Axial skeleton

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Bones of the cranium disarticulated

Anterior view

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Cranium 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.

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

10Zygomatic bone

11Mandible

12Zygomatic arch

13Pterygopalatine fossa

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Cranium

Lateral view

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Bones of the cranium disarticulated

Lateral view

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Cranium 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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Cranium

Posterior view

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Bones of the cranium disarticulated

Posterior view

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Cranium 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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Cranium

Superior view

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Bones of the cranium disarticulated

Superior view

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Cranium 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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Cranium

Inferior view

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Bones of the cranium disarticulated

Inferior view

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Cranium 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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Parasagittal section of the cranium

Medial view of the right side

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Parasagittal section of the cranium

Medial view of the left side

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Cranium 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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Cranium with calvaria removed

Superior or internal view of the cranial base

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Removed calvaria

Inferior or internal view

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The unpaired frontal bone has a bowl-like shape that consists of two parts, an internally concave

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.

Frontal bone

Posterior view

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Frontal bone

Inferior view, anterior to top

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Frontal bone

Lateral view, anterior to left

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Left parietal bone

Inferior view, anterior to right

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The occipital bone forms the greater part of the posterior and inferior cranium. Viewed from

behind it has an oval to round shape. The bone has four distinct regions. The squamous portion is the internally concave posterosuperior plate and forms the greater part of the bone. The thick quadrilateral basioccipital, or basilar part, contributes to the base of the cranium anterior to the foramen magnum. Lateral to this and converging with the squama are the two condylar parts or exoccipitals. Together the four regions of the bone form the borders to the large circular opening, the foramen magnum, which provides passage for the spinal cord between the cranial vault and the spinal canal. The occipital bone articulates with six bones.

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Occipital bone 3

Lateral view, anterior to right

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Sphenoid bone

Lateral view, anterior to left

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Mandible

Inferior view, anterior at bottom

Mandible

Lateral view, anterior to right

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The term ethmoid comes from the Greek term ethmos meaning sieve. Galen called the bone the

sieve-like bone because of the many small foramina that transmit the olfactory nerves to the nasal cavity. This unpaired bone is both complex and delicate and is the central bone of the nasal cavity. Wedged between the two orbits, the bone consists of a median vertical plate, a horizontal plate perforated by many small foramina, and bilateral pneumatic, labyrinthine regions. The labyrinthine regions form most of the medial walls of the orbit and the superior and middle nasal conchae. This bone consists of thin laminae of compact bone surrounding many small air sinuses, which communicate with the nasal cavity. The ethmoid bone articulates with thirteen bones, more articulations than any other cranial bone.

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The zygomatic bone, originally named by Galen the os zygoma, comes from

the Greek word zygon meaning yoke, after its resemblance to a yoke placed on oxen. This yoke-shaped bone has three distinct surfaces, fi ve borders, and two processes. It is situated anterolateral on the face as the “cheekbone”, and contributes to the lateral and inferior walls of the orbit. It consists of external and internal laminae of compact bone with an inner core of spongy bone. The zygomatic bone articulates with four bones.

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The palatine bone is a delicate and intricate bone that forms the shape of the letter L. It sits deep

in the posterior facial region where it contributes to the roof of the mouth, fl oor of the orbit, fl oor and lateral walls of the nasal cavity, and to the pterygopalatine fossa. It has a strong horizontal plate with a delicate vertical lamina that projects superiorly. The palatine bone articulates with six bones.

The paired nasal bones are small, rectangular bones with a subtle bow-like shape. They form the bridge of the nose

upon which a pair of eye glasses rest. The external surface of the bones provides attachment for the procerus and nasalis muscles, two thin muscles of facial expression. Each nasal bone articulates with four bones.

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