Lab 2R: Cranial & Facial Osteology, Surface Landmarks, & Facial Myology

Course Administration, Lab Policies, and Study Tools

• Lab Schedule and Alternative Sessions:

  • There is no scheduled lab class on Monday. Catch-up & alternative lab sessions are hosted by other TAs on Tuesday, Wednesday, Thursday, and Friday.

• Practical Examination Format:

  • Practical examinations are timed assessment sessions lasting $\le 75\,\text{minutes}$.

  • Students are required to write down explicit anatomical names under pressure.

  • Spelling Rules: University policy strictly enforces spelling accuracy. A single incorrect letter in an anatomical term results in point deductions.

  • Question Phrasing: Exam questions explicitly differentiate between structures: questions will ask specifically for either the name of the bone or the name of the landmark.

  • Examination Models: Practical exams feature uncolored physical skulls. Students must navigate suture lines rather than relying on color coding to identify bone boundaries.

• Anatomical Software Tools:

  • 3D Anatomy: A digital app (available on App Store, MacBook, and Windows) displaying rotatable 3D models of the skull, axial skeleton, and humerus with clickable bone selection.

  • 3D Complete Anatomy: A detailed visualization software option ($\$39$ price). Features include multi-angle inspection (anterior, posterior, superior, inferior, lateral/sagittal), structural isolation, cross-sectional views, fading/hiding of superficial layers to inspect inner cranial structures, and detailed landmark lists.

Anatomical Terminology, Planes, and Structural Divisions

• Anatomical Views and Directional Planes:

  • Superior View: Viewing a structure directly from above (top-down perspective).

  • Inferior View: Viewing a structure directly from below (bottom-up perspective).

  • Anterior View: Frontal perspective of the body or structure.

  • Posterior View: Rear/back perspective of the body or structure.

  • Lateral / Sagittal View: Side perspective of the body or structure.

  • Coronal (Frontal) Plane: A vertical plane dividing the body into anterior (front) and posterior (back) portions.

  • Midsagittal Plane: A vertical plane passing directly through the midline, dividing the body into equal left and right halves.

  • Transverse Plane: A horizontal plane dividing the body into superior (upper) and inferior (lower) portions.

• Skeletal System Classifications:

  • Axial Skeleton: Comprises the central framework of the body, including the skull, vertebral column (spine), rib cage, and sacrum.

  • Appendicular Skeleton: Comprises the bones of the upper and lower limbs, shoulder girdle, and pelvic girdle.

• Anatomical Terminology for Bone Features:

  • Projections (Prominences and Bumps):

  • Process: Any bony prominence or projection.

  • Ramus: An arm-like bar or extension of a bone.

  • Processes Formed for Articulation (Movement Against Adjacent Bones):

  • Condyle: A rounded articular projection.

  • Facet: A smooth, nearly flat articular surface.

  • Head: A prominent, rounded articular end of a bone.

  • Lamina: A thin plate or layer of bone.

  • Neck: A narrowed portion adjacent to the head of a bone.

  • Trochlea: A smooth, pulley-shaped articular surface.

  • Processes Formed for Connective Tissue Attachment (Tendons and Ligaments):

  • Tuberosity: A large, rounded, rough projection or lump.

  • Trochanter: A very large, blunt, irregularly shaped process.

  • Tubercle: A small, rounded projection or process.

  • Spine: A sharp, slender, often pointed projection.

  • Crest: A prominent, narrow ridge of bone.

  • Line: A low, narrow ridge (less prominent than a crest).

  • Depressions:

  • Fossa: A shallow, basin-like depression in a bone.

  • Sulcus: A narrow groove or cleft.

  • Openings and Passageways:

  • Foramen: A large opening or hole through a bone serving as a passageway for spinal cord, nerves, or blood vessels.

  • Canal: A tunnel-like passageway through a bone (smaller than a major foramen).

  • Fissure: A narrow, slit-like opening through a bone.

  • Sinus: A cavity or hollow space within a bone.

Osteology: The Cranial Bones

• The human cranium is composed of $8$ cranial bones that protect the brain:

  • Frontal Bone ($1$): Unpaired bone forming the forehead and superior border of the orbits. Highly visible from anterior and superior views; non-visible from the posterior view.

  • Occipital Bone ($1$): Unpaired bone forming the posterior aspect and base of the skull. Highly visible from posterior and inferior views.

  • Parietal Bones ($2$): Paired bones forming the superior and lateral sides of the cranium. Mnemonic aid: paired central crown plates.

  • Temporal Bones ($2$): Paired bones forming the lower lateral walls and base of the skull. Mnemonic aid: "tempo" or "tempura".

  • Sphenoid Bone ($1$): Unpaired, complex bat-shaped or butterfly-shaped bone stretching across the middle floor of the cranial cavity. Key diagnostic landmark visible superiorly inside the opened skull floor, anteriorly within the deep posterior orbit, and laterally on the skull surface.

  • Ethmoid Bone ($1$): Unpaired, complex cuboidal bone situated anterior to the sphenoid bone. Forms part of the anterior cranial fossa, the medial wall of the orbit, and the superior structures of the nasal cavity.

Osteology: The Facial Bones

• The facial skeleton is composed of $14$ facial bones:

  • Maxillary Bones / Maxillae ($2$): Paired upper jawbones forming the central facial structure, inferior orbital borders, and the anterior two-thirds of the hard palate.

  • Mandible ($1$): Unpaired lower jawbone; the largest and strongest bone of the face.

  • Lacrimal Bones ($2$): Paired, tiny fingernail-sized bones situated in the anterior-medial wall of each orbit (associated with tear ducts/lacrimal apparatus).

  • Zygomatic Bones ($2$): Paired cheekbones forming the lateral walls and floors of the orbits.

  • Nasal Bones ($2$): Paired small rectangular bones forming the bridge of the nose.

  • Palatine Bones ($2$): Paired L-shaped bones forming the posterior one-third of the hard palate (roof of the mouth) and part of the nasal cavity floor.

  • Inferior Nasal Conchae ($2$): Paired curved bones projecting medially from the lateral walls of the lower nasal cavity (singular: concha, plural: conchae).

  • Vomer ($1$): Unpaired, thin plow-shaped bone situated along the midline of the nasal cavity, forming the inferior and posterior portion of the nasal septum.

Skull Landmarks and Features

• Sutures: Fibrous, immovable joint lines connecting adjacent cranial bones.

• Foramen Magnum: The major, large opening in the inferior aspect of the occipital bone that transmits the spinal cord/brainstem. Visible from inferior and deep anterior perspectives.

• External Acoustic Canal (External Auditory Meatus): A canal opening on the lateral aspect of the temporal bone leading into the internal ear structures.

• Zygomatic Arch Components:

  • Temporal Process of Zygomatic Bone: A posterior projection of the zygomatic bone that articulates with the temporal bone.

  • Zygomatic Process of Temporal Bone: An anterior projection of the temporal bone that articulates with the zygomatic bone.

• Mastoid Process: A prominent, rounded bony projection on the inferior/posterior portion of the temporal bone located posterior and medial to the external acoustic canal (palpable behind the earlobe).

• Orbital Rim: The continuous outer bony margin/edge forming the rim of the orbit (eye socket).

• Hard Palate: Bony roof of the mouth visible from the inferior view, formed conjointly by the maxillae (anterior $2/3$) and the palatine bones (posterior $1/3$).

• Mandibular Landmarks:

  • Ramus of Mandible: The vertical posterior branch on each side of the lower jaw.

  • Body of Mandible: The curved horizontal portion forming the chin and tooth sockets.

• External Occipital Protuberance: A prominent midline bony bump on the outer surface of the occipital bone at the posterior base of the skull.

Myology: Functional Principles and Muscle Fiber Architecture

• Structural Classifications of Muscle Fibers:

  • Unipennate: Muscle fascicles insert into only one side of the tendon.

  • Bipennate: Muscle fascicles insert into both sides of a central tendon (e.g., rectus femoris muscle, which acts to produce knee extension).

  • Multipennate / Convergent: Muscle fascicles converge from a broad origin to a single attachment point (e.g., deltoid muscle, which possesses anterior, medial, and posterior heads to perform shoulder abduction and flexion).

  • Circular: Concentric ring arrangement of muscle fibers surrounding external body orifices (e.g., orbicularis sphincter muscles).

• Functional Muscle Classifications:

  • Agonist (Prime Mover): The primary muscle directly responsible for producing a specific anatomical action.

  • Synergist: A muscle that assists the prime mover in performing an action or stabilizes intermediate joints.

  • Antagonist: A muscle that directly opposes or reverses the movement of a prime mover (e.g., the triceps brachii acts as the antagonist to the biceps brachii during elbow flexion; the hamstrings act as the antagonist to the rectus femoris during knee extension).

  • Origin: The stationary, unmovable point of muscle attachment (~$99\%$ of cases).

  • Insertion: The movable point of muscle attachment that pulls toward the origin during contraction.

Myology: Muscles of the Head and Face

• Orbicularis Oculi:

  • Fiber Pattern: Circular muscle encircling the orbit.

  • Action: Closes the eye (squinting, blinking, winking).

• Orbicularis Oris:

  • Fiber Pattern: Circular muscle encircling the mouth.

  • Action: Constricts the oral opening; closes and puckers lips.

• Platysma:

  • Location: Broad, thin, flat muscle covering the anterior neck.

  • Depth: Most superficial muscle layer of the neck region.

  • Action: Depresses the mandible, pulls lower lip down, and tenses skin of the neck.

• Temporalis:

  • Location: Fan-shaped muscle overlying the temporal bone on the lateral side of the skull.

  • Action: Elevates the mandible (closes jaw during mastication/chewing).

• Buccinator:

  • Location: Deep lateral cheek muscle forming the wall of the cheek.

  • Action: Compresses the cheek against the teeth (used during whistling, blowing, chewing, and kissing actions).

• Masseter:

  • Location: Powerful, thick muscle covering the lateral surface of the mandibular ramus.

  • Action: Elevates the mandible (closes jaw during mastication/chewing).