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Mandible and Bones of the Skull - Physiotherapy Notes

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1. Overview of the Skull

Key exam point: The skull has 3 pairs of synovial joints: 2x temporomandibular joints (TMJs) + 3 ossicles on each side (malleus-incus, incus-stapes joints in the middle ear).

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2. Anterior View of the Skull

Frontal Bone

• Forms the forehead and superior rim of each orbit
• Superciliary arches - raised ridges above orbital rim (more pronounced in males)
• Glabella - small depression between the superciliary arches
• Supra-orbital foramen/notch - transmits supra-orbital nerve and vessels (visible in medial part of superior orbital rim)
• Zygomatic process of frontal bone - forms the upper lateral rim of the orbit

Nasal Bones

• Two small paired bones forming the bridge of the nose

Zygomatic Bone

• Cheekbone; forms lateral orbital rim and zygomatic arch

Maxilla (Paired)

• Forms upper jaw
• Contains the alveolar process (bears upper teeth)
• Infra-orbital foramen - transmits infra-orbital nerve and vessels, below the orbital margin
• Anterior nasal spine - midline projection at the base of the nasal aperture
• Frontal process of maxilla - forms medial orbital margin

Inferior Nasal Concha

• Scroll-like bone visible within the nasal (piriform) aperture

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3. Lateral View of the Skull

Bones of the Lateral Calvaria

• Frontal → Parietal at the coronal suture
• Parietal → Occipital at the lambdoid suture
• Frontal → Greater wing of sphenoid → Parietal at the sphenoparietal suture
• Sphenoid → Temporal at the sphenosquamous suture
• Temporal → Parietal at the squamous suture

Key Landmark - Pterion

Temporal Bone

• Has squamous, mastoid, tympanic, and petrous parts
• Mastoid process - prominent posterior projection; attachment for sternocleidomastoid and other neck muscles
• Styloid process - thin projection, attachment for stylohyoid, styloglossus, stylopharyngeus
• Zygomatic process - forms the zygomatic arch with the temporal process of the zygomatic bone
• Asterion - junction of occipital, parietal, and temporal bones (posteriorly)

Sutures - Summary Table

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4. Posterior View of the Skull

Occipital Bone

• Main bone of the posterior skull
• Articulates with parietal bones at the lambdoid suture and temporal bones at the occipitomastoid sutures
• Wormian (sutural) bones - small island bones along the lambdoid suture
• External occipital protuberance - midline bony bump; the most prominent point is called the inion
• Superior nuchal lines - curved ridges extending laterally from the protuberance; muscle attachment
• Inferior nuchal lines - ~2.5 cm below superior lines; further muscle attachment
• External occipital crest - ridge running from protuberance toward the foramen magnum

Temporal Bones (Posterior View)

• Mastoid process is the prominent feature
• Mastoid notch - on the inferomedial border of the mastoid process; attachment for posterior belly of digastric muscle

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5. Superior View of the Skull (Calvaria/Calva)

• Coronal suture: Frontal ↔ Parietal
• Sagittal suture: Left Parietal ↔ Right Parietal (midline)
• Lambdoid suture: Parietal ↔ Occipital
• Bregma - junction of sagittal and coronal sutures (site of anterior fontanelle in newborns)
• Lambda - junction of sagittal and lambdoid sutures (site of posterior fontanelle in newborns)
• Parietal foramina - paired small foramina lateral to sagittal suture posteriorly

Structure of Calvaria (Diploe)

1. External table - dense compact bone
2. Diploë - spongy cancellous bone layer (contains red bone marrow)
3. Internal table - dense compact bone

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6. Base of Skull - Inferior View

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7. The Mandible - Detailed

Parts of the Mandible

External (Lateral) Surface Features

• Base of mandible - lower border of body
• Alveolar part - upper part of body, bears the teeth; resorbed when teeth are removed
• Mental protuberance - midline swelling where the two halves meet (the "chin")
• Mental tubercles - slight bumps just lateral to mental protuberance
• Mental foramen - midway between upper alveolar border and lower base of mandible; transmits mental nerve and vessels (branch of inferior alveolar nerve/artery)
• Oblique line - ridge from the front of the ramus onto the body; attachment for muscles that depress the lower lip

Internal (Medial) Surface Features

• Mandibular symphysis - site of fusion; visible as a small vertical ridge externally
• Superior and inferior mental spines (genial spines) - two pairs of small spines posterior to symphysis; attachments for genioglossus (superior) and geniohyoid (inferior) muscles
• Mylohyoid line - raised ridge running posterosuperiorly from midline; attachment for mylohyoid muscle (floor of mouth)
• Sublingual fossa - shallow depression above anterior 1/3 of mylohyoid line; houses sublingual salivary gland
• Submandibular fossa - depression below posterior 2/3 of mylohyoid line; houses submandibular salivary gland
• Retromolar triangle - small triangular area posterior to last molar; attachment for pterygomandibular raphe
• Shallow groove for lingual nerve - between last molar tooth and mylohyoid line

Ramus Features

• Mandibular foramen - large foramen on medial surface of ramus; transmits inferior alveolar nerve and vessels into the inferior alveolar canal
• Lingula - small bony projection at the anterior edge of mandibular foramen; attachment for sphenomandibular ligament

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8. Key Foramina and Their Contents (Exam Table)

Remember the "3 on a line" rule: Supra-orbital, infra-orbital, and mental foramina are roughly vertically aligned - useful clinically for nerve blocks.

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9. Fontanelles (Physiotherapy and Developmental Context)

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10. Physiotherapy Clinical Relevance

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11. Muscles Attaching to the Mandible (Physiotherapy Muscle Chart)

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Quick Revision Summary

• 22 skull bones (excl. ossicles): 1 frontal, 2 parietal, 2 temporal, 1 occipital, 1 sphenoid, 1 ethmoid + facial bones
• Only movable skull bone = mandible
• Sutures = fibrous immovable joints; TMJ = only synovial joint involving skull + mandible
• Pterion = thinnest skull region, H-junction of 4 bones, overlies middle meningeal artery
• Bregma = anterior fontanelle site; Lambda = posterior fontanelle site
• Mandible parts: body (alveolar + base), ramus, angle, coronoid process, condylar process
• Mental foramen = on body; Mandibular foramen = on ramus (medial)
• Mylohyoid line = important oral floor muscle attachment on mandible's medial surface
• Gray's Anatomy for Students, pp. 979-998, 1229-1231