Osteology

Sphenoid

• A complex bone comprising part of the skull base:

• Embryologically: the skull base begins as cartilaginous precursors which then ossify, including the sphenoid

• Note: the other bones of the orbit form by membranous ossification (no cartilaginous precursor)

Components 

• Body: containing the deep depression of the sella turcica
• Lesser wing
• Greater wing
• Pterygoid processes with pterygoid hamulus on the ends
• Foramen ovale which transmits numerous structures (see later)
• The optic canal passes through the lesser wing
• The superior orbital fissure is formed between the lesser and greater wings
• The foramen rotundum passes through the pterygoid process
• Foramen spinosum transmits the middle meningeal artery
• The small pterygoid canal lies medially

Temporal

• Squamous part connects with the greater wing of the sphenoid and parietal bones
• Zygomatic process forms part of the zygomatic arch
• Petrous part contains the middle ear, labyrinth and the carotid canal
• Mastoid part connects with the parietal and occipital bones and contains air cells.
• This contains the stylomastoid foramen, which transmits the facial nerve
• Tympanic part forms the wall of the external auditory meatus

Maxilla

• So-called membranous bone (compare with sphenoid above)
• Forms part of the orbital floor, lateral wall of the nose and hard palate
• Contains the pyramidal maxillary sinus
• The roof of the sinus is indented by the infraorbital canal
• The sinus drains the middle meatus of the nasal cavity

Connections from cranial fossa (and contents)

Middle cranial fossa

• Foramen ovale to the infratemporal fossa
• OVALE
• V3: mandibular division of trigeminal
• Accessory meningeal artery
• Lesser petrosal nerve
• Emissary vein
• Foramen spinosum connects to infratemporal fossa
• Middle meningeal artery and vein
• Meningeal branch of the mandibular nerve
• Foramen lacerum

• Parasympathetic fibres via the greater petrosal nerve travelling to the pterygopalatine ganglion

• The ICA passes over the surface
• Foraman rotundum
• Maxillary nerve 
• Small veins of the cavernous sinus
• Pterygoid canal
• Deep petrosal nerve
• Greater petrosal nerve
• Stylomastoid foramen (part of the temporal bone)
• Facial nerve (excluding chorda tympani)
• Pterygotympanic fissure
• Transmits the chorda tympani to the infratemporal fossa

Posterior cranial fossa

• Jugular foramen (formed by petrous temporal and occipital bones)
• Glossopharyngeal
• Vagus
• Accessory (cranial part)
• Internal jugular vein
• Foramen magnum
• Accessory (spinal part)
• Hypoglossal canal
• Hypoglossal nerve

Cervical vertebrae

• Seven in total
• Atlas and axis (C1 and C2) are unique
• C7 is unique
• Transverse process occasionally enlarged to form a so-called ‘cervical rib’
• C3-C6 are ‘typical’
• Triangular shaped canal
• Bifid spinal processes
• Kidney shaped body
• Small transverse processes
• Foramen transversarium is within the transverse processes of all vertebrae

Infratemporal fossa

• Found behind the maxilla and the zygomatic arch
• Roof: greater wing of sphenoid and squamous part of the temporal bone
• Medial wall: lateral pterygoid plate
• Anterior wall: maxilla
• Posterior wall: styloid apparatus
• Lateral wall: mandibular ramus
• Middle meningeal artery exits the fossa through the foramen spinosum

• Maxillary artery leaves via the pterygomaxillary fissure and enters the pterygopalatine fossa

• Mandibular division of the trigeminal enters through the foramen ovale

• Otic ganglion lies in the fossa and immediately below the foramen ovale: receives preganglionic parasympathetic supply from the lesser petrosal nerve (component of the glossopharyngeal bound for the parotid gland) and communicates with the facial nerve

Trivia: the vomer (which forms the nasal septum) and the mandible are the only unpaired facial bones.