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Anatomy of the Skull

• Gray's Anatomy for Students, p. 1000-1005
• PC Dikshit Textbook of Forensic Medicine and Toxicology, p. 193

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1. Overview and Regions

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2. The Calvaria (Vault / Roof)

• Frontal bone (anterior)
• Parietal bones (middle - paired)
• Occipital bone (posterior)

Sutures

Internal surface of the calvaria

• The frontal crest (midline ridge) and crista galli are attachment points for the falx cerebri
• The groove for the superior sagittal sinus runs in the midline from front to back
• Granular foveolae are pits that mark arachnoid granulations (involved in CSF reabsorption)
• Grooves for the middle meningeal artery branch laterally from the coronal suture

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3. Bone Structure

• Outer table - thick compact bone (~twice the inner table)
• Diploe - cancellous (spongy) bone containing red bone marrow; begins forming at ~4 years of age
• Inner table - thinner compact bone

• Temporal bone: ~4 mm (thinnest - most susceptible to fracture)
• Frontal and parietal: ~6-10 mm
• Occipital (midline): up to 15 mm (thickest)

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4. The Cranial Cavity and its Three Fossae

Anterior Cranial Fossa

• Cribriform plate of ethmoid - sieve-like plate transmitting olfactory nerve (CN I) fibres from the nasal mucosa to the olfactory bulb
• Crista galli - midline bony projection; attachment for the falx cerebri
• Frontal crest - another falx cerebri attachment
• Foramen cecum - may transmit emissary veins connecting nasal cavity to superior sagittal sinus
• Anterior clinoid processes (lesser wings of sphenoid) - attachment for the tentorium cerebelli
• Boundary with middle fossa: anterior edge of the prechiasmatic sulcus

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Middle Cranial Fossa

• Sella turcica - the "Turkish saddle" in the body of sphenoid; contains the hypophyseal fossa (housing the pituitary gland), bounded anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae
• Posterior clinoid processes - tops of dorsum sellae; attachment for tentorium cerebelli
• Carotid sulcus - groove for the internal carotid artery
• Tegmen tympani - thin bony roof of the middle ear cavity
• Arcuate eminence - rounded bony protrusion overlying the anterior semicircular canal

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Posterior Cranial Fossa

• Foramen magnum - largest foramen in the skull; passage of the spinal cord/brainstem, vertebral arteries, meninges, and spinal roots of the accessory nerve (CN XI)
• Clivus - sloping bone (basilar part of occipital + sphenoid body) ascending from foramen magnum; supports the brainstem
• Internal occipital protuberance - where the transverse sinuses diverge
• Groove for transverse sinus - runs laterally to the internal occipital protuberance
• Groove for sigmoid sinus - S-shaped continuation leading to the jugular foramen

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5. Key Foramina and What Passes Through Them

Anterior Cranial Fossa

Middle Cranial Fossa

Posterior Cranial Fossa

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6. External Skull Base - Key Landmarks

• Occipital condyles - articulate with the atlas (C1)
• Mastoid process - attachment for sternocleidomastoid and other muscles
• Styloid process - attachment for stylohyoid, styloglossus, stylopharyngeus muscles and ligaments
• Stylomastoid foramen - exit of the facial nerve (CN VII) from the skull
• External acoustic meatus - entry to the ear canal
• Mandibular fossa - articulates with the condyle of the mandible (temporomandibular joint)

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7. A Useful 3D Video Resource

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Clinical Relevance

• Temporal bone fractures are most common at the thinnest point and can rupture the middle meningeal artery (inside the epidural space) causing an extradural hematoma
• Cribriform plate fractures cause anosmia and CSF rhinorrhoea
• Foramen magnum herniation (tonsillar herniation/"coning") compresses the brainstem
• Battle's sign (bruising over mastoid) and raccoon eyes (periorbital ecchymosis) indicate base of skull fractures
• The diploe and venous sinuses make the skull a site of haematogenous spread of infection

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Anatomy of the Upper Limb

• Gray's Anatomy for Students, pp. 858-865
• THIEME Atlas of Anatomy - General Anatomy and Musculoskeletal System
• Rosen's Emergency Medicine, Table 43.1

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1. Bones of the Upper Limb

Pectoral Girdle

Arm

• Humerus - long bone with a rounded head articulating with the glenoid cavity; has the greater and lesser tubercles (rotator cuff attachments), the bicipital groove (for the long head of biceps), the deltoid tuberosity, and the medial and lateral epicondyles distally. The surgical neck is where the axillary nerve wraps around.

Forearm

• Radius - lateral bone; has the radial head proximally (articulates with the capitulum of the humerus); the radial styloid process and carpal articular surface distally
• Ulna - medial bone; has the olecranon and coronoid process forming the trochlear notch (articulates with the trochlea of the humerus); the styloid process distally

Wrist and Hand

• 8 Carpal bones (proximal row: scaphoid, lunate, triquetrum, pisiform; distal row: trapezium, trapezoid, capitate, hamate) - mnemonic: She Looks Too Pretty, Try To Catch Her
• 5 Metacarpals
• 14 Phalanges (3 per finger except thumb which has 2)

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2. Joints

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3. Muscles

Shoulder (Rotator Cuff) - "SITS"

Arm - Anterior Compartment (Flexors - Musculocutaneous nerve, C5-C7)

Arm - Posterior Compartment (Extensors - Radial nerve, C6-C8)

Forearm - Anterior Compartment (Flexors/Pronators)

• Superficial: Pronator teres, Flexor carpi radialis, Palmaris longus, Flexor carpi ulnaris
• Intermediate: Flexor digitorum superficialis
• Deep: Flexor digitorum profundus, Flexor pollicis longus, Pronator quadratus

Forearm - Posterior Compartment (Extensors/Supinators)

• Superficial: Brachioradialis, Extensor carpi radialis longus and brevis, Extensor digitorum, Extensor digiti minimi, Extensor carpi ulnaris
• Deep: Supinator, Abductor pollicis longus, Extensor pollicis longus and brevis, Extensor indicis

Hand Intrinsic Muscles

• Thenar muscles (opponens pollicis, abductor pollicis brevis, flexor pollicis brevis) - median nerve
• Hypothenar muscles (opponens digiti minimi, abductor digiti minimi, flexor digiti minimi) - ulnar nerve
• Lumbricals (1 and 2 = median; 3 and 4 = ulnar) - flex MCPs, extend IPs
• Interossei (all = ulnar nerve) - dorsal interossei abduct, palmar interossei adduct fingers ("DAB/PAD")
• Adductor pollicis - ulnar nerve

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4. The Brachial Plexus

Structure: "Robert Taylor Drinks Cold Beer" (Roots, Trunks, Divisions, Cords, Branches)

Branches and Their Cords of Origin

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5. The Five Terminal Nerves

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6. Arterial Supply

• Axillary artery gives off the thoracoacromial, lateral thoracic, and posterior circumflex humeral arteries (the latter accompanies the axillary nerve through the quadrangular space)
• Brachial artery gives off the profunda brachii (deep brachial artery), which accompanies the radial nerve through the spiral groove of the humerus
• At the cubital fossa the brachial artery is medial to the biceps tendon and lateral to the median nerve (from medial to lateral: nerve, artery, tendon)

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7. Venous Drainage

Superficial veins (clinically important for IV access)

• Cephalic vein - runs on the lateral side of the arm, drains into the axillary vein; accessible in the deltopectoral groove
• Basilic vein - runs medially, pierces the deep fascia at mid-arm, joins the brachial vein to form the axillary vein
• Median cubital vein - connects cephalic and basilic in the cubital fossa; the preferred site for venepuncture

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8. Clinical Correlates - Nerve Injuries

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9. Video Resource