Chapter 8 Flashcards
What are intervertebral disks?
Tough fibrocartilaginous disks separate typical adult vertebrae. These cushion like disks are tightly bound to the vertebrae for spinal stability, but allow for flexibility and movement of the vertebral column.
Cervical vertebrae
7
Thoracic Vertebrae
The next 12 vertebrae are the thoracic vertebrae, and each of these connects to a pair of ribs. Because all vertebrae are posterior or dorsal in the body.
Lumbar Vertebrae
The largest individual vertebrae are the five lumber vertebrae. These vertebrae are the strongest in the vertebral column because the load of body weight increases toward the inferior lumbar vertebrae are common sites of injury and pathology.
Sacrum and Coccyx
The sacrum and coccyx develop as multiple separate bones and then fuse into two distinct bones. A newborn has 5 sacral segments and from three to five (average, four) coccygeal segments, for an average of 33 separate bones in the vertebral column of a young child. The adult body has 26 bones.
Vertebral Column Curvatures
composed of a series of anterposterior curves. The terms conmcave (a rounded inward or depressed surface like cave) and convex (a rounded outward elevated surface) are used to describe these curves. The cervical and lumber regions have concave curvatures and are described as .lordotic. The thoracic and sacral region have convex curvatures.
Vertebral Column Curvatures
Soon after birth, the thoracic and sacral (pelvic) curves begin to develop. These two convex curves are called primary curves. As children begin to raise their head and sit up, the first compensatory concave curve forms in the cervical region. The second compensatory concave curve, the lumbar curvature, develops when children learn to walk.
Lordoses
abnormal anterior concavity of the lumber spine
kyphosis
abnormal condition characterized by increased convexity of the thoracic spine curvature
scoliosis
an exaggerated lateral curvature of the spine
typical vertebral anatomy
1) the body–thick, weight bearing anterior part of the vertebra. Its superior and inferior surfaces are flat and rough for attachment of the intervertebral disks. 2) vertebral arch– the second part consists of a ring or arch of bone that extends posteriorly from the vertebral body. The postereior surface of the body and arch form a circular opening, the vertebral foramen, which contains the spinal cord.
vertebral arch (superior perspective)
pedicles which extend posteriorly from either side of the vertebral body, form most of the sides of the vertebral arch. The posterior part of the vertebral arch is formed by two somewhat flat layers of bone called laminae. Each lamina extends posteriorly from each pedicle to unite in the midline. Extending laterally from approximately the junction of each pedicle and lamina is a projection termed the transverse process. The spinous process extends posteriorly at the midline junction of the two laminae. The spinous processes, the most posterior extensions of the vertebrae, can be palpated along the posterior surface of the neck and back.
summary of vertebral arch
the typical vertebra consists of two pedicles and two laminae that form the vertebral arch and the vertebral foramen containing the spinal cord, two transverse processes extending laterally, one spinous process extending posteriorly, and the large anterior body. Each typical vertebra also has four articular processes, two superior and two inferior, which comprise the important joints of the vertebral column.
vertebral anatomy
3) joints in the vertebral column
the vertebral column would be rigidly immovable without the intervertebral disks and the zygapophyseal joints. Respiration could not occur without the spine, which serves as a pivot point for archlike movement of the ribs.
joints in the vertebral column (intervertebral joints)
The intervertebral joints are ampiathrodial joints that are found between the vertebral bodies. The intervertebral joints provide spinal stability, but they also allow for flexibility and movement of the vertebral column.
joints in the vertebral column (zygapophyseal joints)
The four articular processes are seen projecting from the area of the junction of the pedicles and laminae. The term facet sometimes is used interchangeably with the term zygapophyseal joint, but the facet is actually only the articulating surface instead of the entire superior or inferior articular process.
joints in the vertebral column (costal joints)
not involved in the stability of the spinal column itself, a third type of joint is located along a portion of the vertebral column. In the thoracic region, the 12 ribs articulate with the transverse processes and vertebral bodies. These articulations of the ribs to the thoracic vertebra, referred to as costal joints.
typical vertebral anatomy- (intervertebral foramina)
along, the upper surface of each pedicle is a half moon shaped area termed the superior vertebral notch, and along the lower surface of each pedicle is another half moon shaped area called the inferior vertebral notch. When the vertibrae are stacked, the superior and inferior vertebral notches line up. These two half moon shaped areas form a single opening, the intervertebral foramen. Therefore, between every two vertebrae are two intervertebral foramina, one on each side, through which important spinal nerves and blood vessels pass.
typical vertebral anatomy- intervertebral disk
typical adult vertebrae are seperated by tough fibrocartilaginous disks between the bodies of every two vertebrae, except between the first and second cervical vertebrae. (The first cervical vertebrae has no body.) These fibrocartilage disks provide a resilient cushion between vertebrae, helping to absorb shock during movement of the spine. Each disks consists of an outer fibrous portion termed the annulus fibrosus and a soft, semigelatinous inner part termed the nucleus pulposus. When this soft inner part protrudes through the outer fibrous layer, it presses on the spinal cord and causes severe pain and numbness that radiates into the lower limbs. This condition is known as a slipped disk, is termed the herniated nucleus pulposus (HNP).
characteristics of cervical vetebrae
The cervical vertebrae show little resemblance to the lumbar or thoracic vertebrae, which are more typical in appearance. The unique characteristics of cervical vertebrae are transverse foramina, bifid spinous process tips, and overlapping vertebral bodies. Each cervical vertebrae and vertebral body continues to get larger, progressing down to the seventh cervical vertebra.
C1 (atlast) C2 (axis) are unusual. The 3rd through 6th cervical vertebrae, are typical cervical vertebrae. The last, or seventh, cervical vertebra, the vertebral prominens, has many thoracic vertebrae features, including an extra long and more horizontal spinous process (vertebral prominens).
characteristics of cervical vertebrae (superior perspective)
The transverse processes are small and arise from both the pedicle and the body, rather than from the pedicle-lamina junction. The hole in each transverse process is called a transverse foramen. The vertebral artery and veins and certain nerves pass through these successive transverse foramina. Therefore, one unique characteristic of all cervical vertebrae is that each has three foramina that run vertically, the right and left transverse foramina and the single large vertebral foramin. The spinous processes of c2 through c6 are fairly short and end in double pointed bifid, a second unique characteristic typical of cervical vertebrae.
characteristics of cervical vertebrae (lateral perspective) in shape, with the anterior edge slightly more inferior, which causes slight overlapping of the vertebral column
When viewed from the lateral perspective, typical c3-c6. Cervical vertibral bodies are small and oblong in shape, with the anterior edge slightly more inferior, which causes slight overlapping of the vertebral bodies.
Located behind the transverse process at the junction of the pedicle and lamina are the cervical articular processes. Between the superior and inferior articular processes is a short column (pillar) of bone that is more supportive than the similar area in the rest of the spinal column. This column of bone is called the articular pillar, sometimes called the lateral mass, when one is referring to C1.
cervical zygapophyseal joints
the superior and inferior articular processes, located rover and under the articular pillars, are directly lateral to the large vertebral foramen. The zyga joints of the second through seventh cervical vertebra are located at right angles, 90 degrees, to the midsagittal plane thus are visualized only in the true lateral position.
cervical intervertebral foramina
the intervertebral foramina can be identified by the pedicles, which form the superior and inferior boundaries of these foramina. The intervertebral foramina are situated at a 45 degree angle to the midsagittal plane, open anterirly. They also are directed at a 15 degree inferior angle because of the shape and overlapping of the cervical vertebrae. Therefore, to open up and demonstrate the cervical intervertebral foramina radiographically a 45 oblique position combined with a 15 degree cephalad angle of the x-ray beam is required.
Atlas (C1)
The first cervical vertebra, least resembles a typical vertibra. Anteriorly, there is no body but simply a thick arch of bone called the anterior arch. The anterior arch includes a small anterior tubercle.
The dens or odontoid process is part of the second cervical vertebra but a superior perspective of C1 shows its location and how it is held in place by the transverse atlantal ligament.
Rather than two laminae and a spinous process found in typical vertebrrae, C1 has a posterior arch that generally bears a small posterior tubercle at the midline.
Each of the left and right C1 superior articular processes presents a large depressed surface called a superior facet for articulation with the respective left and right occipital condyles of the skull. These articulations between C1 and the occipital condyles of the skull, are called occipitoatlantal joints. The transverse processes of C1 are smaller but still contain the transverse foramina distinctive of all cervical vertebrae.
The Articular pillars, the segments of bone between the superior and inferior articular processes, are called lateral masses for C1. Because the lateral masses of C1 support the weight of the head and assist in roation of the head, these portions are the most bulky and solid parts of C1.
Axis (C2)
The dens or odontoid process, the conical process that projects up from the superior surface of the body.
Relationship of C! and C2.
Normally, articulations between C2 and C1, the atlantoaxial joints, are symmetric. Accordingly, the relationship of the dens to C1 also must be perfectly symmetric.
Characteristics of Thoracic Vertebrae
T5, T6, T7, and T8 are considered typical thoracic vertebrae. The upper four thoracic vertebrae are smaller and share features of the cervical vertebrae. The lower four thoracic vertebrae are larger and share share characteristics of the lumbar vertebrae.
Rib articulations
all thoracic vertebrae have facets for articulation with ribs, L! and L2, do not show facets for rib articulations.
Costovertebral joints
Each thoracic vertebra has a full facet or two partial facets, called demifacets, on each side of the body. Each facet or combination of two demifacets accepts the head of a rib to form a costovertebral joint.
Vertebrae with two demifacets share articulations with the heads of ribs. For example, the head of the fourth rib straddles or articulates with demifacets on the vertebral bodies of both T3 and T4. The superior portion of the rib head articulates with the demifacet on the inferior margin of T3 and the inferior portion of the rib head articulates with the demifacet on the superior margin of T4.
T1 has a full facet and a demifacet on its inferior margin. T2 through T8 have demifacets on their upper and lower margins. T9 has only one demifacet on its upper margin. T10 through T12 have full facets. Rib 1 articulates with T1 only, rib 2 articulates with T1 and T2, and so forth. Ribs 11 and 12 articulate only with T11 and T12.
Costotransverse Joints
In addition to costovertebral joints, all of the first 10 thoracic vertebrae also have facets (one on each transverse process) that articulate with the tubercles of ribs 1 through 10. These articulations are termed costotransvere joints. T11 and T12 do not show facets at the ends of the transverse process for rib articulations. Thus, as the first 10 pairs of ribs arch posteriorly from the upper 10 vertebral bodies, the tubercle of each rib articulates with one transverse process to form a costotransverse joint. Ribs 11 and 12, articulate only at the costovertebral joints.
Lateral oblique perspective
The superior articular processes (facing primarily posteriorly) and the inferior articular processes (facing more anteriorly) are shown to connect the successive thoracic vertebrae to form the zygapophyseal joints.
On each side, between any thoracic vertebrae, are intervertebral foramina, which are defined on the superior and inferior margins by the pedicles.
thoracic zygapophyseal joints
The structure and angles of the facets of the inferior and superior articular processes making up the zyga joints differ markedly from those of the cervical and lumbar vertebrae. In the thoracic vertebrae, the zyga joints form an angle of 70 to 75 degree from the midsagittal plane.Therefore, for example, to open up and demonstrate the thoracic zyga jonts radiographically, a 70 to 75 oblique position with a perpendicular central ray is required.
thoracic intervertebral foramina
the openings of the intervertebral foramina on the thoracic vertebra are located at right angles, or 90 degree (lateral) to the midsagittal plane.
unique C1-C2 joint classifications
There are three joints involved between C!-C2 vertebrae. The first two joints are the right and left lateral antlantoaxial joints between the inferior articular surface of C1 (Atlas) and superior artilcular surface of C2 (axis). The third joint between C1-C2 is the medial atlantoaxial joint. This articulation is located between the dens of C2 an the anterior arch of C1 and is held in place by the transverse atlantal ligament.
AP Cervical Spine Image
Usually the first two or three thoracic vertebrae, as well as C7 to C3 are seen well on this position. T1 , can be identified by the attachment of the first pair of ribs.
Lateral Cervical Spine Image
The single most important radiograph clinically for a cervical spine series is a well-positioned lateral. All seven cervical vertebrae and the alignment with T1 should be demonstrated. 1) Dens are seen extending up through the anterior arch of C1. 2) Posterior arch of the atlas, C1, 3) Body of C3 D) zygapophyseal joint betweeen C4-C5 (best shown on a lateral projection for the cervical spine) E) Body of C7, F) Spinous process of C7, vertebra prominens.
Oblique Cervical Spine Image
The oblique position demonstrates the cervical intervertebral foramina. Spinal nerves to and from the cord are transmitted through these intervertebral foramina.
A) Posterior arch and tubercle of C1 B) Intervertebral foramen between C4 and C5 (count down from C!)
C) Pedicle of C) D) Body of C7.
Lateral Thoracic Spine
Intervertebral Foramina between T11 and T12 (this is best demonstrated on a lateral image of the T spine.)
Summary of Cervical Vertebrae
Three foramina each, more dominant articular pillars,
C1 (Atlas) No body but anterior and posterior arches, No spinous process, but posterior tubercle with bifid tip, lateral masses (articular pillars), superior facets for occipitoatlantal articulations.
C2, (Axis) Contains odontoid process (dens)
C2-C6 short spinous processes with bifid tips.
C7 called vertebra prominens because of its long spinous process.
Summary of Thoracic Vertebrae
All thoracic vertebrae 1) Contain facets for rib articulations (facets or demifacets) 2) T1-T10 Contain facets on transverse proceses for rib articulations. 3) T1-T10 contain facets on transverse processes for rib articulations. T1-T9 contain demifacets for rib articulation T10-T12 contain single facet for rib articulation.
Intervertebral foramina versus Zygapophyseal joints
Two anatomic areas of the spine that generally need to be demonstrated by the proper radiographs are the intervertebral foramina and zyga joints.
Cervical Spine Skeleton
The zyga joints visualize well in the lateral position.
The intervertebral foramina are visualized in a 45 degree oblique. It is important to know that the LPO position opens up the foramina on the right side and a 15 degree dephalad angle is needed. Therefore, on a posterior oblique cervical spine radiograph, the upside (side farthest from IR) is the side on which the intervertebral foramina are opened well. If this were taken in an anterior oblique position, with the foramina closest to the image receptor, the downside would be open and a 15 degree caudad angle would be required.
Cervical spine
The zyga joints are superimposed on the joints on the opposite side in the lateral position. It is important to remember that the zyga joints are located between the articular pillars of each vertebra.
The oblique cervical spine shows the circular intervertebral foramina opened. In each oblique radiograph, only one set of foramina are opened, whereas the ones on the opposite side are closed.
thoracc spine skeleton
The lateral position of the thoracic spine best shows the intervertebral foramina. A 70 degree oblique is necessary to open up the zyga joints on the t-spine. The posterior oblique position would show the upside, while the anterior would show the downside.
Topographic landmarks
The mastoid tip --C1 External Acoustic Meatus--EAM Gonion--C3 Thyroid Cartilage or Adam's Apple-- C5 Spinous Process--C7 Jugular notch --T2-T3 Sternal Angle T4-T5 Xiphoid Process T9-T10
Radiation
The thyroid dose of radiation can be reduced significantly by positioning the patient in an anterior oblique rather than a posterior oblique.
thoracic spine
is usually obtained with the use of an orthostatic (breathing) technique.to blur structures that overlie the thoracic vertebra. It involves taking shallowting breathes during the exposure time, with a low mA setting and 3 to 4 seconds exposure time. The thorax must not move.
Focal spot
The use of small focal spot can improve spatial resolution.
Scatter radiation
When the air gap technique is considered is during a lateral cervical. Placement of the IR far from the spine during lateral cervical radiography creates an air gap that reduces the amount of scatter radiation that reaches the IR This increased OID also contributes to greater magnification of the image, which accounts for an increase in SID to compensate.
Myelography
MRI and CT are replacing myelography as the modality of choice.
CT
used for evaluating spinal trauma such as fractures, subluxations, herniated disks, tumors, and arthropathies such as rheumatoid arthritis and osteoarthritis.
MRI
demonstrating soft tissue structures associated with the spine, such as the intervertebral disks and the spinal cord itself.
clay shoveler’s fracture
the fracture, which results from hyperflexion of the neck, results in avulsion fractures on the spinoous processes of C6-T1. The fracture is best demonstrated on a lateral cervical spine.
Compression fracture
frequently associated with osteoporosis, a compression fracture often involves collapse of a vertebral body, Seen best in a lateral position.
spondylitis
is inflammation of the vertebra.
spondylosis
characteristic of this condition is neck stiffness due to age-related degeneration of intervertebral disks.
kyphosis
abnormal or exaggerated convex thoracic curvature
AP Open Mouth Projection
Involving C!-C2, demonstrates odontoid and Jefferson fractures. Make sure that the patient keeps their tongue in the lower jaw to keep it from superimposing the atlas and axis. Optimal flexion/extension of the neck, indicated by superimposition of the lower margin of the upper incisors on the base of the skull. Neither the teeth nor the skull base base should superimpose the dens. If the teeth are superimposed on the upper dens, reposition by slight hyperextension of the neck or angel the CR slightly cephalic. If the base of the skull is superimposed on the upper dens, reposition by slight hyperflexion of the neck or angle the CR slightly caudal (the base of the skull and/or the supper incisors will be projected about 1 inch for every 5 degree of caudal angulation. No rotation indicated by equal distances from lateral masses and/or transverse processes of C1 to condyles of mandible, and by center alignment of spinouse process of C2
AP Axial Projection: Cervical Spine
Pathology involving the mid and lower C-Spine (C3-C7), SID 40” Adjust head so that a line from lower margin of upper incisors to the base of the skull (mastoid tips) is perpendicular to table and/or IR. Line from tip of mandible to base of skull should be parallel angled CR No rotation of thorax.
Angle CR 15 to 20 degrees
Direct CR to margin of thyroid cartilage to pass through C4
Cephalic angulation directs the beam between the overlapping cervical vertebral bodies to demonstrate the intervertebral disk spaces.
C3-T2 vertebral bodies; space between pedicles and intervertebral disk spaces clearly seen.
No rotation indicated by spinous processes and sternoclavicular joints (if visible) equidistant from the spinal column lateral border, the mandible and the base of the skull should superimpose the first two cervical vertebra
Anterior and Posterior Oblique Positions: Cervical Spine
Anterior Oblique (RAO-LAO are preferred because of reduced thyroid doses.Protract chin to prevent mandible from superimposing vertebrae. Elevating the chin too much will superimpose base of skull over C1.
Anterior Oblique–direct CR 15 degree caudad to C4
Posterior Oblique–direct CR 15 degree dephalad to C4
Anatomy demonstrated—Anterior: Oblique: intervertebral foramina and pedicles on the side of the patient closes to the IR
Posterior: Oblique: intervertebral foramina and pedicles on the side of the patient farthest from the IR.
Intervertebral disk spaces and intervertebral foramina of interest (C2 through C7) should be open and uniform in size and shape. The pedicles of interest should be demonstrated in full profile and the opposite, on-end pedicles demonstrated in full profile and the opposite, on end pedicles should be aligned along the anterior cervicle body. On end pedicles aligned along the anterior cervical boy and pedicles aligned at the midline of the cervical body and visualization of zygapopphyseal joints indicate over rotation.
Obscured intervertebral foramina and pedicles indicate under rotation. The mandibular rami should not superimpose the upper cervical vertebrae and the base of the skull should not superimpose C1.
Lateral Position: C-Spine
Spondylosis and osteoarthritis SID 60 to 72 inches, Direct CR horizontal to C4, full expiration (for maximum shoulder depression), long 72 inches SID compensates for increased OID and provides for greater spatial resolution.
Cervical vertebral boies, intervertebral joint spaces, articular pillars, spinous processes, and zyga joints.
C1 through C7-T1, intervertebral joint spaces are clearly seen. If upper margin of T1 is not demonstrated additional images such as the cervicothoracic lateral should be obtained. The rami of the mandible do not superimpose C! to C2. The right and left articular pillars and zyga joints should be superimposed for each vertebra. The bodies should be free of superimposition of the articular pillars and the spinous process seen in profile.
Cervicothoracic (swimmer’s) lateral position: Cervical spine (twining method for C5-T3) Direct CR to T1, which is approximately 1 inch above level of jugular notch anteriorly and at the level of vertebra prominens posteriorly.
Vertebral bodies and intervertebral disk spaces of C5-T3 are shown. The humeral head and arm farthest from the IR are magnified and appear distal to T4 or T5.
Minimal vertebral rotation indicated by superimposition of cervical zyga joints and articular pillars, and posterior ribs. The humeral heads should be separated vertically.
Okay
Lateral Positions–Hyperflexion and Hyperextension: Cervical Spine
SID C1-C7, No rotation of head is indicated by superimposition of mandibular rami, for hyperflexion: spinous processes should be well separated. For hyperextension: spinous process shouldd be in close proximity. Direct CR to C4
AP or Pa projection for C1-C2 (dens): C-spine (fuchs method (AP0 or Judd method (PA)
SID 40O
Elevate Chin as needed to bring MML (mentomeatal line)
Dens should be centered within the foramen magnum. No rotation indicated by the symmetric appearance of the mandible arched over the foramen magnum. Correct extension of head and neck indicated by the tip of the mandible clearing the superior portion of the dens and foramen magnum.
AP Projection: T-spine
The anode heel effect will create more uniform density throughout the thoracic spine. Place patient so the more intense aspect of the beam (cathode side) is over the thoracolumbar region.
flex knees and hips to reduce thoracic curvature.
direct CR to T7
Anatomy demonstrated: Thoracic vertebral bodies, intervertebral joint spaces, spinous and transverse processes, posterior ribs, and costovertebral articulations.
The spinal column from C7 to L! centered to the midline of the IR, No rotation indicated by sternoclavicular joints equidistant from the spine.
Lateral Position: Thoracic Spine
Pathology involving the thoracic spine, such as compression fractures, subluxation, or kyphosis
Direct CR to T7
Anatomy demonstrated: Thoracic vertebral bodies, intervertebral joint spaces, and intervertebral foramina, T1 to T3 will not be visualized, Obtain a lateral image using a cervicothoracic (swimmer’s) lateral if the upper thoracic vertebrae are of special interest.
Intervertebral disk spaces should be open.
No rotation indicated by superimposition of posterior aspects of vertebral bodies
Oblique Position —Anterior or Posterior Oblique: T-Spine
Pathology involving the Zyga jonts.
Rotate the body 20 degrees from true lateral to create a 70 degrees oblique from plane of table. Ensure equal reotation of shoulers and pelvis.
CR to T7
Zyga jonts: Anterior Oblique (RAO and LAO) demonstrate the downside zyga joints and posterior oblqiue positions (RPO and LPO) demonstrate the upside.
Hip
is proximal
List the number of bones found in each division in the adult vertebral column.
Cervical 7 Thoracic 12 Lumbar 5 Sacrum 1 Coccyx 1 Total 26
List the two primary or posterior convex curves seen in the vertebral column.
Thoracic and Sacral
Indicate which two portions of the vertebral column are classified as secondary or compensatory curves.
Cervical and lumber
Which are the convex curves
Thoracic and Sacrum
Which are the concave curves
Cervical and Lumbar
Which are the secondary curves
Cervical and lumbar
Which are the primary Curve
Thoracic and Sacrum
Develops as a child learns to hold head erect
Cervical
An abnormal or exaggerated, “sway back” lumbar curvature is called
lordosis
An abnormal lateral curvature seen in the thoracolumbar spine is callled
scoliosis
The two main parts of a typical vertebra are the
body and the vertebral arch
The ? are two bony aspects of the vertebral arch that extend postriorly from each pedicle to join at the midline.
Lamina
The ? foramina are created by two small notches on the superior and inferior aspects of the pedicles.
Intervertebral
The opening, or passageway, for the spinal cord is the
Vertebral spinal canal
The spinal cord begins with the ? of the brain and extends down to the ? vertebra, where it tapers and ends. This tapered ending is called the ?
Medulla Oblongata
lower border of L1
conus medullaris
Which structures pass through the intervertebral foramina?
Spinal nerves and blood vessels
Which of the following is found between the superior and inferior articular processes?
Zyga joints
Only T1, T11, and T12 have full facets for. articulation with ribs
True
The Zyga joints of all cervical vertebrae are visualized only in a true lateral position.
true
List the outer and inner aspect
of the intervertebral disk
Outer Aspect–Annulus Fibrosus
Inner Aspect–Nucleaus Pulposus
The condition involving a “slipped disk” is correctly referred to as
Herniated nucleus pulposus
List the alternative names for the following cervical vertebrae
C!–Atlas
C2-Axis
C7-Vertebra Prominens
List three features that make the cervical vertebrae unique
Transverse foramina
bifid spinous process
overlapping vertebral bodies
A short column of bone found between the superior and articular processes in a typical cervical vertebra s alled
articular pillar
What is the term for the same structure, identified in the previous question, for the C1 vertebra.
Lateral mass
