing an opening.
  - Pedicles: Two short rounded processes extending posteriorly from the body.
  - Laminae: Two flattened plates extending towards the midline from each pedicle, uniting to form the spinous process.
  - Vertebral foramen: Opening formed by the vertebral arch and posterior surface of the body.
  - Vertebral canal: Tubular passage from the foramen magnum to the lower sacrum, formed by vertebral foramina and ligaments.
  - Vertebral notch: Curved surface of a pedicle (superior and inferior).
  - Intervertebral foramen: Opening formed by an inferior notch of one vertebra and the superior notch of the vertebra below; spinal nerve exit.
3. Seven processes:
  - Transverse processes: Extend laterally from the junction of a pedicle with a lamina.
  - Superior articular processes: Extend upwards towards the head from the junction of each pedicle and lamina; surfaces directed somewhat posteriorly.
  - Inferior articular processes: Project caudally (downwards) from the junction of each pedicle and lamina; surfaces directed anteriorly; form joints with the superior articular processes of the vertebra below.
Composition: Bodies are cancellous (spongy) bone with a thin covering of compact bone; arches/processes have a core of cancellous bone with an outer layer of compact bone.

Characteristics That Identify Vertebrae

Vertebrae become larger from cervical to lumbar.
Cervical:
- Small; spinous processes are usually forked (bifid or double).
- Foramen transversarium (transverse foramen): Opening in each transverse process for vertebral artery to reach the skull.
- Superior/inferior articular processes form a pillar or column of bone behind the transverse process.
- Articular facets (foveae) are inclined slightly posteriorly from the horizontal.
Atlas (first cervical vertebra):
- No body and no spinous process.
- Two lateral masses of bone and two arches.
- Lateral masses: Support articular facets (foveae) and are joined by anterior/posterior arches.
- Vertebral foramen: Large, formed by anterior arch, lateral mass, and posterior arch.
- Transverse ligament: Divides foramen into two parts (dens/odontoid process and spinal cord).
- Superior articular facets: Articulate with a condyle of the occipital bone.
- Inferior articular facets: Articulate with the superior articular processes of the second cervical vertebra.
Axis (second cervical vertebra):
- Dens or odontoid process: Tooth-shaped process extending upwards from its body; fits into anterior arch of the atlas above.
- Forms a pivot joint with the atlas, allowing head rotation.
Thoracic:
- Larger than cervical.
- Spinous processes directed almost vertically caudally.
- Costal pits (foveae): Depressions for articulation with ribs
  - Costal pit of a thoracic vertebra, or a facet, lies on the lateral surface of a thoracic vertebra close to its posterior margin, to articulate with the head of a rib. As some vertebrae articulate with two ribs there are two semilunar pits, one on the upper and the other on the lower margin, rather than one circular pit at the center of the body. The tenth, eleventh, and twelfth vertebrae have a single pit on each side as they form joints with one rib only.
  - Costal pit on a transverse process: this rounded pit lies on the anterior surface of a transverse process of thoracic vertebrae. If forms a joint with a tubercle of a rib.
Lumbar:
- Larger than thoracic and become progressively larger toward sacrum.
- Spinous processes directed almost horizontally and posteriorly.
- No foramina and no costal pits.
Sacrum:
- Five vertebrae united to form a single bone.
- Sacral segments separated by cartilages in fetus/young child.
- Body of the sacrum or central part is the large curved area that is formed from the fused bodies of the five sacral segments.
  - The transverse ridges on the pelvic (anterior) surfaces at each level denote the points of union of these segments.
- Lateral parts (lateral masses) lie on either side of fused bodies.
- Ala is the winglike upper part of each lateral mass.
- Base is its broad upper end consisting of the upper surface of the body of the first sacral segment and the alae on either side.
- Promontory is the prominent anterior margin of the upper sacral segment.
- Superior articular processes extend up from the posterolateral margins.
- Apex is its small inferior end which articulates with the first segment of the coccyx.
- Sacral canal is a tubelike passage that extends through the sacrum from top to bottom. The vertebral foramina of the original vertebrae have formed this channel with the fused bodies in front and the fused arches behind. The sacral and coccygeal nerves pass down in this canal.
- Sacral hiatus is an opening in the sacral canal posteriorly at its lower end, causing a gap between the laminae of the fifth sacral segment.
- Sacral cornua are two small bony projections that extend caudally from the lower sacrum posteriorly, one on each side of the sacral hiatus. They form joints with similar cornua of the coccyx.
- Dorsal sacral foramina open into the canal on either side. They lie lateral to the fused bodies and transmit the dorsal branches of the sacral nerves from the sacral canal.
- Pelvic (anterior) sacral foramina open into the sacral canal on each side from the pelvic surface of the sacrum. They transmit anterior branches of the sacral nerves to the pelvis.
- Auricular surfaces are located one on each lateral surface of the sacrum. These rough areas join the auricular surfaces of the iliac bones to form the sacroiliac joints.
Coccyx:
- Usually formed by four (or occasionally three, or five) incompletely developed vertebrae; segments often remain separate.
- Upper end forms a joint with the apex of the sacrum.
- Cornua are two small bony processes that extend up from the posterior surface of the coccyx to meet similar cornua of the sacrum.
The vertebra prominens or seventh cervical vertebra has a longer and larger spinous process than the other cervical vertebra. It is readily palpable at the base of the neck posteriorly.

Joints of the Vertebral Column- Detailed Study

Intervertebral joints (Intervertebral discs):
- Intervertebral joints are located between bodies of adjacent vertebrae from the second cervical vertebra to the lumbosacral joint (5th lumbar and sacrum).
  - These are cartilaginous joints permitting slight flexion, extension, lateral flexion, rotation and some circumduction.
  - Movement at one joint is limited, but numerous joints allow significant movement.
  - Most movement in cervical and lumbar, minimal in the thoracic part.
- Formed by:
  - Articular surfaces covered by compact bone;
  - Articular cartilages of hyaline cartilage;
  - Intervertebral disc:
    - Anulus fibrosus (outer pad of fibrous tissue and fibrocartilage);
    - Nucleus pulposus (pulpy center of a disc in the center of an anulus fibrosus).
  - Ligamenta:
    - Anterior and posterior longitudinal ligaments (lengthwise along surfaces);
    - Ligamenta flava (between the laminae of adjacent vertebrae);
    - Interspinal ligaments (connect adjacent spinous processes);
    - Supraspinatus ligament (connects the tips of the spinous processes).
      *Interarticular joints (Zygapophyseal joints):
- Right and left joints located between articular processes of adjacent vertebrae on each side.
- Inferior articular process of one vertebra articulating with the superior articular process below.
- Synovial gliding joints.
Atlantooccipital joints:
- Two joints, right and left, located between the atlas and occipital bone.
- Occipital condyle of the occipital bone articulating with the superior articular surface on the lateral mass of the atlas.
  - Synovial condylar joints, permitting flexion, extension, and slight lateral flexion.
Atlantoaxial joints:
- One median and two lateral joints located between the atlas and axis.
  - Median atlantoaxial joint is between the dens (odontoid process) of the axis and a ring formed by the anterior arch of the atlas and its transverse ligament.
    - Synovial pivot joint with two synovial cavities, permitting rotation of atlas and head upon the axis.
  - Lateral atlantoaxial joints are located between inferior articular surface of the lateral mass of the atlas and the superior articular process of the axis.
    - Synovial gliding joints.
      *Accessory cervical joints:
- Located between the lateral margins of articular surfaces of lower cervical vertebrae.
Lumbosacral joint:
- Single joint located between fifth lumbar vertebra and the upper end of sacrum.
- Inferior articular surface of the fifth lumbar vertebra and the superior articular surface of the sacrum creating a cartilaginous joint with an intervertebral disc.
Sacrococcygeal joint:
- Located between Sacrum and Coccyx.
- Distal end of sacrum and first segment of the coccyx creates a cartilaginous joint with a disc.

Congenital Anomalies of Vertebrae

Fusion of vertebrae: Two or more vertebrae are united without a joint between them.
Hemivertebra: The right or left half of a vertebra may be absent, or one half of a vertebra may fuse with the vertebra above or below it, leaving the other half as a separate bone.
Spina bifida: The right and left laminae may fail to unite with each other at the median line posteriorly.
Articular defects: Defects that may be present between the superior and inferior articular processes of a vertebrae at the isthmus where these join.
Absence of sacrum: The lower part of the sacrum may fail to develop:
Sacralization: The fifth lumbar vertebra may be partly or completely fused with the upper sacrum.

Landmarks and Prominences of Vertebrae

Spinous processes: Readily palpable in the midline posteriorly.
Spinous process of seventh cervical vertebra: Large and readily palpable at base of the neck.
The spinous processes of the thoracic vertebrae lie at a lower level than the corresponding vertebral bodies.
Sacrum and coccyx: Palpable through crease between buttocks and via rectal examination.
Locating a lumbar vertebra on a processed film; when the lumbosacral joint is not included on the radiograph the twelfth thoracic vertebra may be determined as that to which the last rib is attached.
Surface markings on anterior body surface corresponding to various vertebrae:
- Hard palate - 1st cervical vertebra
- Hyoid bone - 2nd or 3rd cervical vertebrae
- Thyroid cartilage - upper margin C4
- Cricoid cartilage - cervical 6
- Jugular notch between T2 and T3
- Sternal angle - joint between T4 and T5
- Xiphisternal junction - joint between T9 and 10
- Transpyloric plane - Li
- Subcostal plane - L3
- Umbilicus-joint between L3 and LA
- Iliac crests - L5
- Anterior superior spine - 2nd sacral segment.

Anatomical Peculiarities and Radiography

Curvatures of the vertebral column: The cervical and lumbar lordotic curves, and the thoracic and pelvic kyphotic curves, should be noted.
In the cervical area flexing the head upon the chest will obliterate the curve, but the facial bones will then obscure the lower cervical bodies. If the mouth be opened the upper cervical vertebrae will become visible.
The thoracic vertebrae have limited movement and it may be impossible to get rid of the kyphotic curve.
The lumbar vertebrae are quite movable. If a hand be placed upon the table top under the lumbar vertebrae, with the subject supine, the midlumbar vertebrae will not be touching the table.
The interarticular joints lie obliquely to the sagittal plane so that it is not possible to see through them with the subject supine.
The sacrum and coccyx form the pelvic curve and appear to be foreshortened when viewed with the eye at their level.
The lumbosacral joint is directed obliguely and cannot be seen without overlapping of bones in the supine position.
Scoliosis of the vertebral column is a curvature in a lateral direction to the right or left. It does not occur normally.

Anatomical Terms Used in Studying the Vertebral Column

anulus fibrosus
apophyseal joint
zygapophyseal joint
arch of a vertebra
articular cartilage
of a vertebra
atlas
atlantooccipital joint
axis
atlantoaxial joint
body of a vertebra
cervical vertebra
coccyx
coccygeal
congenital anomaly
cornu, cornua
cornu of coccyx
cornu of sacrum
dens or
odontoid process
dorsal vertebra
facet of vertebra
facet of rib
foramen, foramina
foramen transversarium
fovea = a pit
hemivertebra
inferior articular
process
interarticular isthmus
interarticular joints
intervertebral foramen
kyphosis
kyphotic
lamina, laminae
lordosis
lordotic
lumbar vertebra
lumbosacral joint
nucleus pulposus
pedicle of vertebra
sacrum, sacra, sacral
sacrococcygeal joint
sacroiliac joint
sacrovertebral joint
scoliosis
scoliotic
spina bifida
spinous process of a
vertebra
superior articular
process
thoracic vertebra
vertebra, vertebrae
vertebral
vertebral foramen
vertebral foramina
vertebral notch
vertebral prominens

The Thorax: Bones and Joints

Thoracic vertebrae - 12
- See vertebral column
Sternum-breast bone-one only
Ribs or costae-12 pairs, right, left
Costal cartilages - 12 pairs right and left

Joints of the Thorax

Costovertebral-between a rib and the body of a vertebra
Costotransverse - between a rib and a transverse process of a vertebra
Sternocostal or costosternal between a rib cartilage and the sternum
Costochondral - between a rib and its costal cartilage
Interchondral-between the adjacent anterior margins of costal cartilages of sixth to tenth ribs
Sternoclavicular- between the sternum and the clavicle
Manubriosternal-between the manubrium and the body of the sternum
Xiphisternal-between the body of the sternum and its xiphoid process

Parts and Prominences of Bones of Thorax

Thoracic vertebrae
- See S. 88, 89
Sternum a flat bone
1. Manubrium:
  - jugular notch (suprasternal notch)
  - clavicular notches
  - costal notches, complete and half, Rt. Lt.
2. Body or gladiolus;
  - costal notches-4 and 2 half notches, Rt. Lt.
3. Xiphoid process - one half notch, Rt. Lt.
Ribs (costae) 12 pairs - right and left:
1. dorsal extremity or vertebral extremity (end)
  - with a head neck and tubercle
2. body or shaft
  - with an angle
3. ventral extremity or sternal extremity
Costal cartilages - 12 pairs - right and left:
- seven upper ribs articulating with sternum separately
- eighth, ninth, tenth, join cartilage of rib above
- the eleventh and twelfth have free anterior ends so are floating
True and false ribs:
- true ribs-upper seven pairs
- false ribs lower five pairs
Alternate classification:
- vertebrosternal-upper seven pairs
- vertebrochondral ribs-eighth, ninth, tenth pairs
- vertebral ribs - eleventh and twelfth pairs

Detailed Study of the Bones of the Thorax

The thorax, the upper part of the trunk, is a cage composed of bones and cartilages
- affords protection for several very vital organs: the heart with its trunk vessels and the respiratory organs.
The skeleton of the thorax includes:
- twelve thoracic vertebrae
- the sternum
- twelve pairs of ribs
- twelve pairs of costal cartilages
The thoracic vertebrae have been studied in the preceding chapter.
- the student should review these paragraphs dealing with the costal pits (fovea) on the vertebral bodies, and their transverse processes.

The Sternum

Sternum breast bone
The sternum is a long flat bone that lies vertically in the midline of the anterior chest wall.
Because this bone is shaped somewhat like a sword or dagger
- its parts have been given names similar to the parts of a sword - a handle, blade and point.
The sternum has a manubrium, a body, and a xiphoid process.
1. The manubrium of the sternum is its upper part and represents the handle of the sword.
  - The manubrium is separated from the body of the sternum by cartilage.
  - In later life these two parts may fuse.
  - The manubrium has a jugular notch, clavicular notches and costal notches.
  - The jugular notch formerly named the suprasternal notch (OT) is a depression on the upper surface of the manubrium of the sternum.
  - The clavicular notches, a right and a left, are placed obliquely on either side of the jugular notch.
    - They form joints with the medial ends of the clavicles -the sternoclavicular joints.
2. The body or gladiolus of the sternum extends from the manubrium to the xiphoid process below and is the largest part of the sternum.
  - It consists of four segments formed from separate centers of ossification.
  - They unite during adolescence to form a single bone.
  - The body has costal notches.
3. The xiphoid process of the sternum is the inferior part of the bone.
  - Composed of cartilage in the young it becomes ossified and often fuses with the body above.
The costal notches are niches on the lateral margins of the sternum that articulate with the medial ends of the costal cartilages.
- The manubrium has one complete notch, and one half-notch on either side.
- The body has four complete notches and an upper and a lower half-notch on either side.
- The xiphoid has a half-notch to complete the notch for the seventh rib bilaterally.

The Ribs

There are twelve pairs of ribs, twelve left, and twelve right.
Each rib is attached to a costal cartilage at its anterior end.
The ribs are long, curved, flat bones that form the posterior wall, the lateral walls, and part of the anterior wall of the thorax.
From above down the ribs are named as the first, second, third, etc., and as right or left.
Each rib has a dorsal or vertebral extremity or end, a body, and a ventral or sternal extremity or end.
1. The dorsal extremity has a head, a neck, and a tubercle.
  - The head of a rib is its slightly expanded posterior end; has one or two articular surfaces (facets) depending on whether it articulates with one or two vertebral bodies.
  - The neck of a rib is its slightly constricted part connecting the head to the body.
  - The tubercle of a rib is a small prominence on the dorsal surface at the junction of the neck and body; has a small articular surface (facet) that forms a joint with a transverse process of a vertebra.
2. The body of a rib is the long, flat, curved part that extends from the neck around the chest wall; at its lower margin there is a groove (costal groove) for an intercostal artery, vein, and nerve.
  - The angle of a rib is a prominence in front of the neck where the rib becomes bent anteriorly.
3. The ventral or sternal extremity is the anterior end that articulates with its costal cartilage.
The ribs become longer from the first to the seventh, then shorter until the eleventh and twelfth end in the lateral or posterior abdominal wall.
- The first rib has two grooves running transversely on its upper anterior surface for the subclavian artery and vein.
- The first, tenth, eleventh, and twelfth ribs have a single articular surface on the head.
- The eleventh and twelfth ribs have no tubercles.

The Costal Cartilages

There are twelve pairs of costal cartilages, one attached to the sternal end of each rib.
These cartilages are flat plates of cartilage similar in shape to the adjacent rib.
The lateral end of each costal cartilage articulates with the anterior end of the corresponding rib.
The medial end of each of the upper seven costal cartilages on each side articulates separately with a costal notch on the sternum.
The medial end of each of the eight, ninth, and tenth costal cartilages articulates with the lower margin of the costal cartilage above it.
The anterior ends of the costal cartilages of the eleventh and twelfth ribs end in the upper lateral abdominal wall.
Costal cartilages become progressively longer from the first to the seventh, then shorter.
The costal arch is the curve formed by the anterior margins of the seventh, eighth, ninth and tenth costal cartilages on each side and the rounded tip of the xiphoid process.

True Ribs and False Ribs

Ribs are frequently classified as true and false ribs.
- This division depends upon whether or not the anterior end of the rib joins the sternum.
- All ribs articulate posteriorly with vertebrae.
True ribs: the upper seven pairs articulate by means of their costal cartilages with the sternum at a costal notch.
- named vertebrosternal ribs
The false ribs: the lower five pairs do not articulate with the sternum.
- vertebrochondral ribs:the upper 3 pairs of false ribs, the eighth, ninth, and tenth ribs have costal cartilages that are joined to the costal cartilages above (vertebra + chondros, a cartilage)
- vertebral ribs, or floating ribs: the lower two pairs, the eleventh and twelfth have no connection with the sternum.

Structures Forming the Joints of the Thorax

Refer to list of joints and the structures forming each joint.

Detailed study of the Joints of the Thorax

Intervertebral and interarticular joints of the vertebrae have been described along with the other joints of the vertebral column.
- The student should review the following terms:
  - Fovea a small pit or depression at a joint,
  - Facet a small smooth articular surface,
  - Articular surface a smooth bone surface that helps to form a joint.
Costovertebral joints
- There are two types of joints between the thoracic vertebrae and ribs: joints of the heads of ribs and vertebral bodies; costotransverse joints between the tubercles of ribs and transverse processes of vertebrae.
  1. Joints of heads of ribs and vertebral bodies.
    - The articular surface of the head of a rib articulates with a pit (fovea) on the lateral surface of the body of a vertebra.
    - The first, tenth, eleventh, and twelfth vertebral bodies have a single pit on the lateral surface of the body on each side, that articulates with the head of a single rib.
    - Synovial joints, permitting slight movement.
  2. Costotransverse joints:
    - Location-between ribs and transverse processes of vertebrae.
    - Formed by pit or fovea on anterior surface of transverse process of thoracic vertebra, and a small facet (articular surface) on the tubercle of a rib, except for 11th and 12th ribs.
    - Synovial gliding joints, permitting slight movement.
Costochondral joints:
- Located at the anterior, or sternal, end of a rib and the adjacent costal cartilage.
Sternocostal or Costosternal joints:
- Located at the lateral margins of the sternum on each side.
Located at the anterior, or sternal, end of a rib and the adjacent costal cartilage.

Interchondral joints:
- Located between adjacent anterior margins of the seventh, eighth, ninth, and tenth costal cartilages and the rib cartilage above each one.

Sternoclavicular joints:
- Two, one right, one left.

Manubriosternal joint: one only.
- Located between the inferior margin of the manubrium and the upper margin of the body of the sternum, at the sternal angle.
- A cartilaginous joint, frequently ossified in later life.

Xiphisternal or Xiphosternal Joint: one only.

Located between the inferior end of the body of the sternum and the xiphoid process of the sternum.

Congenital Anomalies of the Bones of the Thorax

Cervical ribs: An extra rib may be present on one or both sides above the first rib.
Lumbar ribs: short extra ribs may be present below the twelfth ribs, they join the first lumbar vertebra.
Forked rib: The anterior or sternal end of a rib may divide into two parts.
Fused ribs: Two adjacent ribs may be joined for a part of their length.
Pectus excavatum: the sternum may be depressed so that it lies closer to the thoracic vertebrae than usual.
The reverse condition, that of a pigeon chest, with prominent sternum may be present.

Landmarks - Prominences of the Bones of the Chest

The jugular notch can be felt as a depression on the upper end of the sternum and is often visible.
The sternal angle is often visible and can be palpated as a ridge passing transversely across the upper sternum at the junction of the manubrium and body of the sternum.
The disc between the fourth and fifth thoracic vertebae is opposite the sternal angle in front
The xiphisternal joint can be felt at the lower end of the body of the sternum.
The costal arch is formed by the anterior margins of the 8th, 9th, and 10th costal cartilages and the tip of the xiphoid. The gall bladder often lies posterior to the right upper costal margin.

Thoracic Peculiarities and Radiography

A mounted skeleton should be viewed in the supine and prone positions to demonstrate the observations outlined here.
The sternum in the prone position is completely hidden by the thoracic vertebrae.
The sternoclavicular joints and medial ends of the clavicles are also obscured by the vertebrae unless an oblique position is assumed.
The ribs: if viewed from the front or back the lateral parts appear to be foreshortened as they are directed anteroposteriorly. By rotating the subject into an oblique position these parts are visible face on.
The costal cartilages although visible in the skeleton are translucent and therefore not visible in radiographs unless they are calcified.

Terms Used in Study of the Thorax

angle of sternum
angle of a rib
body of sternum
cervical rib
chondrosternal joint
corpus sterni
costa, pl. costae
costal, adj.
costal cartilage
costotransverse joint
costosternal joint
costovertebral joint
costal arch
ensiform process
facet
false rib
fovea, foveae, a pit
gladiolus of sternum
head of rib
intercostal space
jugular notch
manubrium sterni
neck of rib
rib or costa
shaft or rib
sternum, pl. sterna
sternal, adj.
sternal angle
sternochondral joint
sternoclavicular joint
sternocostal joint
sternomanubrial joint
suprasternal notch
thorax, adj