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Bone Classification, Markings, and Skull Anatomy: Medical Terminology Study Guide

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Bone Classification and the Human Skeleton

Axial and Appendicular Skeletons

The adult human skeleton consists of 206 named bones, divided into two main groups: the axial and appendicular skeletons. Understanding these divisions is fundamental for medical terminology and anatomy.

  • Axial Skeleton: Includes the bones of the skull, vertebral column, and rib cage. Functions primarily in protection, support, and carrying body structures.

  • Appendicular Skeleton: Comprises the bones of the upper and lower limbs and the girdles (shoulder and hip bones). Responsible for locomotion and manipulation of the environment.

Bone Shape Classification

Bones are classified based on their shapes, which relate to their functions and locations.

  • Long Bones: Longer than they are wide; have a cylindrical shaft. Most limb bones (e.g., femur, humerus).

  • Short Bones: Cube-shaped; equal length and width. Example: carpals, tarsals.

  • Sesamoid Bones: Shaped like sesame seeds, form within tendons (e.g., patella).

  • Flat Bones: Thin, curved, and flat. Example: cranial bones, sternum.

  • Irregular Bones: Complicated shapes. Example: vertebrae, hip bones.

Bone Markings and Features

Bone Markings: Projections, Depressions, and Openings

Bone markings are anatomical features that serve as attachment sites for muscles, ligaments, and tendons, or as passageways for nerves and blood vessels. They are essential for understanding skeletal anatomy and medical terminology.

  • Processes (Projections or Outgrowths): Form attachment sites for connective tissue or help form joints.

  • Depressions and Openings: Allow passage of blood vessels and nerves or serve as articulation points.

Table: Bone Markings and Descriptions

Process (Projection or Outgrowth)

Description

Tuberosity

Large, rounded, usually rough projection

Crest

Prominent ridge

Trochanter

Very large projection

Linea (means "line")

Long, narrow ridge

Tubercle (means "knob")

Small, rounded projection

Epicondyle (means "above"/"upon")

Projection above or on a condyle

Spine

Sharp, slender projection

Process

Any bony prominence

Processes that help to form joints

Head

Rounded, articular projection atop a narrower neck

Facet

Small, smooth surface

Condyle (means "knuckle")

Large, round projection

Depression or Opening

Description

Fossa (si.), Fossae (pl.) (means "trench")

Depression(s); shallow, basin-like

Sulcus (means "groove")

Shallow groove

Meatus (means "channel")

Tube-like opening

Groove

Furrow

Fissure

Narrow, slit-like opening

Notch

Indentation at the edge of a structure

Bone markings table Bone markings table (depressions and openings)

Skull Anatomy

Cranial Bones

The skull is composed of 8 cranial bones and 14 facial bones, most of which are flat bones. Cranial bones protect the brain and provide attachment sites for head and neck muscles.

  • Frontal Bone

  • Parietal Bones

  • Occipital Bone

  • Temporal Bones

  • Sphenoid Bone

  • Ethmoid Bone

Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views

Facial Bones

Facial bones form the structure of the face and house the teeth.

  • Maxillae (Maxillary Bones)

  • Zygomatic Bones

  • Nasal Bones

  • Lacrimal Bones

  • Vomer

  • Inferior Nasal Conchae

  • Palatine Bones

  • Mandible

Labeled facial bones, anterior view Labeled facial bones, anterior view

Ethmoid Bone Features

The ethmoid bone is a complex bone located between the eyes, contributing to the medial wall of the orbit, the nasal cavity, and the nasal septum.

  • Perpendicular Plate: Forms part of the nasal septum.

  • Middle Nasal Conchae: Increase surface area in the nasal cavity.

  • Cribriform Plate: Contains foramina for olfactory nerves.

  • Crista Galli: Attachment for the falx cerebri (dura mater).

Ethmoid bone features Ethmoid bone features

Processes and Fossae of the Skull

Various processes and fossae are found throughout the skull, serving as attachment points and passageways.

  • Alveolar Processes: Hold teeth in the maxilla and mandible.

  • Zygomatic Arches: Formed by the zygomatic bone and the zygomatic process of the temporal bone.

  • Mastoid and Styloid Processes: Located on the temporal bone, serve as muscle attachment sites.

  • Mandibular Fossa: Articulates with the condylar process of the mandible.

  • Occipital Condyles: Articulate with the first cervical vertebra.

  • External Occipital Protuberance: Prominent projection on the occipital bone.

Skull processes and fossae Skull processes and fossae Skull processes and fossae Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Mastoid, styloid, occipital processes Mastoid, styloid processes Squamous and petrous portions of temporal bone

Foramina of the Skull

Foramina are openings in bones that allow the passage of nerves and blood vessels.

  • Foramen Magnum: Large opening in the occipital bone for the spinal cord.

  • Optic Canal (Optic Foramen): Passage for the optic nerve.

  • Jugular Foramen: Passage for the jugular vein and cranial nerves.

  • Carotid Canal: Passage for the internal carotid artery.

  • Foramen Lacerum, Ovale, Incisive Canal, Stylomastoid Foramen, External Acoustic Meatus: Various passageways for nerves and vessels.

Foramina of the skull Optic canal/foramina Optic canal/foramina

Mandible Anatomy

The mandible is the largest and strongest bone of the face, forming the lower jaw.

  • Body: Horizontal portion.

  • Ramus (pl. Rami): Vertical portion.

  • Angle: Junction of body and ramus.

  • Coronoid and Condylar Processes: Serve as muscle attachment and articulation points.

  • Mental Foramina: Openings for nerves and vessels.

  • Mandibular Foramen: Passage for the inferior alveolar nerve.

Temporomandibular Joint (TMJ)

The TMJ is the articulation between the condylar process of the mandible and the mandibular fossa of the temporal bone, allowing movement of the jaw.

Sutures of the Skull

Sutures are immovable joints that unite the bones of the skull.

  • Coronal Suture: Between frontal and parietal bones.

  • Sagittal Suture: Between parietal bones.

  • Squamous Suture: Between parietal and temporal bones.

  • Lambdoid Suture: Between parietal and occipital bones.

Fetal and Infant Skull

The fetal and infant skull differs from the adult skull in several ways, allowing for rapid brain growth and flexibility during birth.

  • Fontanelles: Soft spots where bones are not fully fused.

  • Flexible Sutures: Allow for expansion.

  • Large Braincase: Compared to the face.

Fontanelles

  • Anterior Fontanelle

  • Sphenoidal (Anterolateral) Fontanelle

  • Mastoid (Posterolateral) Fontanelle

  • Posterior Fontanelle

Summary Table: Skull Bones and Markings

Bone

Key Markings/Features

Frontal

Supraorbital foramen, frontal sinus

Parietal

Sagittal suture, coronal suture

Occipital

Foramen magnum, occipital condyles, external occipital protuberance

Temporal

Mastoid process, styloid process, external acoustic meatus, mandibular fossa

Sphenoid

Sella turcica, greater/lesser wings, optic canal

Ethmoid

Cribriform plate, crista galli, perpendicular plate, middle nasal concha

Maxilla

Alveolar process, infraorbital foramen, palatine process

Mandible

Body, ramus, angle, coronoid process, condylar process, mental foramen

Labeled skull, cranial bones Labeled skull, cranial bones Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Mastoid, styloid, occipital processes Mastoid, styloid processes Squamous and petrous portions of temporal bone Foramina of the skull Optic canal/foramina Optic canal/foramina Ethmoid bone features Ethmoid bone features Skull processes and fossae Skull processes and fossae Skull processes and fossae Labeled facial bones, anterior view Labeled facial bones, anterior view Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, cranial bones Labeled skull, cranial bones Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Mastoid, styloid, occipital processes Mastoid, styloid processes Squamous and petrous portions of temporal bone Foramina of the skull Optic canal/foramina Optic canal/foramina Ethmoid bone features Ethmoid bone features Skull processes and fossae Skull processes and fossae Skull processes and fossae Labeled facial bones, anterior view Labeled facial bones, anterior view Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, cranial bones Labeled skull, cranial bones Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Mastoid, styloid, occipital processes Mastoid, styloid processes Squamous and petrous portions of temporal bone Foramina of the skull Optic canal/foramina Optic canal/foramina Ethmoid bone features Ethmoid bone features Skull processes and fossae Skull processes and fossae Skull processes and fossae Labeled facial bones, anterior view Labeled facial bones, anterior view Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, cranial bones Labeled skull, cranial bones Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Mastoid, styloid, occipital processes Mastoid, styloid processes Squamous and petrous portions of temporal bone Foramina of the skull Optic canal/foramina Optic canal/foramina Ethmoid bone features Ethmoid bone features Skull processes and fossae Skull processes and fossae Skull processes and fossae Labeled facial bones, anterior view Labeled facial bones, anterior view Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, cranial bones Labeled skull, cranial bones Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Mastoid, styloid, occipital processes Mastoid, styloid processes Squamous and petrous portions of temporal bone Foramina of the skull Optic canal/foramina Optic canal/foramina Ethmoid bone features Ethmoid bone features Skull processes and fossae Skull processes and fossae Skull processes and fossae Labeled facial bones, anterior view Labeled facial bones, anterior view Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, anterior and posterior views Labeled skull, cranial bones Labeled skull, cranial bones Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Sphenoid and ethmoid bone features Mastoid, styloid, occipital processes Mastoid, styloid processes Squamous and petrous portions of temporal bone Foramina of the skull Optic canal/foramina Optic canal/foramina

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