Human Anatomy & Physiology, Sixth Edition

7The Skeleton

Part A

The Axial Skeleton

Eighty bones segregated into three regions Skull Vertebral column Bony thorax

The Skull

The skull Cranium

Eight cranial bones – 2 parietal, 2 temporal, frontal, occipital, sphenoid, and

ethmoid Facial bones

Fourteen bones 2 maxillae, 2 zygomatics, 2 nasals, 2 lacrimals, 2 palatines,

and 2 inferior conchae mandible and vomer are unpaired

Skull: Anterior View

Figure 7.2a

Skull: Lateral View

Figure 7.3a

Skull: Posterior View

Figure 7.2b

Inferior Portion of the Skull

Figure 7.4a

Paranasal Sinuses

Figure 7.11

Vertebral Column

26 irregular bones 7 Cervical vertebrae 12 Thoracic vertebrae 5 Lumbar vertebrae Sacrum – 5 fused bones Coccyx – 4 fused bones

Vertebral Column: Ligaments

Anterior (ventral) and posterior (dorsal) longitudinal ligaments Short ligaments connect adjoining vertebrae together

General Structure of Vertebrae

Figure 7.15

Vertebral Column: Intervertebral Discs

Nucleus pulposus – inner gelatinous region Annulus fibrosus – collar of collagen and

fibrocartilage

Cervical Vertebrae: The Atlas (C1)

Figure 7.16a, b

Cervical Vertebrae: The Axis (C2)

Figure 7.16c

Cervical Vertebrae

Figure 7.17a

Sacrum and Coccyx: Posterior (dorsal) View

Figure 7.18b

Thorax (Thoracic Cage)

The thoracic cage Dorsal - thoracic vertebrae

Laterally - ribs

Ventral - sternum and costal cartilages

Functions Protective cage around the heart,

lungs, and great blood vessels

Supports the pectoral girdle and upper limbs

Attachment sites for neck, back, chest, and shoulder muscles

Intercostal muscles lift and depress the thorax for breathing

Thorax: Sternum

Fusion of three bones manubrium, sternal body, xiphoid process

Thorax: Ribs

12 pairs All attached dorsally to the

thoracic vertebrae Vertebrosternal ribs –attach

to sternum via costal cartilages – “true ribs”

Vertebrochondral ribs - attach to costal cartilage of rib 7 – “false ribs”

Vertebral ribs - no ventral attachment – “floating ribs”

Pectoral Girdle (Shoulders)

Figure 7.22a

Scapulae (Shoulder Blades)

Figure 7.22d, e

The Upper Limb

The proximal arm (brachium), distal arm (forearm; antebrachium), and hand (manus)

Thirty-seven bones

Humerus of the Proximal Arm

Figure 7.23

Radia and Ulna of the Distal Arm (Forearm)

Figure 7.24

Manus (Hand)

Figure 7.26a

14

5

8

Pelvic Girdle (Hips)

Os coxae - coxal bones Coxal bone is fusion of 3 bones – ilium, ischium, pubis Os coxae, sacrum and coccyx, form the bony pelvis

Os coxa: Lateral View

Obturator foramen

Comparison of Male and Female Pelvic Structure

Female pelvis Tilted forward, adapted for

childbearing Pubic arch obtuse angle Cavity of the true pelvis is

broad, shallow,

Male pelvis Less tilted forward Pubic arch acute angle Cavity of true pelvis is narrow

and deep

The Lower Limb

the thigh (proximal), leg (distal), and foot

Femur

Figure 7.28b

Tibia and Fibula

Figure 7.29

Foot

Figure 7.31b, c

7

5

14

Developmental Aspects: Fetal Skull

At birth, fetal skull bones are incomplete and connected by fontanels

Fontanels Unossified remnants

of fibrous membranes between bones

anterior, posterior mastoid sphenoid

Figure 7.33

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

Developmental Aspects: Growth Rates

Figure 7.34