Another bit of information about the dura. In certain areas, the meningeal layer of the dura splits away from the fibrous layer forming intracranial venous sinuses. When the meningeal layer pulls away, double layers of dura extend into the cranial cavity separating the left and right cerebral hemispheres from one another forming the falx cerebri. Another double layer of meningeal dura is formed between the occipital pole of the brain and the cerebellum and is called the tentorium cerebelli. Now you are ready to identify these various structures within the cranial cavity.

First, identify the various parts of the dura shown below.

Parts of the dura:

	falx cerebri (1)
	tentorium cerebelli (2)
	falx cerebelli (6)

Superior view

Sagittal view

Look for and name the venous sinuses. The superior sagittal sinus is located in the attached margin of the falx cerebri. The inferior sagittal sinus is located in the free margin of the falx cerebri. The transverse sinus is in the attached border of the tentorium cerebelli. The superior petrosal sinus is in the attached margin of the tentorium cerebelli where it attaches to the upper border of the petrous temporal bone.

Cranial intravenous sinuses:

1 sphenoparietal
2 cavernous
3 inferior petrosal
4 transverse
5 sigmoid
6 superior petrosal >br> 7 straight
8 superior sagittal

It might be useful at some point in your education to understand the relationship of the cranial cavity to the base of the brain. This is shown, color coded, in the following images.

Compare the base of the brain with the skull adjacent to it and you can see which parts of the brain are associated with which bones of the skull.
1 frontal 2 ethmoid 3 sphenoid 4 temporal 5 parietal 6 occipital

The images below demonstrate how the cranial nerves appear with the dura intact and then the foramina that the nerves pass through to leave the cranial cavity.

Memorize the cranial nerves;
I Olfactory (cribriform plate)(special sensory)
II Optic (optic foramen)(special sensory)
III Oculomotor (superior orbital fissure)(motor and autonomic)
IV Trochlear (superior orbital fissure)(motor)
V Trigeminal (motor & general sensory)

V1 (superior orbital fissure)(general sensory)

V2 (foramen rotundum)(general sensory)

V3 (foramen ovale)(general sensory and motor)
VI Abducens (motor)
VII Facial (motor, special sensory, and autonomic)
VIII Vestibulocochlear (special sensory)
IX Glossopharyngeal (motor, special & general sensory and autonomic)
X Vagus (motor, general & special sensory and autonomic)
XI Spinal accessory (motor)
XII Hypoglossal (motor)

This diagram points out the structures found within the cavernous sinus and within its walls

In the walls:

	1 oculomotor
	2 trochlear
	4 V1
	5 V2

Within:

	3 abducens
	6 autonomic plexus
	7 internal carotid artery

8 pituitary gland
9 body of sphenoid bone

List of Items to be able to identify for this lesson

Calvaria

compact bone

spongy bone

diploie

arachnoid granulations

sulcus for superior sagittal sinus

Bones forming floor and sides of cranial cavity

frontal

ethmoid

sphenoid

lesser wing

anterior clinoid processes

body

hypophyseal fossa

dorsum sellae

greater wings of sphenoid

temporal

squamous part

petrous part

parietal

occipital

Parts of dura mater

falx cerebri

falx cerebelli

tentorium cerebelli

diaphragma selli

Venous sinuses

superior sagittal

inferior sagittal

straight

sphenoparietal

superior petrosal

inferior petrosal

transverse

sigmoid

cavernous

Cranial nerves and foramen of exit from cranial cavity

I olfactory cribriform plate of
ethmoid

II optic optic foramen

III oculomotor superior orbital
fissure

IV trochlear superior orbital
fissure

V trigeminal

V1 ophthalmic division
superior orbital fissure

V2 maxillary division foramen
rotundum

V3 mandibular division
foramen ovale

VI abducens superior orbital
fissure

VII facial internal auditory (or
acoustic) meatus

VIII vestibulocochlear internal
auditory (or acoustic) meatus

IX glossopharyngeal jugular
foramen

X vagus jugular foramen

XI spinal accessory foramen
magnum and jugular foramen

XII hypoglossal hypoglossal
foramen

Cavernous Sinus

Structures in the wall:

oculomotor nerve

trochlear nerve

ophthalmic division of
trigeminal nerve

maxillary division of trigeminal
nerve (sometimes)

Structures within the sinus:

abducens nerve

internal carotid artery

carotid sympathetic plexus

The Orbit

The orbit can be studied from the front or from the top. In most dissection laboratories, the roof of the orbit is broken away and the orbital structures are cleaned and studied. First lets take a look at the bones and foramina of the orbit since these may be referred to later during the lesson.

Bones of the Orbit Viewed From the Front

In the images below, you are looking at the left orbit and the medial side of the orbit is to the left.

Bones

frontal
zygomatic
maxilla
lacrimal
ethmoid
greater & lesser wing of sphenoid
palatine

Orbital foramina

optic
superior orbital fissure
inferior orbital fissure
posterior ethmoid
anterior ethmoid

Structures that pass through the foramina are:

	optic nerve and ophthalmic artery through the optic foramen
	oculomotor, trochlear, V1 and abducens through the superior orbital fissure
	anterior & posterior ethmoid nerves through the anterior & posterior ethmoid foramina
	infraorbital nerve through the inferior orbital fissure The rest of the orbital cavity is filled with orbital fat, muscles of the eyeball, the eyeball, the lacrimal gland, ophthalmic artery and its branches, and the ophthalmic vein and its tributaries. We will start examining the contents of the orbit from above down.

Contents of the Right Orbit from Top to Bottom

When the frontal bone is chipped away and the orbit is entered, the first thing you will see is a connective tissue structure enclosing the eyeball and its muscles, vessels and nerves, the periorbita. This is a glistening structure.

After the periorbita is stripped away, you will then encounter a large amount of fat filling the structures in the orbit. Once this fat is cleaned away, you will find the following structures:

	trochlear nerve (T)
	frontal nerve (F) supraorbital nerve (SO) supra trochlear nerve (ST)
	lacrimal nerve (L)
	lacrimal gland (Lac)
	levator palpebrae superioris (LPS)

After these structures are identified, the levator palpebrae superioris is reflected forward and the next layer of items is revealed.

In this layer, we see three muscles:

	superior oblique (SO)
	superior rectus (SR)
	lateral rectus (LR)

and the nasociliary nerve (nc) anterior ethmoid (ae)
posterior ethmoid (pe)

By reflecting the superior rectus and the superior oblique, we can now examine the eyeball itself and adjacent items:

	optic nerve (ON)
	short ciliary nerves (sc)
	medial rectus muscle (MR)
	ophthalmic artery (red)
	superior ophthalmic vein (blue)
	eyeball

Reflection of the eyeball and optic nerves brings us to the lowest items in the orbit:

	ophthalmic artery (OA)
	ophthalmic vein (OV)
	ciliary ganglion (cg)
	inferior division of oculomotor nerve (ION) (with cg attached)
	inferior rectus muscle (IR)
	inferior oblique muscle (IO)

Finally, we reach the orbital floor which is made up of the zygomatic and maxillary bones. A sulcus can be seen in the maxillary bone and this holds the infraorbital nerve (ION). The zygomatic bone has a zygomatic foramen which accepts the zygomatic branch of the infraorbital nerve (Z). The infraorbital nerve is a branch of the maxillary division (V2) of the trigeminal nerve. It enters the orbit through the inferior orbital fissure.

Once the structures in the orbit are learned, you should then try to understand how the muscles act on the eye to move it. This knowledge is necessary in clinical situations when you examine the eye during a full physical examination or after head injuries. In order to fully understand the movements of the eyeball you should realize that the eyeball moves around three axes: (1) vertical, (2) horizontal and (3) anteroposterior. Movements around the vertical axis are abduction and adduction, around the horizontal axis, elevation and depression and around the anteroposterior axis, medial and lateral rotation. This last movement usually requires the use of special equipment to see it, so we won't consider it at this time.

Movements of the Right Eye as Viewed from Above

In the adjacent figures, we point out the muscles that perform the various movements of the eye (The 3 axes are in black):

Elevation is movement of the eye around the horizontal axis so that it is looking upward. This movement is performed by a pair of muscles:

	superior rectus (SR)
	inferior oblique (IO)

Depression is movement of the eye around the horizontal axis so that it is looking downward. This movement if performed by a pair of muscles:

	inferior rectus (IR)
	superior oblique (SO)

adduction is movement of the eye around the vertical axis so that it is looking toward the nose. There is only one muscle that originates this movement.

medial rectus (MR)

abduction is movement of the eye around the vertical axis so that it is looking laterally. The muscles that perform this action are:

	lateral rectus (LR)
	superior oblique (SO)
	inferior oblique (IO)
	superior rectus (SR)
	inferior rectus (IR)

Muscle	Action	Nerve Supply
levator palpebrae superioris	raises the eyelid	upper division of oculomotor nerve (III)
superior rectus	elevates and abducts eyeball	upper division of oculomotor nerve (III)
superior oblique	depresses and abducts eyeball	trochlear nerve (IV)
medial rectus	adducts the eyeball	lower division of oculomotor nerve (III)
lateral rectus	abducts the eyeball	abducens nerve (VI)
inferior rectus	depresses and abducts eyeball	lower division of oculomotor nerve (III)
inferior oblique	elevates and abducts eyeball	lower division of oculomotor nerve III)

AFGALALY محمد عبد الفتاح جلال

Cranial Cavity

Bones and parts of bones of the cranial cavity

First, identify the various parts of the dura shown below.

List of Items to be able to identify for this lesson

The Orbit

Bones of the Orbit Viewed From the Front

Contents of the Right Orbit from Top to Bottom

Movements of the Right Eye as Viewed from Above

Table of Muscles of the Orbit and Their Nerve Supply and Actions

Examination of Individual Muscles

Arteries of the Orbit

The Ear

List of items to identify in this lesson