SKULL LANDMARKS

I. CALVARIUM ‑ skull cap. (Snell Fig. 11‑45, 11-46; Atlas Fig. 7.1, 7.2, 7.3)

A. Bones ‑ calvarium consists single Frontal, Sphenoid and Occipital bones and paired Parietal and Temporal bones.

B. Sutures ‑ named fibrous joints that connect bones of calvarium:

1. Coronal suture ‑ between Frontal and Parietal bones

2. Sagittal suture‑ between Parietal bones

3. Lambdoidal suture ‑ between Parietal and Occipital bones

C. Landmarks:

1. Bregma ‑ midpoint of Coronal Suture

2. Lambda ‑ midpoint of Lambdoidal suture

3. Pterion ‑ area of junction of Sphenoid, Temporal, Parietal and Frontal bones.

D. Fontanelles ‑ in infants, bones are further apart and joined by fontanelles; fontanelles permit cranial compression at birth, later cranial growth (Snell Fig. 11‑49):

1. Anterior fontanelle ‑ at Bregma

2. Posterior fontanelle‑ at Lambda

3. Lateral fontanelle‑ at Pterion

E. Internal structure of calvarium (Snell Fig. 11‑26; Atlas Fig. 7.11D)

1. Calvarium consists of hard inner and outer tables of cortical bone surrounding layer of spongy bone (diploe).

2. Diploic veins ‑ course within diploe, connect both to cranial cavity and surface of skull (can transmit infection through emissary veins, see below).

F. Blood supply to calvarium ‑ outer surface receives branches from arteries to scalp (see below); inner surface receives branches from meningeal arteries (coursing immediately below bone).

II. SCALP ‑ layers of skin and connective tissue overlying calvarium. (Atlas Figs. 7.11A, 7.13A)

A. Layers ‑ superficial to deep

1. Skin ‑ with associated hair follicles, sweat glands and sebaceous glands.

2. Connective tissue layer ‑ dense fibrous connective tissue surrounding arteries and nerves.

3. Epicranial Aponeurosis ‑ thin tendinous sheet, tightly attached to skin and connective tissue above; moveable anteriorly and posteriorly; laterally attached to temporal fascia; attached to Frontalis and Occipitalis muscles.

4. Loose Areolar tissue ‑ loosely connects epicranial aponeurosis to periosteum of skull; crossed by emissary veins (see below).

5. Pericranium ‑ periosteum (connective tissue layer) of outer side of calvarium.

Clinical note: Infections can readily spread through loose areolar layer deep to epicranial aponeurosis.

Primitive note: When tribesmen scalp someone, they merely cut along the periphery of the scalp. It is then readily removed between the layers of the epicranial aponeurosis and the loose areolar tissue.

B. Innervation (Atlas Fig. 7.11C)

1. branches of Trigeminal nerve: Supratrochlear and Supraorbital nerves (anterior scalp), Zygomaticotemporal and Auriculotemporal nerves (lateral scalp).

2. Cervical spinal nerves: Lesser Occipital nerves (from ventral ramus of C2) and Greater Occipital nerves (from dorsal ramus of C2) ‑ innervate lateral and posterior scalp.

C. Arterial Supply ‑ very rich (Atlas Fig. 7.11C)

1. branches of Ophthalmic artery: Supratrochlear and Supraorbital arteries (anterior scalp)

2. branches of External Carotid artery ‑ Superficial Temporal artery (to lateral scalp); Posterior auricular artery (scalp above and posterior to external ear); Occipital artery (posterior scalp).

Note: There are extensive anastomoses between arteries to scalp; scalp wounds can bleed profusely.

D. Venous drainage ‑ by veins with same names as arteries; also drain via emissary veins (passing into diploe) into interior of skull. (Atlas Fig. 7.11D)

Note: Infections can spread via emissary veins from scalp to brain.

III. CRANIAL NERVES ‑ brain is bilaterally symmetrical; cortex is connected to spinal cord by brainstem (Atlas Figs. 8.41A, 7.19, 9.1); outflow via cranial nerves; cranial nerves are numbered using Roman numerals:

I. Olfactory - sense of smell

II. Optic - vision

III. Oculomotor - eye muscles

IV. Trochlear - eye muscles

V. Trigeminal

VI. Abducens - eye muscles

VII. Facial

VIII. Vestibulo‑Cochlear - hearing and balance (vestibular apparatus)

IX. Glossopharyngeal

X. Vagus

XI. Accessory

XII. Hypoglossal - muscles of tongue

IV. LANDMARKS AND BONES OF SKULL

A. Views of skull

1. Front of skull (Atlas Fig. 7.1 A and B)

a. Frontal bone – forms forehead, upper margin and roof of orbit

b. Orbit - bones covered in orbit lecture.

c. Zygomatic bones - form cheeks.

d. Maxilla - has sockets for upper teeth (alveolar processes); infraorbital foramen (below orbit).

e. Nasal aperture - covered superiorly by nasal bones.

f. Mandible - alveolar processes for lower teeth; mental foramen (below second pre-molar tooth).

2. Lateral view (Atlas Fig. 7.2 A and B)

a. Zygomatic arch - consists of zygomatic bones and zygomatic processes of maxillary and temporal bones.

b. Temporomandibular joint - joint between head of mandible (upper end of ramus) and temporal bone.

c. Temporal bone - has parts: 1) mastoid process (inferiorly), 2) squamous (flat) part laterally; 3) tympanic part forms anterior side of external auditory meatus (opening of ear); 4) petrous part is inside skull.

d. Parietal, Temporal, Frontal and Sphenoid bones form lateral side of cranial cavity.

3. Posterior view of skull (Atlas Fig. 7.3)

a. Occipital bone - has Superior and Inferior nuchal lines; external occipital protuberance (inion) is raised bump in middle of Superior nuchal line.

4. Base of skull (Atlas Fig. 8.27)

a. Temporal bone - has styloid process for muscle attachment.

b. Occipital bone - has foramen magnum for spinal cord and vertebral arteries; occipital condyles articulate with atlas (C1).

c. Palatine bones and palatine process of maxillary bones form hard palate.

B. Individual bones of skull

1. Sphenoid bone - "core" of skull - forms part of orbit, lateral side of skull, base of skull, parts of all three cranial fossae. (Atlas Fig. 7.1B, 7.2B, 8.27B, 7.17B)

a. Medial and lateral pterygoid plates - processes for muscle attachments.

b. Spine of sphenoid - on inferior side of sphenoid for ligament attachment.

c. Lesser wing of sphenoid - in interior of skull, above superior orbital fissure.

d. Greater wing of sphenoid - extends below superior orbital fissure, extends out laterally.

e. Sella turcica - depression above body of sphenoid (central part).

V. CRANIAL CAVITY ‑ divided into depressions or fossae that are functionally related to parts of brain and facial skeleton. (Atlas Fig. 7.17)

A. Anterior cranial fossa ‑

1. related to roof of nasal cavity (also forms roof of orbit);

2. formed of frontal, ethmoid and sphenoid bones;

3. contains olfactory bulbs and frontal lobes of cortex;

4. foramina ‑ in cribriform plate of ethmoid bone conduct branches (fila olfactoria) of olfactory nerve (nI).

B. Middle cranial fossa ‑

1. related to orbit, nasal cavity and face;

2. formed of sphenoid, temporal and parietal bones;

3. contains pituitary gland, temporal lobes of cortex and cranial nerves from rostral brainstem;

4. foramina ‑ for nerves to orbit (optic nerve and nerves to eye muscles), nasal cavity and face (nII-nVI).

C. Posterior cranial fossa ‑

1. related to face oral cavity, neck;

2. formed of sphenoid, temporal, parietal and occipital bones;

3. contains lower brainstem and cerebellum; petrous part of temporal bone contains cochlea (hearing) and semicircular canals (gravity);

4. foramina ‑ for nerves to face, oral cavity (also taste), muscles of tongue and neck (nVII-nXII); foramen magnum transmits spinal cord and vertebral arteries.