The Human Skeleton: Axial and Appendicular Divisions, Skull Anatomy, and Cranial Bones

The Human Skeleton

Overview of Skeletal Divisions

The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. Understanding these divisions is essential for studying the structure and function of bones in Anatomy & Physiology.

• Axial Skeleton: Consists of the skull, vertebral column, and thoracic cage (ribs and sternum).

• Appendicular Skeleton: Includes the bones of the limbs and the girdles (pectoral and pelvic) that attach them to the axial skeleton.

• Clavicle: Although it forms part of the appendicular skeleton, its articulation with the sternum connects it to the axial skeleton.

Example: The scapula and clavicle form the pectoral girdle, connecting the upper limb to the axial skeleton.

Skull Anatomy

Major Regions and Bones of the Skull

The skull is a complex structure composed of several bones that protect the brain and form the face. It is divided into the cranium and the facial bones.

• Cranium: Encloses and protects the brain. Includes bones such as the frontal, parietal, temporal, occipital, sphenoid, and ethmoid.

• Facial Bones: Form the structure of the face. Includes the maxilla, mandible, zygomatic, nasal, lacrimal, palatine, inferior nasal concha, and vomer.

• Orbits: The bony sockets that house the eyes, formed by contributions from both cranial and facial bones.

Example: The mandible is the only movable bone of the skull, forming the lower jaw.

Cranial Bones: Identification and Features

There are eight cranial bones, each with distinct features and functions. Recognizing these bones and their locations is crucial for understanding skull anatomy.

• Frontal Bone: Forms the forehead and the superior part of the orbits.

• Parietal Bones (2): Form the sides and roof of the cranial cavity.

• Temporal Bones (2): House the structures of the ears and form the lateral aspects of the skull.

• Occipital Bone: Forms the posterior part of the skull and contains the foramen magnum.

• Sphenoid Bone: Located at the base of the skull, articulates with many other cranial bones.

• Ethmoid Bone: Forms part of the nasal cavity and the orbits.

Example: The occipital bone contains the foramen magnum, through which the spinal cord passes.

Facial Bones: Identification and Features

There are fourteen facial bones, which form the structure of the face and support the teeth.

• Maxilla (2): Forms the upper jaw and part of the orbits and nasal cavity.

• Mandible: Forms the lower jaw and is the only movable bone of the skull.

• Zygomatic Bones (2): Form the cheekbones and part of the orbits.

• Nasal Bones (2): Form the bridge of the nose.

• Lacrimal Bones (2): Small bones forming part of the medial wall of each orbit.

• Palatine Bones (2): Form part of the hard palate and nasal cavity.

• Inferior Nasal Conchae (2): Form part of the lateral walls of the nasal cavity.

• Vomer: Forms part of the nasal septum.

Example: The zygomatic bones articulate with the maxilla, temporal bone, and sphenoid bone to form the prominence of the cheek.

Special Features and Articulations

Understanding the articulations and special features of skull bones is important for recognizing their roles in protection, movement, and sensory function.

• Sutures: Immovable joints that connect the bones of the skull.

• Foramina: Openings in the bones that allow passage of nerves and blood vessels (e.g., foramen magnum, supraorbital foramen).

• Sinuses: Air-filled cavities within certain skull bones that reduce weight and contribute to voice resonance.

Example: The coronal suture connects the frontal bone to the parietal bones.

Table: Cranial and Facial Bones

The following table summarizes the main cranial and facial bones, their number, and key features.

Bone	Type	Number	Key Features
Frontal	Cranial	1	Forehead, superior orbits
Parietal	Cranial	2	Sides and roof of cranium
Temporal	Cranial	2	Lateral skull, ear structures
Occipital	Cranial	1	Posterior skull, foramen magnum
Sphenoid	Cranial	1	Base of skull, articulates with many bones
Ethmoid	Cranial	1	Nasal cavity, orbits
Maxilla	Facial	2	Upper jaw, orbits, nasal cavity
Mandible	Facial	1	Lower jaw, only movable skull bone
Zygomatic	Facial	2	Cheekbones, orbits
Nasal	Facial	2	Bridge of nose
Lacrimal	Facial	2	Medial wall of orbit
Palatine	Facial	2	Hard palate, nasal cavity
Inferior Nasal Concha	Facial	2	Lateral wall of nasal cavity
Vomer	Facial	1	Nasal septum

Additional Info

• Additional info: The notes reference the importance of learning bone colors and features for practical identification, which is a common approach in anatomy labs.

• Additional info: The discussion of sinuses and foramina is expanded for academic completeness.