2.6: Lab Exercise 7- The Skeletal System—Bones and Bone Markings

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Lab Summary: In this lab, you will learn how to identify the bones of the skeleton, determine if the bones are left or right, and identify certain bone markings. “Bone markings” is a term used to describe all of the holes, ridges, canals, bumps, and lines that exist on bones. Generally, these markings are passageways for blood vessels and nerves, attachment points for muscles, or specialized shapes on bones where they meet each other at joints. In clinical applications, the names of bones or markings are often used to describe blood vessels or other important structures, superficial areas of the body, and are used as landmarks for

palpation. Here are some examples:

A radial pulse is taken at the radial artery, which is named for the radius bone along which it lies.
The calcaneal tendon joins the gastrocnemius muscle to the calcaneus bone of the foot; hence, the tendon is named after its bone.
Mastoiditis is an inflammation of cells in the mastoid process of the temporal bone. Knowing where the mastoid process is would help you pinpoint the area of inflammation and patient pain.
The acromion process of the scapula is a landmark used when learning to give intramuscular injections in the deltoid muscle.

In future labs in this course and others, you will learn about origins and insertions for muscles; these origins and insertions are usually specific bones and/or their markings. So, the better you know the bones and markings, the easier it will be to learn origins and insertions for muscles.

Your objectives for this lab are:

Identify the major divisions of the skeleton, axial vs appendicular, and which bones belong to each group
Provide examples of each type of bone classification by shape
Identify disarticulated bones as left or right. Be able to describe how you made this determination
Identify the 206 bones and selected bone markings on articulated skeletons (or portions of the skeleton) and disarticulated bones. The list below specifies the axial bones you need to know and the specific bone markings required for each bone. Activity 2 focuses on the Axial Skeleton; Activity 3 focuses on appendicular bones. Do note that all bones have markings, but you need to study the following:

Cranial and Facial Bones of the Skull

Frontal bone
Parietal bones
Occipital bone, and Foramen magnum, Occipital condyles, External occipital protuberance (EOP)
Temporal bone, and Mastoid process, Styloid process, External auditory canal /external acoustic meatus, Jugular foramen, Carotid canal, Mandibular fossa
Ethmoid bone, and Perpendicular plate, Nasal conchae, Cribriform plate and olfactory foramina
Sphenoid bone, and Sella turcica, Optic foramina/canals
Nasal bones
Maxilla(e)
Lacrimal bones
Zygomatic bones
Palatine bones
Mandible, and Mental foramen, Mandibular condyles Sutures (these are joints between bones, but not bones themselves)
Coronal suture (also known as frontal suture)
Sagittal suture
Squamous suture
Lambdoidal suture

Vertebral column (identify vertebrae by name and number if articulated; identify vertebra from different regions by their characteristic features if articulated or disarticulated)

Body/centrum
Vertebral arch and the specific areas called pedicles, lamina and spinous process
Transverse processes
Transverse foramen (what structures pass through here?)
Vertebral foramen (what structure passes through here?)
Intervertebral foramina (what structures pass through here?)
Cervical vertebrae (C1-C7), you should also be able to identify C1 and C2 as disarticulated bones
- Atlas aka C1
- Axis aka C2, and its Dens/Odontoid process
Thoracic vertebrae (T1-T12), and its Articulating facets (for ribs)
Lumbar vertebrae (L1-L5)
Sacrum
Coccyx
Intervertebral discs (an important structural component of the spine, but not a bone)

The Thorax

Sternum, and Manubrium, Jugular notch, Body, Xyphoid process
Ribs (be able to identify them by number if they are articulated)
- Costal cartilages (important structural component of the thorax, but not a bone)
- Identify ribs as True, False and/or Floating ribs

Upper Extremity

Clavicle, and Sternal end, Acromial end
Scapula, and Spine, Acromion process, Coracoid process, Glenoid fossa/cavity, supraspinous fossa, infraspinous fossa, subscapular fossa
Humerus, and Head, Deltoid tuberosity, Trochlea, Capitulum, Olecranon fossa
Ulna, and Olecranon process, Styloid process (medial)
Radius, and Styloid process (lateral), Head
Carpals—scaphoid, lunate, triquetral, pisiform, trapezium, trapezoid, capitate, hamate
Metacarpals (#1-5)
Phalanges (#1-5; proximal, intermediate, distal)

Lower Extremity

Ilium, Ischium, Pubis/pubic bone, and these markings
- Anterior superior iliac spine (ASIS)
- Iliac crest
- Greater sciatic notch
- Obturator foramen
- Acetabulum
- Pubic symphysis (not a bone but an important structural feature of the pelvis)
- Ischial tuberosity
Femur, and Head, Neck, Greater trochanter, Linea aspera, Medial and lateral condyles
Tibia, and Medial and lateral condyles, Medial malleolus, Tibial tuberosity
Fibula, and Lateral malleolus
Patella
Tarsals—talus, calcaneus, cuboid, navicular, medial cuneiform, intermediate cuneiform, lateral cuneiform
Metatarsals (#1-5)
Phalanges (#1-5; proximal, intermediate, distal)

Activity 7.1: Understanding Bone Markings

Bones are highly architectured and complex organs. The surface features of bones vary considerably, depending on the function and location in the body. There are three general classes of bone markings: (1) articulations, (2) projections, and (3) holes. As the name implies, an articulation, or joint, is where two bone surfaces come together. These surfaces tend to conform to one another, such as one being rounded and the other cupped, to facilitate the function of the articulation. A projection is an area of a bone that projects above the surface of the bone. These are the attachment points for tendons and ligaments. In general, their size and shape is an indication of the forces exerted through the attachment to the bone. A hole is an opening or groove in the bone that allows blood vessels and nerves to enter the bone. As with the other markings, their size and shape reflect the size of the vessels and nerves that penetrate the bone at these points. Table 7.1 lists and describes the major bone features.

Review the information in Table 7.1 before moving on to the next activity.

Table \(\PageIndex{1}\): **General Types Bone Features**
Marking	Description	Example
Head	Prominent rounded surface	Head of femur
Facet	Flat surface	Articular facets of vertebrae
Condyle	Rounded surface	Occipital condyle
Process	Projection from the bone	Spinous process of vertebrae
Spine	Short, sharp projection	Transverse process of vertebrae
Tubercle	Small, rounded process	Ischial spine
Tuberosity	Large, rough surface of a bone	Tubercle of humerus
Line	Smaller elevated ridge of bone	Temporal lines of parietal bone
Crest	Larger elevated ridge of bone	Iliac crest
Fossa	Larger pit in a bone	Mandibular fossa
Fovea	Smaller pit in a bone	Fovea capitis of femur
Sulcus	Groove	Sigmoid sulcus of temporal bone
Canal	Small passage in bone	Auditory canal
Fissure	Slit through bone	Inferior orbital fissure
Foramen	Hole through bone	Foramen magnum
Meatus	Opening into a canal	External auditory meatus
Sinus	Open space in bone	Nasal sinus

Activity 7.2: Bones and Bone Markings of the Axial Skeleton

Procedure for Activity 7.2:

Use the information and figures that follow to identify the bones and required bone markings for the axial skeleton. These are listed in the objectives at the beginning of this lab.

The Skull

The cranium (skull) is the skeletal structure of the head that protects the brain and supports the face. It is subdivided into the brain case and facial bones (Figure \(\PageIndex{1}\)). The rounded brain case surrounds and protects the brain and houses the middle and inner ear structures. The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws.
In the adult, the skull consists of 22 individual bones, 21 of which are virtually immobile and united into a single unit. The 22nd bone is the mandible (lower jaw), which is the only truly moveable bone of the skull. The brain case consists of eight bones including the paired parietal and temporal bones, plus the unpaired frontal, occipital, sphenoid, and ethmoid bones; the face is composed of 14 bones (Figure \(\PageIndex{2}\)-Figure \(\PageIndex{7}\)).

Bones of the Brain Case (Cranium)

The brain case (cranium) contains and protects the brain. The interior space is called the cranial cavity. The bones that form the top and sides of the brain case are usually referred to as the “flat” bones of the skull. The floor of the brain case is referred to as the base of the skull. This is a complex area that varies in depth and has numerous openings for the passage of cranial nerves, blood vessels, and the spinal cord.

The frontal bone (Figure \(\PageIndex{2}\)) is the single bone that forms the forehead supraorbital margin of the orbit, forming rounded ridges under the eyebrows. It extends into the eye socket to form the roof of the orbit below and the floor of the anterior cranial cavity above. The paired parietal bones forms most of the upper lateral side of the skull. The occipital bone is the single bone that forms the posterior skull and posterior base of the cranial cavity; it contains the large opening of the foramen magnum, which allows for passage of the spinal cord as it exits the skull. On either side of the foramen magnum is an oval-shaped occipital condyle, which form joints with the first cervical vertebra and thus support the skull on top of the vertebral column. The paired temporal bones forms the lower lateral side of the skull.

The sphenoid bone is a single, complex bone of the central skull (Figure \(\PageIndex{2}\), Figure \(\PageIndex{3}\), Figure \(\PageIndex{5}\), Figure \(\PageIndex{7}\)). It serves as a “keystone” bone, because it joins with almost every other bone of the skull. The sphenoid forms much of the base of the central skull (Figure \(\PageIndex{5}\)) and extends laterally to contribute to the sides of the skull (see Figure \(\PageIndex{2}\), Figure \(\PageIndex{3}\)). Among its many markings is the sella turcica (“Turkish saddle”), located in between the lesser wings, which houses the pea-sized pituitary gland. The sphenoid bone also forms a portion of the orbit. At the posterior apex of the orbit is the opening of the optic canal, which allows for passage of the optic nerve from the eyeball to the brain.

The ethmoid bone (Figure \(\PageIndex{2}\), Figure \(\PageIndex{3}\), Figure \(\PageIndex{5}\), Figure \(\PageIndex{6}\)) is a single, midline bone that forms the roof and lateral walls of the upper nasal cavity, the upper portion of the nasal septum, and contributes to the medial wall of the orbit. Within the nasal cavity, the perpendicular plate of the ethmoid bone forms the upper portion of the nasal septum. The bone also contains the crista galli and cribriform plates. The crista galli (“rooster’s comb”) is a small upward bony projection located at the midline, which functions as an anterior attachment point for one of the covering layers (dura mater) of the brain. To either side of the crista galli is the cribriform plate, a small, flattened area with numerous small openings termed olfactory foramina. Small nerve branches from the olfactory areas of the nasal cavity pass through these openings to enter the brain.

Sutures of the Skull

A suture is an immobile fibrous joint between adjacent bones of the skull. The narrow gap between the bones is filled with dense, fibrous connective tissue that unites the bones. The long sutures located between the bones of the brain case are not straight, but instead follow irregular, tightly twisting paths. These twisting lines serve to tightly interlock the adjacent bones, thus adding strength to the skull for brain protection (Figure \(\PageIndex{2}\), Figure \(\PageIndex{4}\)).

The coronal suture, also known as the frontal suture, runs from side to side across the skull, within the coronal plane of section; it joins the frontal bone to the right and left parietal bones.

The sagittal suture extends posteriorly from the coronal suture, running along the midline at the top of the skull in the sagittal plane of section to unite the right and left parietal bones. On the posterior skull, the sagittal suture terminates by joining the lambdoid suture.

The lambdoid(al) suture extends downward and laterally to either side away from its junction with the sagittal suture. The lambdoid suture joins the occipital bone to the right and left parietal and temporal bones. This suture is named for its upside-down "V" shape, which resembles the capital letter version of the Greek letter lambda (Λ).

The squamous(al) suture is located on the lateral skull. It unites the sphenoid, frontal, squamous portion of the temporal bone, and the parietal bone.

For more information on the functions and features of specific bone markings for your lab, read Section 7.2 in the OpenStax A&P textbook here: https://openstax.org/books/anatomy-and-physiology/pages/7-2-the-skull

Figure \(\PageIndex{2}\): Lateral View of Skull.

Figure \(\PageIndex{3}\): Anterior View of Skull.

Figure \(\PageIndex{4}\): Posterior View of Skull.

Figure \(\PageIndex{5}\): External and Internal Views of the Base of the Skull.

Figure \(\PageIndex{6}\): Anterior view of ethmoid bone.

Figure \(\PageIndex{7}\): Sphenoid bone.

Facial Bones

The anterior skull consists of the facial bones and provides the bony support for the eyes and structures of the face, as well as attachment points for muscles of facial expression and speaking. The facial bones of the skull form the upper and lower jaws, the nose, nasal cavity and nasal septum, and the orbit. The facial bones include 14 bones: six paired bones and two unpaired bones (Figure \(\PageIndex{2}\), Figure \(\PageIndex{3}\), Figure \(\PageIndex{8}\), Figure \(\PageIndex{9}\), Figure \(\PageIndex{10}\)). Although classified with the brain-case bones, the ethmoid bone also contributes to the nasal cavity and orbit and the sphenoid and frontal bones make up part of the orbit.

The maxilla, or maxillary bone, (Figure \(\PageIndex{10}\)), (plural = maxillae), is one of a pair that together form the upper jaw, much of the hard palate, the medial floor of the orbit, and the lateral base of the nose. On the inferior skull, the maxillary bone can be seen joining together at the midline to form the anterior three- quarters of the hard palate that forms the roof of the mouth and floor of the nasal cavity, separating the oral and nasal cavities.

The paired palatine bones are irregularly shaped bones that contribute small areas to the lateral walls of the nasal cavity and the medial wall of each orbit (Figure \(\PageIndex{5}\)). The plates from the right and left palatine bones join together at the midline to form the posterior quarter of the hard palate. Thus, the palatine bones are best seen in an inferior view of the skull and hard palate.

The paired zygomatic bones, “the cheekbone”, form much of the lateral wall of the orbit and the inferolateral margins of the anterior orbital opening (Figure \(\PageIndex{3}\), Figure \(\PageIndex{5}\)). The short temporal process of the zygomatic bone projects posteriorly and joins the zygomatic process of the temporal bone; together these two structures form the zygomatic arch. One of the major muscles that pull the mandible upward during biting and chewing arises from the zygomatic arch.

The two small nasal bones (Figure \(\PageIndex{3}\)) articulate with each other to form the bony bridge of the nose. They also support the cartilages that form the lateral walls of the nose. These are the bones that are damaged when the nose is broken.

Each lacrimal bone is a small, rectangular bone that forms the anterior, medial wall of the orbit (Figure \(\PageIndex{2}\), Figure \(\PageIndex{3}\)). The lacrimal fluid (tears of the eye) drains at the medial corner of the eye, which extends downward to open into the nasal cavity. In the nasal cavity, the lacrimal fluid normally drains posteriorly, but with an increased flow of tears due to crying or eye irritation, some fluid will also drain anteriorly, thus causing a runny nose.

The unpaired vomer is triangular-shaped bone that forms the posteroinferior part of the nasal septum (Figure \(\PageIndex{3}\)). In an anterior view of the skull, the vomer can be seen articulating to the perpendicular plate of the ethmoid bone, which forms the superior portion of the nasal septum. The vomer can also be seen in an inferior view of the skull.

The mandible (Figure \(\PageIndex{10}\)) forms the lower jaw and is the only moveable bone of the skull. At the time of birth, the mandible consists of paired right and left bones, but these fuse together during the first year to form the single U-shaped mandible of the adult skull. Each side of the mandible consists of a horizontal body; posteriorly, there is a vertically oriented ramus of the mandible (ramus = “branch”). The ramus contains two bony projections: coronoid process (anterior) and the mandibular condyle (posterior). The flattened coronoid process provides attachment for one of the biting muscles. The oval-shaped mandibular condyle, also known as the condylar process of the mandible, articulates (joins) with the mandibular fossa and articular tubercle of the temporal bone. Together these articulations form the temporomandibular joint (TMJ), which allows for opening and closing of the mouth.

The hyoid bone (Figure \(\PageIndex{11}\)) is the only bone that does not articulate with another bone. Instead, its importance lies in the fact that it is an anchor point for many muscles associated with speaking. You can palpate this bone easily: put your index fingers on the underside of the mandible’s body, move your fingers slightly medial, then very gently push your fingers upward while moving your tongue. Some say this bone resembles Halloween vampire teeth when disarticulated.

For more information on the functions and features of specific bone markings for your lab, read Section 7.3 in the OpenStax A&P textbook here: https://openstax.org/books/anatomy-and-physiology/pages/7-2-the-skull

Figure \(\PageIndex{8}\): **Bones of the Orbit.** The orbit is the bony socket that houses the eyeball and contains the muscles that move the eyeball and the upper eyelid.

Figure \(\PageIndex{11}\): The Hyoid Bone

The Fetal Skull

As the cranial bones grow in the fetal skull, they remain separated from each other by large areas of dense connective tissue, called fontanelles (Figure \(\PageIndex{12}\)). The fontanelles are the “soft spots” on an infant’s head and are important during birth because these areas allow the skull to change shape as it squeezes through the birth canal. After birth, the fontanelles allow for continued growth and expansion of the skull as the brain enlarges. The most familiar and largest of these is the anterior fontanelle, at the junction of the frontal and parietal bones. Additionally, there are posterior, mastoid, and sphenoid fontanelles, which decrease in size and disappear by age 2. However, the skull bones remain separated from each other at the sutures. The connective tissue of the sutures allows for continued growth of the skull bones as the brain enlarges during childhood growth.

The second mechanism for bone development in the skull produces the facial bones and floor of the brain case. A hyaline cartilage model of the future bone is produced; as this cartilage model grows, it is gradually converted into bone through endochondral ossification. This is a slow process, which is not completed until the skull achieves its full adult size.

At birth, the cranial case and orbits of the skull are disproportionally large compared to the bones of the jaws and lower face. This reflects the relative underdevelopment of the maxilla and mandible, which lack teeth, and the small sizes of the paranasal sinuses and nasal cavity. During early childhood, the mastoid processes enlarge, the two halves of the mandible and frontal bone fuse together to form single bones, and the paranasal sinuses enlarge. The jaws also expand as the teeth begin to appear. These changes contribute to the rapid growth and enlargement of the face during childhood.

Figure \(\PageIndex{12}\): Bones and fontanels of the fetal skull.

The Vertebral Column

Regions of the Vertebral Column

The vertebral column is subdivided into five regions (Figure \(\PageIndex{13}\)), with the vertebrae (singular = vertebra) in each area named for that region and numbered in descending order. In the neck, there are usually seven cervical vertebrae, each designated with the letter “C” followed by its number. Superiorly, the C1 vertebra (the atlas) articulates with the occipital condyles of the skull. Inferiorly, C1 articulates with the C2 vertebra (the axis); the remaining cervicals are numbered 3—7. Inferiorly are the 12 thoracic vertebrae, designated T1– T12. The lower back contains the L1–L5 lumbar vertebrae. The single sacrum, which is also part of the pelvis, is formed by the fusion of five sacral vertebrae. Similarly, the coccyx, commonly known as “tailbone”, results from the fusion of three to five coccygeal vertebrae. However, the sacral and coccygeal fusions do not start until age 20 and are not completed until middle age.

General Structure of a Vertebra

Within the different regions of the vertebral column, vertebrae vary in size and shape, but they all follow a similar structural pattern. A typical vertebra consists of a body, a vertebral arch, and seven processes (Figure \(\PageIndex{14}\)).

Body: the anterior portion that supports the body weigh; progressively increase in size and thickness going down the vertebral column; separate but strongly united by an intervertebral disc
Vertebral arch: the posterior portion of each vertebra; consists of the two pedicles two lamina
- Pedicle: forms one of the lateral sides of the vertebral arch; anchored to the posterior side of the vertebral body
- Lamina: forms part of the posterior roof of the vertebral arch
Vertebral foramen: large opening between the vertebral arch and the body; serves as a passageway for the spinal cord
Seven processes: arise from the vertebral arch
- Transverse process (2) project laterally from the junction between the pedicle and lamina; muscle attachment point
- Spinous process (1) projects posteriorly at the midline of the vertebra (except C1, which has a posterior tubercle instead); easily palpated (felt) as a series of bumps just under the skin down the middle of the back; muscle attachment point
- Superior articular facets/processes (2) and Inferior articular facets/processes (2)
  - Superior facets face upward, and inferior facets face downward on each side of a vertebrae. Paired superior articular processes of one vertebra articulate with the corresponding pair from the next lower vertebra, forming slightly moveable joints between the adjacent vertebrae. Shape and orientation of the articular facets vary in different regions of the vertebral column and play a major role in determining the type and range of motion available in each region.

Figure \(\PageIndex{14}\): Parts of a typical vertebra

Cervical Vertebrae

Typical cervical vertebrae (Figure \(\PageIndex{15}\)), such as C4 or C5, have several characteristic features that differentiate them from thoracic or lumbar vertebrae. The following characteristics are typical of most cervical vertebrae (except C1 and C2):

small body, reflecting the fact that they carry the least amount of body weight
bifid (Y-shaped) spinous process
- these are short for C3–C6, but much longer on C7 • curved (U-shaped) transverse processes
- contain transverse foramen (in the transverse processes) to allow for passage of the cervical spinal nerves and the basilar arteries that supply collateral blood circulation to the brain
superior and inferior articular processes of the cervical vertebrae are flattened and largely face superiorly or inferiorly, respectively

C1 (atlas) and C2 (axis) are further modified, giving each a distinctive appearance, which makes it possible to identify them disarticulated from the rest of the vertebra. You will need to do this. C1 is also called the atlas because it supports the skull (“the heavens”). In Greek mythology, Atlas was the god who supported the heavens on his shoulders. C2 is also called the axis because the dens of C2 serves as an axis of rotation for the head.

Key characteristics of C1:

ring-shaped
no body or spinous process
transverse processes are longer and extend more laterally than any other cervical vertebrae
superior articular processes face upward and are deeply curved for articulation with the occipital condyles of the base of the skull
inferior articular processes are flat and face downward to join with the superior articular processes of C2

Key characteristics of C2:

bony projection called the dens or odontoid process (from the Greek for “tooth”) extends upward from the vertebral body and fits inside the atlas above, where it is held in place by a ligament

Figure \(\PageIndex{15}\): Cervical Vertebrae.

Thoracic Vertebrae

The bodies of the thoracic vertebrae (Figure \(\PageIndex{16}\)) are larger than those of cervical vertebrae. Thoracic vertebra close to the cervical and lumbar regions display “muted” features that seem to blend cervical and thoracic or cervical and lumbar features, respectively.

The following characteristics are typical of midthoracic vertebra:

medium-sized, heart-shaped body
spinous process is long and has a pronounced downward angle that causes it to overlap the next inferior vertebra
superior articular facets/processes face anteriorly
inferior articular facets/processes face posteriorly
additional articulation sites for the ribs, called articular facets and costal facets, are present on the lateral sides of the vertebral body and transverse processes

Figure \(\PageIndex{16}\): Thoracic Vertebrae.

Lumbar Vertebrae

Lumbar vertebrae (Figure \(\PageIndex{17}\)) carry the greatest amount of body weight and are thus characterized by the large size and thickness of the vertebral body.

The following characteristics are typical of lumbar vertebrae:

large, thick vertebral body
short transverse processes
short, blunt spinous process that projects posteriorly
large articular processes (as compared to all other vertebrae)
superior process facing posteriorly
inferior facing anteriorly

Figure \(\PageIndex{17}\): Lumbar Vertebra.

Sacrum and Coccyx

The sacrum (Figure \(\PageIndex{18}\)) is a triangular-shaped bone that is thick and wide across its superior base where it is weight bearing; it, then, tapers down to an inferior, non-weight bearing apex. It is formed by the fusion of five sacral vertebrae; this process begins after the age of 20. On the anterior surface of the older adult sacrum, the lines of vertebral fusion are seen as four transverse ridges. On the posterior surface, the remnant of the fused spinous processes and transverse processes of the sacral vertebrae are seen as vertical, bumpy ridges.

The coccyx (Figure \(\PageIndex{18}\)), commonly known as the “tailbone”, is derived from the fusion of three to five very small coccygeal vertebrae. It articulates with the inferior tip of the sacrum. It is not weight bearing in the standing position but may receive some body weight when sitting.

Figure \(\PageIndex{18}\): Sacrum and Coccyx.

The Thoracic Cage

The thoracic cage (rib cage) protects the heart, lungs, and other vital organs. The thoracic cage consists of the sternum and the 12 pairs of ribs with their costal cartilages (Figure \(\PageIndex{19}\)). The ribs are anchored posteriorly to the 12 thoracic vertebrae (T1–T12).

The sternum (Figure \(\PageIndex{19}\)) is the elongated bony structure that anchors the anterior thoracic cage. It consists of three parts: the manubrium, body, and xiphoid process. The body contains six costal notches on each side where ribs 2-7 articulate with the second rib attaching near the sternal angle (the connection between the manubrium and the body). Since the first rib is hidden behind the clavicle, the second rib is the highest rib that can be identified by palpation. Thus, the second rib and the sternal angle are important landmarks for the identifying and counting the lower ribs. The inferior tip of the sternum, known as the xiphoid process, serves as an attachment site for several muscles. This small structure is cartilaginous early in life, but gradually becomes ossified starting during middle age. It is the structural upon which we taught not to do compressions during CPR.

Each rib is a curved, flattened bone that contributes to the wall of the thorax. The 12 pairs of ribs, numbered 1—12, articulate posteriorly with the T1–T12 thoracic vertebrae (Figure \(\PageIndex{19}\)). The bony ribs do not extend anteriorly completely around to the sternum. Instead, the ends of each rib are costal cartilages (composed of hyaline cartilage), which can extend for several inches. Ribs 1–7 are classified as true ribs (vertebrosternal ribs) because the cartilage from each of these ribs attaches directly to the sternum. Ribs 8–12 are called false ribs (vertebrochondral ribs) because the cartilages from these ribs do not attach directly to the sternum. For ribs 8–10, the cartilages are attached to the cartilage of the next higher rib: the costal cartilage of rib 10 attaches to the cartilage of rib 9, et al). The last two ribs (11–12) are called floating ribs (vertebral ribs) because they are short ribs that do not attach to the sternum at all. Instead, their small costal cartilages terminate within the musculature of the lateral abdominal wall.

For more information on the functions and features of specific bone markings for your lab, read Section 7.4 in the OpenStax A&P textbook here: https://openstax.org/books/anatomy-and-physiology/pages/7-4-the-thoracic-cage

Figure \(\PageIndex{19}\): Thoracic cage

Activity 7.3: Bones and Bone Markings of the Upper Appendicular Skeleton

Procedure for Activity 7.3:

Use the information and figures that follow to identify the bones and required bone markings for the upper appendicular skeleton. These are listed in the objectives at the beginning of this lab.
Similar to the lower limb, the bones of your upper limb provide a strong internal supporting structure. However, because of our upright stance, different functional demands are placed on the upper and lower limbs which translates to some key structural differences. This activity focuses on the bones of the upper limb, from the shoulder to the hand.

The Pectoral Girdle & Upper Limb

The scapula and clavicle (Figure \(\PageIndex{20}\)) attach each upper limb to the axial skeleton forming the pectoral girdle (shoulder girdle). The right and left pectoral girdles are not joined to each other, allowing each to operate independently. In addition, the clavicle of each pectoral girdle is anchored to the axial skeleton by a single, highly mobile joint. This allows for the extensive range of motion at the shoulder joint. The upper limb is divided into three regions: the arm (between the shoulder and elbow joints), the forearm (between the elbow and wrist joints), and the hand (distal to the wrist). The humerus is the single bone of the upper arm, and the ulna (medially) and the radius (laterally) are the paired bones of the forearm. The base of the hand contains eight bones, each called a carpal bone, and the palm of the hand is formed by five bones, each called a metacarpal bone. The fingers and thumb are called the phalanges of the hand.

The scapula, located on the posterior side of the shoulder, plays an important role in anchoring the upper limb to the body. It is surrounded by muscles on both its anterior (deep) and posterior (superficial) sides, and thus does not articulate with the ribs of the thoracic cage. The scapula has several important landmarks (Figure \(\PageIndex{22}\)) that serve as attachment points for muscles of the rotator cuff and those involved in shoulder, arm, and chest movements. One of the many notable bone marking is the acromion process because it is an important clinical landmark for intramuscular injections into the deltoid muscle.

The clavicle (Figure \(\PageIndex{21}\)) is the most frequently broken bone in the human body! Consider its position. It is attached on its medial end to the sternum of the thoracic cage, which is part of the axial skeleton. The lateral end of the clavicle articulates with the scapula just above the shoulder joint. You can easily palpate, or feel with your fingers, the entire length of your clavicle. The acromioclavicular joint (formed where the acromion process of the scapula meets the lateral end of the clavicle) transmits forces from the upper limb to the clavicle. The ligaments around this joint are relatively weak. Following a strong blow to the lateral shoulder, such as when a hockey player is checked into the boards, a complete dislocation of the acromio-clavicular joint can result. In this case, the acromion is thrust under the lateral/acromial end of the clavicle, resulting in ruptures of both the acromioclavicular and coracoclavicular ligaments. This dislocation injury of the acromioclavicular joint is known as a “shoulder separation” and is common in contact sports such as hockey, football, or martial arts.

Figure \(\PageIndex{20}\): The Pectoral Girdle

Figure \(\PageIndex{21}\): **The Clavicle** Top view shows the anterior side of the left clavicle; Bottom view shows the posterior side of the left clavicle (Photo credit: Julie Robinson, CC-BY)

The humerus is the single bone of the upper arm (Figure \(\PageIndex{23}\), Figure \(\PageIndex{24}\)). At its proximal end is the head of the humerus, which faces medially and articulates with the glenoid cavity of the scapula to form the glenohumeral (shoulder) joint. The distal end of the humerus has two articulation areas—the trochlea on the medial side and the capitulum on the lateral side, which join the ulna and radius bones of the forearm to form the elbow joint. On the posterior humerus is the olecranon fossa, a larger depression that receives the olecranon process of the ulna when the forearm is fully extended.

The ulna is the medial bone of the forearm. It runs parallel to the radius, which is the lateral bone of the forearm (Figure \(\PageIndex{25}\)). The posterior and superior portions of the proximal ulna make up the olecranon process, which forms the bony tip of the elbow. The lateral side of the diaphysis forms a ridge called the interosseous border of the ulna, which is the line the dense connective tissue (the interosseous membrane) that connects the ulna and radius bones. Projecting from the posterior side of the ulnar head is the styloid process of the ulna, a short bony projection, which serves as an attachment point for a connective tissue structure that connects the distal ends of the ulna and radius.

The radius runs parallel to the ulna, on the lateral side of the forearm (Figure \(\PageIndex{25}\)). The head of the radius is a disc-shaped structure that forms the proximal end. The smooth, outer margin of the head articulates with the radial notch of the ulna at the proximal radioulnar joint. The shaft of the radius is slightly curved and has a small ridge along its medial side, which forms the interosseous border of the radius, which, like the similar border of the ulna, is the line of attachment for the interosseous membrane that unites the two forearm bones. The lateral end of the radius has a pointed projection called the styloid process of the radius. This provides attachment for ligaments that support the lateral side of the wrist joint. Compared to the styloid process of the ulna, the styloid process of the radius projects more distally, thereby limiting the range of movement for lateral deviations of the hand at the wrist joint.

The wrist and base of the hand are formed by a series of eight small carpal bones (see Figure \(\PageIndex{26}\)). formed as follows: a proximal row of four carpal bones and a distal row of four carpal bones. In the proximal row, the bones are joined to each other by ligaments; running from the lateral (thumb) side to the medial side, they are the scaphoid (“boat-shaped”), lunate (“moon-shaped”), triquetrum/triquetral bone (“three-cornered”), and pisiform (“pea-shaped”) bones. Although the pisiform may appear fused to the triquetrum/triquetral bone, it is not! The distal bones (lateral to medial) are the trapezium (“table”), trapezoid (“resembles a table”), capitate (“head-shaped”), and hamate (“hooked bone”) bones. The hamate bone is characterized by a prominent bony extension on its anterior side called the hook of the hamate bone. None of these articulate directly with the distal end of the ulna. In the articulated hand, the carpal bones form a U-shaped grouping held together by a strong ligament called the flexor retinaculum forming the passageway known as the carpal tunnel.

The palm of the hand contains five elongated metacarpal bones, numbered 1–5, beginning at the thumb. These bones lie between the carpal bones of the wrist and the bones of the fingers and thumb (see Figure 7.28). The proximal end of each metacarpal bone articulates with one of the carpal bones. The distal end forms the knuckles of the hand, at the base of the fingers. The first metacarpal bone, at the base of the thumb, is separated from the other metacarpal bones. This allows it a freedom of motion that is independent of the other metacarpal bones, which is very important for thumb mobility. The remaining metacarpal bones are united together to form the palm of the hand. The second and third metacarpal bones are firmly anchored in place and are immobile. However, the fourth and fifth metacarpal bones have limited anterior-posterior mobility, a motion that is greater for the fifth bone. This mobility is important during power gripping with the hand. The anterior movement of these bones, particularly the fifth metacarpal bone, increases the strength of contact for the medial hand during gripping actions. Metacarpal bones are properly named using the word metacarpal and its number. For example, the ring finger’s metacarpal is properly called metacarpal #4 or the 4th metacarpal bone.

The fingers and thumb contain 14 bones called phalanges (singular = phalanx), named after the ancient Greek phalanx (a rectangular block of soldiers). The thumb (pollex) is digit number 1 and has two phalanges, a proximal phalanx, and a distal phalanx bone (see Figure \(\PageIndex{28}\)). Digits 2 (index finger) through 5 (little finger) have three phalanges each, called the proximal, middle, and distal phalanx bones. Phalanges are properly named using the word phalanx, its position, and its number. For example, the ring finger’s phalanx that is at the tip of the finger is properly called distal phalanx #4 or the 4th distal phalanx.

For more information on the functions and features of specific bone markings for your lab, read: https://openstax.org/books/anatomy-and-physiology/pages/8-1-the-pectoral-girdle and https://openstax.org/books/anatomy-and-physiology/pages/8-2-bones-of-the-upper-limb

Figure \(\PageIndex{23}\): Humerus and elbow joint. The humerus is the single bone of the upper arm region. It articulates with the radius and ulna bones of the forearm to form the elbow joint.

Figure \(\PageIndex{24}\): Humerus-Posterior, )Photo Credit: Maky Orel, Source: https://commons.wikimedia.org/wiki/F..._posterior.jpg )

Figure \(\PageIndex{25}\): Ulna and Radius. The ulna is located on the medial side of the forearm, and the radius

Figure \(\PageIndex{26}\): Bones of the Wrist and Hand

Activity 7.4: Bones and Bone Markings of the Lower Appendicular Skeleton

Because of our upright stance, different functional demands are placed upon the upper and lower limbs. The bones of the lower limbs are adapted for weight-bearing support and stability, as well as for body locomotion via walking or running. This activity focuses on the bones of the lower limb, from the hip to the foot.

Procedure for Activity 7.4:

Use the information and figures that follow to identify the bones and required bone markings for the lower appendicular skeleton. These are listed in the objectives at the beginning of this lab.

The Pelvic Girdle & The Lower Limb

The pelvic girdle (hip girdle) is formed by a pair of coxal bones or os coxae bone (coxa = “hip”, singular). It is formed by the fusion of the ilium, ischium, and pubis/pubic bone. You should refer to each of these bones by their individual names for our course. Each coxal bone, in turn, is firmly joined to the axial skeleton via its attachment to the sacrum of the vertebral column. The right and left coxal bones are attached to each other anteriorly at a fibrous joint known as the pubic symphysis with a pad of fibrocartilage between them. The bony pelvis is the entire structure formed by the two coxal bones, the sacrum, and the coccyx. Unlike the bones of the pectoral girdle, the bones of the pelvis are strongly united to each other to form a largely immobile, weightbearing structure. This is important for stability because it enables the weight of the body to be easily transferred laterally from the vertebral column, through the pelvic girdle and hip joints, and into either lower limb whenever the other limb is not bearing weight. Thus, the immobility of the pelvis provides a strong foundation for the upper body as it rests on top of the mobile lower limbs. The leg contains thirty bones including the femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones, and fourteen phalanges.

The ilium is the fan-like, superior region of the coxal bone forming the largest part of the coxal bone (Figure \(\PageIndex{27}\), Figure \(\PageIndex{28}\)). When you place your hands on your waist, you can feel the arching, superior margin of the ilium along your waistline (Figure \(\PageIndex{27}\), 7.30). The ilium contains many important bone markings that serve as muscle and ligament attachments; furthermore, other bone markings allow the passage of nerves and blood vessels of the pelvis.

The ischium forms the posterolateral portion of the coxal bone (Figure \(\PageIndex{27}\), Figure \(\PageIndex{28}\)). Notably, the large, roughened area of the inferior ischium is the ischial tuberosity. This serves as the attachment for the posterior thigh muscles and carries the weight of the body when sitting. You can feel the ischial tuberosity if you wiggle your pelvis against the seat of a chair.

The pubis, or pubic bone, forms the anterior portion of the coxal bone (Figure \(\PageIndex{27}\), Figure \(\PageIndex{28}\)). Located superiorly on the pubic body is a small bump called the pubic tubercle. The superior pubic ramus is the segment of bone that passes laterally from the pubic body to join the ilium. The narrow ridge running along the superior margin of the superior pubic ramus is the pectineal line of the pubis.

Figure \(\PageIndex{27}\): Pelvis & Pelvic Girdle.

Figure \(\PageIndex{28}\): The Ilium (green), Ischium (orange), and Pubis (purple)

Differences Between the Female and Male Pelvis

As you have learned form (anatomy) and function (physiology) are inextricable! The striking differences between female and male pelves (pelvis = singular) are no exception. These structural differences are reflective of the functional differences between the average genetically female and genetically male bodies. Anatomists divide the pelvis into two regions (Figure \(\PageIndex{29}\)). The false pelvis is superior and is surrounded by iliac fossa portions of the coxal bones and the upper portion of the sacrum. The true pelvis is inferior and is surrounded by the pubis and ischium portions of the coxal bones, in addition to the lower sections of the ilium and the sacrum. In women, the true pelvis defines the space babies must squeeze through during childbirth.

Figure \(\PageIndex{29}\): The true pelvis vs. the false pelvis.

One of the few ways a skeleton stripped of all flesh can be reliably established as either male or female comes from examining the pelvis. The female pelvis can be distinguished from the male pelvis by a number or criterion, three of which are shown in Figure \(\PageIndex{30}\).

Most of these anatomical differences between the pelvises of males and females reflect the fact that only female pelvises have to serve as part of the birth canal, and these sex differences are not as pronounced in the skeletons of children who have not finished puberty.

In female pelvises, both the pelvic inlet and the pelvic outlet (not shown in Figure \(\PageIndex{30}\)) are wider and more oval-shaped than those in male pelvises. The pelvic inlet in males tends to be more heart-shaped (narrower on the dorsal side) and the pelvic outlet tends to be more narrow. The pubic arch, found immediately inferior to the pubic symphysis, tends to form an angle closer to 90° in females, but forms an angle closer to 60° in males. The sacrum in female pelvises tends to be less curved; in male pelvises, the sacrum is more curved and tends to impinge upon the space of the pelvic outlet.

Figure \(\PageIndex{30}\): Major differences that distinguish the adult male pelvis from the adult female pelvis

For more information on the functions and features of specific bone markings for your lab, read: https://openstax.org/books/anatomy-and-physiology/pages/8-3-the-pelvic-girdle-and-pelvis

The femur, the single bone of the thigh region (Figure \(\PageIndex{31}\)), is the longest and strongest bone of the body, and accounts for approximately one-quarter of a person’s total height. The rounded, proximal end is the head of the femur, which articulates with the acetabulum of the coxal bone to form the hip joint. The term “hip fracture” is a misnomer; this type of injury is actually a fracture of the neck of the femur, which connects its head to the rest of the bone. The femur contains several markings that are used for ligament, tendon, and muscle attachments related to posture, hip movement, trunk stability, and walking. As you examine the femur, notice its many bumps and ridges; although some of these may appear small or subtle, they are critical attachments for muscles that allow us to run for safety or jump for joy.

The patella (known as the kneecap in layman’s language) is largest sesamoid bone of the body (Figure \(\PageIndex{31}\)). A sesamoid bone is a bone that is incorporated into the tendon of a muscle where that tendon crosses a joint. A sesamoid bone functions to articulate with the underlying bones to prevent damage to the muscle tendon due to rubbing against the bones during joint movement. The patella is found in the tendon of the quadriceps femoris muscle, the large muscle of the anterior thigh that passes across the anterior knee to attach to the tibia. The patella also lifts the tendon away from the knee joint, which increases the leverage power of the quadriceps femoris muscle as it acts across the knee. The patella does not articulate with the tibia.

The tibia is the medial bone of the lower leg and is larger (circumferentially) than the fibula, with which it is paired (Figure \(\PageIndex{32}\)). The tibia is the main weight-bearing bone of the lower leg and the second longest bone of the body after the femur. The tibial contains several bone markings that serve as attachment points for thick ligaments and tendons as well as powerful muscles of the leg. Many of these can be easily palpated, including the tibial tuberosity (inferior to the medial part of the patella), the anterior border (a superficial ridge of bone that people refer to as the shin when this area is banged against something), and the medial malleolus (“little hammer”, a large bony bump found on the medial side of the ankle region). On the lateral side of the distal tibia is a wide groove called the fibular notch. This area articulates with the distal end of the fibula, forming the distal tibiofibular joint.

The fibula is the slender bone located on the lateral side of the leg (Figure \(\PageIndex{32}\)). The fibula does not bear weight; it serves primarily for muscle attachments and is, thus, largely surrounded by muscles. Only the proximal and distal ends of the fibula can be palpated. The distal end of the fibula forms the lateral malleolus, which forms the easily palpated bony bump on the lateral side of the ankle.

The posterior half of the foot and part of the ankle are formed by seven tarsal bones (Figure \(\PageIndex{33}\)). Body weight is transferred from the tibia to the talus to the calcaneus, which rests on the ground. The seven tarsal bones consist of talus, calcaneus, cuboid, navicular, medial cuneiform, intermediate cuneiform, and lateral cuneiform.

The anterior half of the foot is formed by the five metatarsal bones, which are located between the tarsal bones and the phalanges of the toes (Figure \(\PageIndex{33}\)). These elongated bones are numbered 1–5, starting with the medial side of the foot. Each metatarsal bone articulates with the proximal phalanx of a toe to form a metatarsophalangeal joint. The heads of the metatarsal bones also rest on the ground and form the ball (anterior end) of the foot. Metatarsal bones are properly named using the word metatarsal and its number. For example, the big toe’s metatarsal is properly called metatarsal #1 or the 1st metatarsal bone.

The toes contain a total of 14 phalanx bones (phalanges), arranged in a similar manner as the phalanges of the fingers (see Figure \(\PageIndex{33}\)). The toes are numbered 1–5, starting with the big toe (hallux) on the medial side of the foot. The big toe has two phalanx bones, the proximal and distal phalanges. The remaining toes all have proximal, middle, and distal phalanges. A joint between adjacent phalanx bones is called an interphalangeal joint. Phalanges are properly named using the word phalanx, its position, and its number. For example, the big toe’s phalanx that is closest to the ankle is properly called proximal phalanx #1 or the 1st proximal phalanx.

For more information on the functions and features of specific bone markings for your lab, read: https://openstax.org/books/anatomy-and-physiology/pages/8-4-bones-of-the-lower-limb