External and internal cranial base

In general, the skull base can be divided into two areas according to the angle of view.

Basis cranii interna

This is the intracranial surface visible after the calva is removed. We are looking at the surface where the brain is located from above. Anatomically, three cranial fossa are distinguished on it.

Division of the interior of the skull

Fossa cranii anterior

Its border extends from the anterior circumference of the skull base to the posterior edge of the lesser wings of the sphenoid bone and the posterior edge of the prechiasmatic sulcus. The surface itself is formed by the partes orbitales and pars nasalis of the frontal bone, the lesser wings of the sphenoid bone, and in the middle the lamina cribrosa of the ethmoidal bone with the crista galli.

The individual structures are listed on the corresponding bones. The passages of this area are:

• canalis opticus – extends from the prechiasmatic sulcus into the orbit, passage for the optic nerve and the ophthalmic artery;
• foramina cribrosa – openings in the lamina cribrosa ossis ethmoidalis for the passage of the olfactory nerves from the cavitas nasi into the cranial cavity;
• vstup foramen ethmoidale anterius – an opening in the cribriform lamina as the end of the orbitocranial canal.
• foramen caecum – the emissary vein may (but may not) pass through this opening.

Fossa cranii media

The middle cranial fossa is defined from the anterior border, which is formed by the posterior border of the anterior fossa, to the posterior border running along the dorsum sellae with the posterior clinoid processes and along the margo superior partis petrosae. The surface of the fossa is formed by the body of the sphenoid bone with the large wings, the anterior surface of the pyramid of the petrous bone and part of the scale of the temporal bone.

The following passages dominate here:

• foramen lacerum – an irregularly shaped opening that is filled with synchondrosis sphenopetrosa during life and appears as an opening during maceration. The canalis caroticus of the pyramid ends here;
• fissura orbitalis superior – passage from the middle cranial fossa into the orbit below the posterior edge of the ala minor of the sphenoid bone and between the ala major, contains:
  • n. oculomotorius (III.);
  • n. trochlearis (IV.);
  • n. abducens (VI.) ;
  • n. ophthalmicus (1st branch of the trigeminal nerve);
  • v. ophthalmica superior;
• foramen rotundum – via the ala major, ventrally, it leads to the maxillary surface into the pterygopalatine fossa of the maxillary nerve (2nd branch of the trigeminal nerve);
• foramen ovale – dorsolaterally located opening leads to the basis cranii externa the mandibular nerve (3rd branch of the trigeminal nerve) with venous connections;
• foramen spinosum – through the greater wing of the sphenoid bone leads from the basis of the skull to the middle cranial the a. meningea media with a branch from the mandibular nerve (3rd branch of the trigeminal nerve) to the dura mater;
• hiatus canalis nervi petrosi majoris et minoris – It opens on the petrous bone for the petrosal nerve major and minor, and for the major nerve it leads from the canal of the facial nerve (zygomaticus nerve).

Fossa cranii posterior

The deepest and largest of the three cranial fossae, it extends from the posterior border of the middle fossa to the posterior border formed by the beginning of the calvaria, into which it subsequently passes. The bones present here include the facies posterior partis petrosae, the intracranial surface of the mastoid process, and the occipital bone.

The main passages of the posterior cranial fossa are:

• porus acusticus internus – facies posterior partis petrosae, leads to the internal acoustic meatus, where the facial nerve canal begins;
  • from the labyrinth of the inner ear, the fibers of the vestibulocochlear nerve (VIII.) enter the skull;
  • the labyrinth, on the other hand, is entered by a. labyrinthi;
• foramen jugulare – an important opening formed by the junction of the incisura of the petrous and occipital bones. On the basis cranii externa, the following passes through:
  • dorsolaterally, the sigmoid sinus to the internal jugular vein;
  • ventromedially the inferior petrosus sinus to the internal jugular vein;
  • outputs of the glossopharyngeal nerve (IX);
  • n. vagus (X.);
  • n. accessorius (XI.).

On the other hand, a.meningea posterior enters the skull to the dura mater.

• through the occipital condyles, the hypoglossal nerve (XII.) passes through the hypoglossal nerve canal

Basis cranii externa

Skull base from below

This area is visible from the bottom of the skull. Its first third is facial, the remaining two thirds contain important structures.

Middle part

The middle part of the external base forms the body of the sphenoid bone with the facies infratemporalis alae majoris and the pterygoid process. The wings of the vomer abut on the rostrum of the sphenoidal bone.

The basic structures are usually those through which blood vessels and nerves pass to or from the cerebral part of the skull. In ala major these are:

• foramen ovale, foramen spinosum, smaller holes;
• crista infratemporalis – elevation separating the external basis of the skull and the temporal fossa;
• spina ossis sphenoidalis located behind the foramen spinosum.

On the pterygoid process, the following depart:

• both laminae of the pterygoid process with the hamulus pterygoideus;
• proc. pyramidalis from the palatine bone;
• the base of the pterygoid process passes dorsoventrally into the pterygopalatine fossa, the pterygoid canal.

Structures of the lower surface of the temporal bone:

• canalis caroticus;
• fossa jugularis;
• fossa mandibularis on the lateral side, contains an articular fossa for the attachment of the mandible and a tubercle, tuberculum articulare, which protrudes in front of the fossa;
• styloid and mastoid processes with stylomastoid foramen for the outlet of the facial nerve canal;
• at the foramen lacerum at the tip of the pyramid and lateral to the carotid canal is the canalis musculotubarius – the auditory tube (Eustachian tube).

Rear part

This part is formed by the occipital bone and contains typical structures for it.

Facial part

Orbit

The orbit (eye socket) is a depression on the facial part of the skull in which the bulbus oculi is located.

Cavitas nasi ossea

It contains the nasal cavity with the nasal conchae.

Fossa temporalis

The temporal fossa is located on the lateral side of the skull and is filled with the temporalis muscle.

Fossa infratemporalis

The infratemporal fossa is the caudal continuation of the temporal fossa.

Fossa pterygopalatina

The pterygopalatine fossa is the medial continuation of the infratemporal fossa and communicates with it through a fissure called the pterygomaxillary fissure.

Links

Related Articles

• Skull
• Skull bones
• Connection on the skull
• Orbit
• Paranasal sinuses

External links

• Mefanet – Hluboké prostory hlavy Fossa pterygopalatina

Used literature

• ČIHÁK, Radomír. Anatomie I. 2. edition. Grada, 2001. 516 pp. pp. 178-200. ISBN 978-80-7169-970-5.

• Incomplete citation of publication. GRIM, Miloš – DRUGA, Rastislav. Základy anatomie, 5.Anatomie krajin těla. Galén, 2008. 119 pp. pp. 96. ISBN 978-80-7262-179-8.