The document describes the anatomy of the anterior, middle, and posterior cranial fossae. It details the boundaries, special features, and foramina of each fossa. Key structures mentioned include the cribriform plate, sella turcica, foramen magnum, optic foramina, and jugular foramen. Clinical significance is noted for fractures involving the cribriform plate which can lead to CSF rhinorrhea and risk of meningitis.

1. Norma Basalis Interna

5. THE ANTERIOR CRANIAL FOSSA

6. The Boundaries of the
Anterior Cranial Fossa
Boundary Bone
Anterior Squamous frontal bone
Laterally Squamous frontal bone
Midline Ethmoid bone

7. The Boundaries of the
Anterior Cranial Fossa
Boundary Bone
Posterior 1.Posterior margin of the lesser wing of
sphenoid
2.Anterior margin of the chiasmatic sulcus

8. Boundary Bone
Floor Orbital plate of frontal
bone,cribriform plate of
ethmoid bone, the crista
galli, and the lesser wing of
sphenoid

9. Special Features of the
Anterior Cranial Fossa
1. Frontal crest
2. Foramen cecum
3. Ethmoidal notch
4. Crista galli
5. Cribriform plate of ethmoid bone
6. Jugum of sphenoid bone
7. Anterior and posterior ethmoidal foramina
8. Grooves for anterior meningeal vessels

10. Frontal crest
- A ridge arising at the termination of the
sagittal sulcus on the cerebral surface of
the frontal bone and ending at the foramen
cecum.
- for anterior attachment of the falx
cerebri

11. Foramen cecum
- foramen varies in size in different
subjects, and is frequently impervious;
when open, it transmits a vein from the
nose to the superior sagittal sinus.

12. Ethmoidal notch
- separates the two orbital plates; it is
quadrilateral, and filled, in the articulated
skull, by the cribriform plate of the
ethmoid.

13. Crista galli
- vertical plate of bone projecting upward
along the midline from the cribriform
plate. It is continuous below with the bony
nasal septum and anchors the anterior end
of the falx cerebri.

14. • Cribriform plate of ethmoid
bone
- is that horizontal part of the ethmoid
bone between the midline and the
frontoethmoidal suture. It is
thin, perforated with many small holes and
easily fractured. It forms the roof of the
nasal cavity on each side.

15. Jugum of sphenoid bone
• a plane surface on the sphenoid bone, in
front of the sella turcica, connecting the
two lesser wings, and forming part of the
anterior cranial fossa.

16. Foramina in the Anterior Cranial
Fossa and their Contents
Name Contents
Cribriform Olfactory nerve fibers
Anterior ethmoid Ant. Ethmoid vessels and nerves
Posterior ethmoid Post. Ethmoid vessels and nerves
Foramen cecum Origin of superior venous sinus

17. Clinical Significance
Fractures in the floor of the anterior cranial
fossa may involve the cribriform plate of
the ethmoid, resulting in leakage of CSF
through the nose (CSF rhinorrhea). CSF
rhinorrhea may be a primary indication of a
cranial base fracture which increases the
risk of meningitis, because an infection
could spread to the meninges from the ear
or nose.

18. THE MIDDLE CRANIAL FOSSA

19. The Boundaries of the
Middle Cranial Fossa
Boundary Bone
Anterior 1. Lesser wings of sphenoid
2. Anterior clinoid process
3. Anterior margin of the
chiasmatic groove

20. Boundary Bones
Posterior 1. Superior angles of the
petrous temporal
2. Dorsum sellae

21. Boundary Bone
Lateral 1. Squamous temporal
2. Petrous temporal
3. Greater wings of sphenoid
4. Parietal bones

22. Boundary Bones
Floor 1. Squamous temporal
2. Petrous temporal
3. Greater wing of sphenoid
4. Sella tursica

23. Special Features of the
Middle Cranial Fossa
1. Sella tursica
2. Posterior clinoid processes
3. Carotid sulcus (groove)
4. Carotid canal
5. Superior orbital
6. fissure
7. Optic foramina
8. Foramen rotundum
9. Foramen ovale
10. Foramen spinosum

24. Special Features of the
Middle Cranial Fossa
11. Foramen lacerum
12. Arcuate emminence
13. Depression for trigeminal ganglion
14. Grooves for the greater and lesser petrosal nerves
15. Groove for the superior petrosal sinus
16. Grooves for the branches of middle meningeal arteries

25. Sella tursica
• A saddlelike prominence on the upper
surface of the sphenoid bone of the skull,
situated in the middle cranial fossa and
dividing it into two halves.
• a depression on the upper surface of the
sphenoid bone, lodging the pituitary gland.

26. Posterior clinoid processes
Posterior angle of the dorsum sellae which
deepen the sella turcica, and give attachment to
the tentorium cerebelli.

27. Carotid sulcus (groove)
it lodges the internal carotid artery and the
cavernous sinus.

28. Carotid canal
is the large circular aperture On the interior
surface of the temporal bone, behind the rough
surface of the apex

29. Superior orbital fissure
lies between the lesser and greater wings
of the sphenoid bone. Through it pass
the branches of the ophthalmic division of
the trigeminal (V1), the oculomotor (III),
trochlear (IV), and abducens (VI) nerves,
and the superior ophthalmic vein.

30. Optic foramina
the optic nerve and ophthalmic artery (with
accompanying sympathetis nerve fibres) into
the orbital cavity.

31. Foramen rotundum
lies in the floor of the middle cranial fossa
at the junction of the body and greater
wing of the sphenoid. It transmits the
maxillary division of the trigeminal nerve
(V2) from the cranial cavity into the
pterygopalatine fossa.

32. Foramen ovale
is a large oval opening in the posterior part of
the greater wing of the sphenoid, half-way
across the floor of the middle cranial fossa. It
transmits the mandibular division of the
trigeminal nerve (V3) from the cranial cavity
into the infratemporal fossa, along with the
lesser petrosal branch of the glossopharyngeal
nerve (IX).

33. Foramen spinosum
• small round hole in the greater wing of the
sphenoid just posterolateral to the foramen
ovale. The middle meningeal branch of the
maxillary artery passes upward through the
foramen into the middle cranial fossa,
accompanied by its postganglionic
sympathetic nerve plexus and the nervus
spinosus, a recurrent meningeal branch of the
mandibular division of the trigeminal nerve.

34. Foramina in the Middle Cranial Fossa and
their Contents
Name Contents
Optic Optic n. and opthalmic a.
Supraorbital Fissure III, IV, VI, opthalmic V nn; sympathetic nn;
opthalmic vv.
Rotundum Maxillary N.
Ovale Mandibular n., meningeal a.
Spinosum Middle meningeal a.
Grooves for greater Greater petrosal n., petrosal br. Middle
petrosal n. meningeal a.
Carotid canal Internal carotid a. and sympathetic nn.

35. THE POSTERIOR CRANIAL FOSSA

36. The Boundaries of the
Posterior Cranial Fossa
Boundary Bone
Anterior 1. Dorsum sellae
2. Basal occipital
3. Crest of petrous temporal
Lateral Parietal bone

37. Boundary Bone
Posterior Squamous occipital bone
Floor Occipital and temporal
bones

38. Special Features of the
Posterior Cranial Fossa
1. Foramen magnum
2. Hypoglossal canal
3. Jugular foramen
4. Internal acoustic
meatus
5. Internal occipital crest
6. Grooves for tansverse
and sigmoid sinuses
7. Mastoid foramen

39. Foramen magnum
the large slightly oval opening in the center of
the floor of the posterior cranial fossa. The
brain stem becomes continuous with the
spinal cord through the foramen, while the
spinal accessory nerves (XI) pass upward
from cervical cord segments into the cranial
cavity.

40. Hypoglossal canal
• pass anterolaterally through the occipital bone
immediately above the occipital
condyles. They transmit the hypoglossal (XII)
nerves.

41. Jugular foramen
• a large, irregular widening of the petrooccipital
suture below the internal auditory meatus. The
sigmoid and inferior petrosal dural venous sinuses
pass through the foramen to join the internal
jugular vein in the jugular fossa. The
glossopharyngeal (IX), vagus (X), and spinal
accessory (XI) nerves also exit the posterior
cranial fossa via the jugular foramen

42. Internal acoustic meatus
(also internal acoustic meatus, internal
auditory canal, and internal acoustic
canal) is a canal in the petrous part of the
temporal bone of the skull that carries
nerves from inside the cranium towards
the middle and inner ear compartments
namely cranial nerve VII and cranial nerve
VIII.

43. Internal occipital crest
gives attachment to the falx cerebelli

44. Mastoid foramen
is a large hole in the posterior border of the
temporal bone. It transmits a vein to the
transverse sinus and a small branch of the
occipital artery to the dura mater.

45. Foramina in the Posterior Cranial Fossa and their
Contents
Name Contents
Magnum Spinal cord, accessory n.,vertebral aa.
Anterior and posterior spinal aa.
Jugular Inf. petrosal and trans. sinuses, meningeal brs.
of occipital and ascending pharyngeal aa.,
IX,X, XI nn.
Hypoglossal XII n., meningeal br. of ascending pharyngeal
a.
Internal auditory VII, VIII nn.; labyrinthine (int. auditory) a.
meatus

46. Other Bones Involved in Norma Basalis
Interna
1. Palatine Bone
2. Ethmoid Bone
3. Sphenoid Bone

47. THE PALATINE BONE

48. • A pair of L-shaped bones, presenting
two main parts that are at right angles
with each other

49. Characteristic Features:
1. Horizontal plate
- forms the opposite
side of the posterior
and lesser portion of
the hard palate.

50. 2. Perpendicular part
- The longer process
found immediately
in front of the
medial pterygoid
plate of sphenoid;
it forms the lateral
wall of the nasal
cavity.

51. Characteristic Features of the Palatine
Bone
3. Pyramidal process
- is directed backwards
and laterally from the
junction of the horizontal
and perpendicular plates.
4. Orbital and sphenoidal
recesses
- two irregular
projections that stand up
from the upper end of the
perpendicular plate.

52. THE ETHMOID BONE

53. • Is irregular in shape, inserted into a notch
between the orbital plates of the frontal
bone, in front of the sphenoid bone. It
forms part of the nasal, cranial, and orbital
cavities.

54. Characteristic Features
1. Cribriform plate
- a thin, horizontal
plate, separating the
nasal cavity from the
cranial cavity. It is
perforated by small
holes for the passage
of the olfactory
nerves.

55. 2. Perpendicular plate
- is an irregular pentagonal plate of bone
forming the upper anterior part of the bony
nasal septum.
- extends upward as the crista galli which
serves for the attachment of the falx cerebri.

56. 3. Ethmoidal labyrinth
- are found on each side of the
perpendicular plate and contain air sinuses –
the anterior, middle, and posterior
ethmoidal paranasal sinuses.

57. The Inferior View

58. The Lateral View

59. The Superior View

60. THE SPHENOID BONE

61. Is found anterior to the occipital bone, between
the two temporal bones at the base of the
skull.

62. CHARACTERISTIC FEATURES OF THE SPHENOID
BONE

63. 1. The Body
- is the central mass in front of the basilar part of the occipital bone.
- saddle-shaped depression superiorly called the sella tursica or the
hypophyseal fossa (location of the pituitary gland or hypophysis
cerebri).
- hollow due to the presence of the sphenoidal paranasal sinuses.

64. 2. Greater wings
- form the floor of the middle cranial fossa and the
side of the skull. It is the location of the “ r o s”
foramens.

65. 3. Lesser wings
- are flattened, triangular plates whose roots
surround the optic foramen.

66. 4. Pterygoid processes
- is made up of the lateral and medial laminae
enclosing the pterygoid fossa. Superior to the
medial pterygoid is the scaphoid fossa while inferior
to it is the pterygoid hamulus.