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Newborn skeleton

Lateral view

 1 Cranial bones

 2 Vertebral column

 3 Ribs

 4 Clavicle

 5 Scapula

 6 Humerus

 7 Ulna

 8 Radius

 9 Carpals

10 Metacarpals

 11 Phalanges

12 Os coxae

13 Femur

14 Patella

15 Tibia

16 Fibula

17 Tarsals

18 Metatarsals

Adult skeleton

Lateral view

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Th e axial skeleton, comprised of the skull, vertebral column,

ribs, and sternum, forms the central axis of the

body. Th is sturdy central core is the most primitive portion of the vertebrate skeletal system. It

evolved as the initial skeleton of the fi rst vertebrate

animals, to which the limb bones (the subject of

the next chapter) were much later additions. Th e

majority of the axial skeleton’s bony elements, from

the bones at the base of the skull through all the

vertebrae and ribs, form as serial homologues from the

segmental embryonic somites. Because of this shared

developmental similarity each body segment, from the

base of the skull to the end of the coccyx, has the same

basic skeletal design. Th is is clearly evident in the

structure of the vertebrae and ribs. As you study these

skeletal elements in the photos of this chapter, notice

their similarities.

Th e elements of the axial skeleton have

many functional roles in the body. Both the

cranial skeleton and the vertebral column

form a strong protective case around the

delicate tissues of the central nervous system.

 Additionally, the cranium fi xes in space important nervous structures, such as the internal

ear and eye, both of which would not function

properly in an unstable environment. Th e cranium also plays an important role in the acquisition and processing of food, respiratory gases,

and sensory input such as sound. In addition to

protecting the spinal cord, the vertebrae form a

strong, fl exible rod. Th is strong, fl exible column not only

forms the central support axis of the body from which

the limbs are suspended, but is also capable of a varied

range of joint movements that are essential to our daily

functions.

Find more information

about the axial skeleton in

5 Axial Skeleton

33

REAL ANATOMY

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 1 Cranium

 2 Hyoid bone

 3 Cervical vertebral column

 4 Cervical vertebra 1 - Atlas

 5 Cervical vertebra 2 - Axis

 6 Cervical vertebra 7

 7 Thoracic vertebral column

 8 Thoracic vertebra 1

 9 Thoracic vertebra 12

10 Lumbar vertebral column

 11 Lumbar vertebra 1

12 Lumbar vertebra 5

13 Sacrum

14 Sternum

15 Ribs

Axial skeleton

Anterior view

The axial skeleton is clearly depicted in the photos below. Note

that this portion of the skeleton consists of three principal

skeletal regions — the cranium, the vertebral column, and the

Axial Skeleton

rib cage. There are 29 cranial bones, 26 vertebral bones, and 25 bones in the rib cage. On the pages that

follow, each of the axial skeletal regions and the respective bones will be explored in greater detail.

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Axial skeleton

Lateral view Axial skeleton

Posterior view

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 1 Frontal bone

 2 Parietal bone

 3 Occipital bone

 4 Sphenoid bone

 5 Temporal bone

 6 Ethmoid bone

 7 Inferior nasal concha

 8 Lacrimal bone

 9 Nasal bone

10 Vomer

 11 Maxilla

12 Palatine bone

13 Zygomatic bone

14 Mandible

15 Bony nasal cavity

16 Piriform aperture

17 Inferior nasal meatus

18 Middle nasal meatu

19 Orbit

Cranium

Anterior view

functions, that include protecting the delicate brain tissue, fi xing the vestibular apparatus of the inner ear in

three-dimensional space, maintaining open air passageways for respiration, and acquiring and processing

food, to name a few. There are two main subdivisions of the cranium — the neurocranium or brain box is the

region that surrounds and encases the brain, and the viscerocranium or facial skeleton is the area contributing

to the orbits, nasal cavity, and oral cavity. This page and the facing page, and the four page spreads that follow,

depict the fi ve normas, or views, of the cranium in both articulated and disarticulated cranial images. The

bones of the skull are labeled on these views, along with key landmarks that can only be labeled on the articulated cranium. Individual landmarks of the bones are labeled on the individual pictures of the cranial bones on

the pages that follow. This spread is of the norma facialis or facial aspect of the cranium.

The cranium is the composite skeleton of the head and is composed of 29 bones.

The bones of the cranium range from simple, non-descript plates of bone to the

most intricate bones of the skeleton. The cranial bones have a range of important

Cranium

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Bones of the cranium disarticulated

Anterior view

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 1 Frontal bone

 2 Parietal bone

 3 Occipital bone

 4 Sphenoid bone

 5 Temporal bone

 6 Ethmoid bone

 7 Lacrimal bone

 8 Nasal bone

 9 Maxilla

10 Zygomatic bone

 11 Mandible

12 Zygomatic arch

13 Pterygopalatine fossa

Cranium

Cranium

Lateral view

This page spread depicts the norma lateralis, or lateral aspect of the cranium. In this view both

the brain box and facial skeleton are clearly visible and the relative proportions of the two cranial

regions are evident. In the disarticulated view, only those bones that are visible in the lateral aspect are shown.

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Bones of the cranium disarticulated

Lateral view

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Cranium

 1 Parietal bone

 2 Occipital bone

 3 Sphenoid bone

 4 Temporal bone

 5 Ethmoid bone

 6 Inferior nasal concha

 7 Vomer

 8 Maxilla

 9 Palatine bone

10 Zygomatic bone

 11 Mandible

12 Choana or posterior nasal aperture

13 Inferior orbital fissure

14 Bony nasal cavity

15 Middle nasal meatus

16 Inferior nasal meatus

17 Bony palate

18 Sutural bone

Cranium

Posterior view

This page spread depicts the norma occipitalis, or occipital aspect of the cranium. From this posterior view the internal aspects of the bones of the oral and nasal cavities are clearly visible. In the

disarticulated view only those bones that are visible in the occipital aspect of the cranium are

depicted.

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Bones of the cranium disarticulated

Posterior view

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Cranium

 1 Frontal bone

 2 Parietal bone

 3 Occipital bone

 4 Temporal bone

 5 Nasal bone

 6 Maxilla

 7 Zygomatic bone

Cranium

Superior view

This page spread depicts the norma superior, or superior aspect of the cranium. This view clearly

depicts the neurocranium or brain box, while the facial skeleton is almost completely hidden from

view. In the disarticulated view only those bones that are visible in the superior aspect of the cranium

are depicted.

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Bones of the cranium disarticulated

Superior view

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Cranium

 1 Occipital bone

 2 Sphenoid bone

 3 Temporal bone

 4 Vomer

 5 Maxilla

 6 Palatine bone

 7 Zygomatic bone

 8 Bony palate

 9 Choana or posterior nasal aperture

10 Zygomatic arch

 11 Jugular foramen

12 Foramen lacerum

13 Greater palatine foramen

14 Incisive fossa

Cranium

Inferior view

This page spread depicts the norma inferior (basalis), or inferior aspect of the cranium. The mandible has been removed to more clearly reveal the basicranium. This view clearly depicts the fl oor

of the brain box, the bony palate forming the roof of the oral cavity, and mandibular tooth row. In

the disarticulated view only those bones that are visible in the inferior aspect of the cranium are

depicted.

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Bones of the cranium disarticulated

Inferior view

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Cranium

Parasagittal section of the cranium

Medial view of the right side

This page spread depicts the cranium sectioned in a parasagittal plane through the right side of

the nasal cavity just lateral to the bony nasal septum. The section below depicts the lateral wall of

the right nasal cavity, and the section on the opposite page depicts the medial (septal) wall of the

right nasal cavity. The osseous sinuses that communicate with the nasal cavity are all visible in

these sections.

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 1 Frontal bone

 2 Parietal bone

 3 Occipital bone

 4 Sphenoid bone

 5 Temporal bone

 6 Ethmoid bone

 7 Inferior nasal concha

 8 Nasal bone

 9 Vomer

10 Maxilla

 11 Palatine bone

12 Mandible

19 Ethmoidal air cells (sinuses)

20 Maxillary sinus

21 Incisive canal

22 Bony nasal septum

23 Sphenopalatine foramen

24 Inferior nasal meatus

Parasagittal section of the cranium

Medial view of the left side

13 External table of calvaria

14 Diploë

15 Internal table of calvaria

16 Groove for sigmoid sinus

17 Sphenoidal sinus

18 Frontal sinus

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Cranium

Cranium with calvaria removed

Superior or internal view of the cranial base

This page spread depicts the cranium sectioned in a horizontal plane through the neurocranium,

or brain box, revealing the internal aspects of the fl oor and roof of the sectioned cranial cavity. On

this page the fl oor of the neurocranium is visible, while on the opposing page the roof of the neurocranium is visible. The superior portion of the cranium, depicted on the opposite page, is called

the calvaria.

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 1 Frontal bone

 2 Parietal bone

 3 Occipital bone

 4 Sphenoid bone

 5 Temporal bone

 6 Ethmoid bone

 7 Clivus

 8 Foramen caecum

 9 Foramen lacerum

10 Jugular foramen

 11 Petrosphenoidal fissure

12 Petro-occipital fissure

13 Anterior cranial fossa

14 Middle cranial fossa

15 Posterior cranial fossa

16 Granular foveolae

Removed calvaria

Inferior or internal view

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Cranial Bones – Frontal

 1 Squamous part

 2 Frontal tuber

 3 Glabella

 4 Superciliary arch

 5 Supra-orbital notch or foramen

 6 Frontal notch or foramen

 7 Temporal surface

 8 Zygomatic process

 9 Frontal crest

10 Groove for superior sagittal sinus

 11 Nasal spine

12 Orbital surface

13 Trochlear spine

14 Lacrimal fossa

15 Ethmoidal notch

16 Frontal sinus

Frontal bone

Posterior view

Frontal bone

Anterior view

vertical portion termed the squama and a horizontal plate that forms the superior walls of the orbits.

The bone has a smooth external surface, while its internal surface consists of impressions made by the

meningeal vessels and scattered foramina that transmit diploic vessels. The squamous portion of the

bone is thick. It consists of internal and external laminae of compact bone sandwiching a layer of trabecular bone called diploë. Near the anterior, inferior midline the spongy bone is absent between the

external and internal laminae and in its place are variably sized spaces — the frontal sinuses. The orbital

plate consists of a thin plate of compact bone, which is often so thin that it is translucent. The frontal

bone articulates with twelve bones.

The unpaired frontal bone has a

bowl-like shape that consists of

two parts, an internally concave

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