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Basis Cranii Externa

An external surface of the skull base or basis cranii externa extends from the maxillary alveolar arch anteriorly – to the external protuberance of the occiput posteriorly. Laterally the base of the skull is bordered by the temporal and infratemporal fossa.

Download JPG image — Bottom view, demonstrating an external surface of the base of the skull. Click an image to switch on comments that are focused on the borders of the base of the skull and on the bony components that build-up the basis cranii. Note that the base of the skull includes some facial skeleton bones, like maxilla and palatine.

The list of terms:
Basis cranii externa – External base of cranium
Fossa temporalis – Temporal fossa
Fossa infratemporalis – Infratemporal fossa
Cavitas nasi – Nasal cavity
Arcus alveolaris maxillae – Maxillary alveolar arch
Palatum osseum – Bony (hard) palate
Choana – Posterior aperture of the nose
Processus pterygoideus – Pterygoid process (of the sphenoid bone)
Pars petrosa – Petrous part (of temporal bone)
Pars tympanica – Tympanic part (of temporal bone)
Processus mastoideus – Mastoid process (of temporal bone)
Clivus
Pars lateralis ossis occipitalis – Lateral part of the occipital bone
Squama occipitalis – Squamous part of occipital bone
Foramen magnum

Download JPG image — Basis cranii externa.

The list of terms:
Arcus alveolaris – Alveolar arch
Juga alveolaria – Alveolar juga (eminences)
Foramen incisivum – Incisive foramen
Canalis incisivus – Incisive canal
Palatum osseum – Bony (hard) palate
Processus palatinus maxillae – Palatine process of maxilla
Lamina horizontalis ossis palatini – Horizontal plate of palatine bone
Sutura palatina mediana – Median palatine suture
Sutura palatina transversa – Transversal palatine suture
Canalis palatinus major – Greater palatine canal
Canalis palatinus minor – Lesser palatine canal
Processus pyramidalis ossis palatini – Pyramidal process of palatine bone
Cavitas nasi – Nasal cavity
Choana – Posterior aperture of the nose
Processus pterygoideus – Pterygoid process
Lamina lateralis processus pterygoidei – Lateral plate of the pterygoid process
Lamina medialis processus pterygoidei – Medial plate of the pterygoid process
Fossa pterygoidea – Pterygoid fossa
Vomer
Foramen ovale
Foramen spinosum
Tuberculum pharyngeum – Pharyngeal tubercle
Foramen lacerum
Tuberculum articulare – Articular tubercle
Fossa mandibularis – Mandibular fossa
Fissura petrotympanica – Petrotympanic (glasserian) fissure
Canalis caroticus – Carotid canal
Fossula petrosa – Petrosal fossula
Canaliculus tympanicus – Tympanic canaliculus
Foramen jugulare – Jugular foramen
Fossa jugularis – Jugular fossa
Foramen stylomastoideum – Stylomastoid foramen
Canalis n. facialis – Canal for the facial nerve
Processus styloideus – Styloid process
Processus mastoideus – Mastoid process
Incisura mastoidea – Mastoid notch
Sulcus a. occipitalis – Groove for occipital artery
Protuberantia occipitalis externa – External occipital protuberance
Linea nuchalis superior – Superior nuchal line
Linea nuchalis inferior – Inferior nuchal line
Crista occipitalis externa – External occipital crest
Foramen magnum

Download JPG image — That illustration shows canals of the base of the skull which usually is more difficult to localize. To find canalis musculotubarius and canalis pterygoideus it is recommended to first localize fossa scaphoidea on the medial plate of the pterygoid process. The cartilage of the pharyngotympanic tube after escaping from the canalis musculotubarius, attaches to the fossa scaphoidea. Follow fossa in the direction toward temporal bone and you will find the entrance to the musculotubarius canal.
Canalis pterygoideus also opens into the basis cranii externa, however, this opening settle deep in the foramen lacerum, at the base of the fossa scaphoidea mentioned above.

The list of terms:
Fossa scaphoidea – Scaphoid fossa
Canalis musculotubarius – Musculotubal canal
Canalis pterygoideus – Pterygoid canal
Canalis condylaris – Condylar canal
Canalis hypoglossalis – Hypoglossal canals