Chapter 7

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

The Axial & Appendicular Skeleton

Axial Components

Eighty bones segregated into three regions

Skull

Vertebral column

Bony thorax


The Skull

The skull, the body’s most complex bony structure, is formed by the cranium and facial bones

Cranium – protects the brain and is the site of attachment for head and neck muscles

Facial bones

Supply the framework of the face, the sense organs, and the teeth

Provide openings for the passage of air and food

Anchor the facial muscles of expression


External Lateral Aspects of the Skull

Figure 7.3a

(a)

Coronal suture Frontal bone

Sphenoid bone(greater wing)

Ethmoid bone

Lacrimal bone

Lacrimal fossa

Nasal bone

Zygomatic bone

Maxilla

Alveolar margins

MandibleMental foramen

Parietal bone

Lambdoidsuture

Squamous suture

Occipital bone

Occipitomastoid suture

External acoustic meatus

Mastoid process

Styloid process

Mandibular condyle

Mandibular notch

Mandibular ramus

Mandibular angle Coronoid process

Zygomatic process

Temporal bone


Anterior Aspects of the Skull

Figure 7.2a(a)

Parietal bone

Frontal squamaof frontal bone

Nasal bone

Sphenoid bone(greater wing)Temporal bone

Ethmoid bone

Lacrimal bone

Zygomatic bone

Maxilla

Mandible

Infraorbital foramen

Mentalforamen

Mandibular symphysis

Frontal bone

Glabella

Frontonasal suture

Supraorbital foramen(notch)

Supraorbital marginSuperior orbitalfissure

Inferior orbitalfissure

Middle nasal conchaPerpendicular plate

Inferior nasal concha

Vomer bone

Optic canal

Ethmoidbone


Sphenoid Bone

Figure 7.6b


Nasal Cavity

Figure 7.10a


Nasal Cavity

Figure 7.10b


Paranasal Sinuses

Figure 7.11


Hyoid Bone

Not actually part of the skull, but lies just inferior to the mandible in the anterior neck

Only bone of the body that does not articulate directly with another bone

Attachment point for neck muscles that raise and lower the larynx during swallowing and speech


Vertebral Column

Formed from 26 irregular bones (vertebrae) connected in such a way that a flexible curved structure results

Cervical vertebrae – 7 bones of the neck

Thoracic vertebrae – 12 bones of the torso

Lumbar vertebrae – 5 bones of the lower back

Sacrum – bone inferior to the lumbar vertebrae that articulates with the hip bones


Vertebral Column

Figure 7.13


General Structure of Vertebrae

Figure 7.15


Cervical Vertebrae

Table 7.2.2

Seven vertebrae (C1-C7) are the smallest, lightest vertebrae

C3-C7 are distinguished with an oval body, short spinous processes, and large, triangular vertebral foramina

Each transverse process contains a transverse foramen


Cervical Vertebrae: The Atlas (C1)

Figure 7.16a, b

The atlas has no body and no spinous process

It consists of anterior and posterior arches, and two lateral masses

The superior surfaces of lateral masses articulate with the occipital condyles


Cervical Vertebrae: The Axis (C2)

Figure 7.16c

The axis has a body, spine, and vertebral arches as do other cervical vertebrae

Unique to the axis is the dens, or odontoid process, which projects superiorly from the body and is cradled in the anterior arch of the atlas

The dens is a pivot for the rotation of the atlas


Vertebral Column: Ligaments

Figure 7.14a


Vertebral Column: Intervertebral Discs

Figure 7.14b


Regional Characteristics of Vertebrae

Table 7.2.2


Sacrum

Sacrum

Consists of five fused vertebrae (S1-S5), which shape the posterior wall of the pelvis

It articulates with L5 superiorly, and with the auricular surfaces of the hip bones

Major markings include the sacral promontory, transverse lines, alae, dorsal sacral foramina, sacral canal, and sacral hiatus


Coccyx

Coccyx (Tailbone)

The coccyx is made up of four (in some cases three to five) fused vertebrae that articulate superiorly with the sacrum


Sacrum and Coccyx: Anterior View

Figure 7.18a


Bony Thorax (Thoracic Cage)

Figure 7.19a


Structure of a Typical True Rib

Bowed, flat bone consisting of a head, neck, tubercle, and shaft

Figure 7.20a


Structure of a Typical True Rib

Bowed, flat bone consisting of a head, neck, tubercle, and shaft

Figure 7.20b


Appendicular Skeleton

The appendicular skeleton is made up of the bones of the limbs and their girdles

Pectoral girdles attach the upper limbs to the body trunk

Pelvic girdle secures the lower limbs


Pectoral Girdles (Shoulder Girdles)

The pectoral girdles consist of the anterior clavicles and the posterior scapulae

They attach the upper limbs to the axial skeleton in a manner that allows for maximum movement

They provide attachment points for muscles that move the upper limbs


Pectoral Girdles (Shoulder Girdles)

Figure 7.22a


Clavicles (Collarbones)

Figure 7.22b, c


Scapulae (Shoulder Blades)

Figure 7.22d


Scapulae (Shoulder Blades)

Figure 7.22f


Humerus of the Arm

Figure 7.23


Bones of the Forearm

Figure 7.24


Radius and Ulna

Figure 7.24


Hand

Skeleton of the hand contains wrist bones (carpals), bones of the palm (metacarpals), and bones of the fingers (phalanges)

Figure 7.26a


Comparison of Male and Female Pelves

Table 7.4.1


Comparison of Male and Female Pelvic Structure

Female pelvis

Tilted forward, adapted for childbearing

True pelvis defines birth canal

Cavity of the true pelvis is broad, shallow, and has greater capacity



Male pelvis

Tilted less forward

Adapted for support of heavier male build and stronger muscles

Cavity of true pelvis is narrow and deep



Image from Table 7.4


Comparison of Male and Female Pelves

Table 7.4.2


Characteristic Female Male

Bone thickness Lighter, thinner, and smootherHeavier, thicker, and more prominent markings

Pubic arch/angle 80˚–90˚ 50˚–60˚

Acetabula Small; farther apart Large; closer together

SacrumWider, shorter; sacral curvature is accentuated

Narrow, longer; sacral promontory more ventral

Coccyx More movable; straighterLess movable; curves ventrally



Pelvic Girdle (Hip)

Figure 7.27a


Ilium: Lateral View

Figure 7.27b


Ilium: Medial View

Figure 7.27c


Femur

Figure 7.28b


Tibia and Fibula

Figure 7.29


Foot

The skeleton of the foot includes the tarsus, metatarsus, and the phalanges (toes)

The foot supports body weight and acts as a lever to propel the body forward in walking and running

Figure 7.31a


Tarsus

Figure 7.31b, c


Arches of the Foot

Figure 7.32


Developmental Aspects: Fetal Skull

Skull bones such as the mandible and maxilla are unfused

Figure 7.33


Developmental Aspects: Growth Rates

At birth, the cranium is huge relative to the face

Mandible and maxilla are foreshortened but lengthen with age

The arms and legs grow at a faster rate than the head and trunk, leading to adult proportions

Figure 7.34


Developmental Aspects: Spinal Curvature

Only thoracic and sacral curvatures are present at birth

The primary curvatures are convex posteriorly, causing the infant spine to arch like a four-legged animal

Secondary curvatures – cervical and lumbar – are convex anteriorly and are associated with the child’s development


Developmental Aspects: Old Age

Intervertebral discs become thin, less hydrated, and less elastic

Risk of disc herniation increases

Loss of stature by several centimeters is common after age 55

Costal cartilages ossify causing the thorax to become rigid

All bones lose mass

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