ANATOMY OF VISION I ^*

An Audiotutorial Overview of the Human Brain's
VISUAL SYSTEM

Paul Pietsch, PhD,
Professor Emeritus,
School of Optometry
Indiana University

SOUND CONTROL

Tape A

{42-min tape}
You get two tapes on this lesson, Doc.
When, the man starts in about flipping the tape and a "friendly" quiz, get ready to go to Tape B -- a real short one but with some worthwhile goodies on it.
But that's down the line, toward the end of Tape A.
(Note: there's a blank space a short distance into A that lasts around a minute or so. Ergo, as they say on Strawberry Hill, keep your knickers dry 'til the sound starts up again. )
Before you get going, though, let me give you a few tips about pictures we'll use as substitutes for stuff you probably don't have on your tray (e.g., pickled brains, the man's head in a box and Dr. Netter's drawings):

Instead of sheep brains (no French cuisine on this trip, Doc!) we'll use photos of the human brain. To take a quick look at them, click here .
We've also put photos showing replica models of human heads. To see them, click here.
And we give you a special series on a part of the visual pathways called the optic radiations -- dissections from the human brain collection of the Indiana University School of Optometry.
You'll also find pictures of the occipital lobe (aka, optic lobe); and important map areas (Brodmann) as well as what are called eye fields).
Colliculi? Latin for bumps, Doc! (The singular is colliculus.) When the man starts talking about colliculi don't get a spastic colon. Instead, click here! (They're useful surface markers for nuclei that help move the eyes.)
On the tapes, you'll hear much about slides. Those slides that are essential for studying vision, are here; the numbers are the same as on the tapes. And there's a special Slide Control Panel to help you navigate when the time comes. (We'll also supply you with a hyperlink to the entire slide set, when the time comes.)
On the subject of slides, the most important of all, to quote the man, is "Slide Number 20," (which you can bring into your window with a click here).
Finally, for those who are reviewing for national or state boards or licensing exams, etc. (or if you're just a worry wart about everything you study), there's a check list, arranged by subdivisions of the brain.
Good luck!
{back to sound control}
Tape B

{7-min tape}

Sheep Brain Substitutes (human brains) (back to Cranky's suggestions)

Optic Nerve (stump)
Optic Chiasm
Optic Tract
Tuber Cinerium (of the hypothalamus)
m, Mammillary Bodies (also hypothalamus)
For a closer view, click here.

See what you can identify without the labels, Doc.

CLOSER VIEW:

{back to the previous picture}

INSIDE THE HUMAN HEAD
(back to Cranky's suggestions)

This is a sagittal section of the head, enough off-line to show midline structures such as the pineal body, the pituitary gland and stalk and the falx cerebri. The falx is an extension of the dura mater (the thick, outermost of the three meninges), in most places applied to the inner surface of the cranium. (Another prolongation of dura mater, the tent-like tentorium cerebelli can be seen by clicking here.) The falx extends down into the longitudinal fissure, between the cerebral hemispheres, almost to the corpus callosum.
The falx is a parenthetical, if conspicuous, entity here. But the big deal for us, at present, is the intracranial segment of the optic nerve, en route to the back of the orbit. To appreciate the relationship in situ of the visual pathways and the pituitary gland click here.
For a closer look at the structures in question, click here.

To return to slide 19, click here.

Optic chiasm in situ:
{To get back to the sagittal section of the head click here!}

Optic nerve and pituitary stalk (click to get back to wider view):

TENTORIUM CEREBELLI:

Here's the tentorium cerebelli. Sandwiched between the cerebellum and the occipital lobe of the cerebrum in the intact cranium, its name comes from its tent-like appearance over the posterior cranial fossa where the cerebellium normally lies.
(These photos of the inside of human cranium are of replicas of cadavers' heads. In principle, the model is made much like molding Jello. An impression is made of the surface the given dissection and a cast produced from it; the liquid form of a rubbery plastic is poured into the cast and then polymerized into a solid with the same surface features as the dissected specimen.
{To get back to the sagittal section of the head click here!}

SPECIAL SERIES ON THE OPTIC RADIATIONS

(back to Cranky's suggestions)

This section is arranged in three parts:

Five views of a dissection to display the optic radiations from different perspectives.
An MRI of the brain in transverse section [click].
A second dissection of the optic radiations.

Five Views (of dissection 1):

2
(Top-right view of 1)

3
(Left, lateral view of 1):

That big pit is where the lenticular nucleus was scouped out to expose the lateral side of the internal capsule. Most of the outside of the occipital lobe was shaved away to expose the optic radiations. (The frontal pole points left and the occipital pole, still there, points right.)
What can we take away from a picture like this? For one thing, Doc, the optic radiations, like the internal capsule, the corpus callosum, or certain so-called 'fasciculi' are part of the cerebral hemisphere's massive white matter, (aka, medullary substance); the cortex, recall, is gray matter (location of the neuronal cell bodies). What makes for 'whiteness,' incidentally, is the suet-like myelin sheath around each of the millions and millions of fibers. The cortex, on the surface of the cerebrum, has many, many fibers too, but no myelin.
Functions? White matter communicates, gray matter processes ('thinks').
For a closer look at view 3 click here.

4 (Closer view of the perspective in 3):

{back to View 1}

5 (View of 4 from the other side.)

Note the lips of the calcarine fissure, Doc! (Anatomists actually call them 'lips,' believe it or not (some do, anyway). In this picture, we're looking at the primary visual cortex (aka area 17, or striate cortex) -- cuneate gyrus above, lingual gyrus below. You've got one of those things inside your own head, Doc!

{back to View 1 of dissection} To see specimen 2, click here!

(back to Cranky's suggestions)

MRI
{back to View 1}

ANOTHER DISSECTION OF THE OPTIC RADIATIONS

Note: Meyer's temporal loop belongs to the optic radiations. These are fibers from neurons in the lower, outer part of the LGB (lateral geniculate body); the fibers in question first swoop forward, almost to the uncus, to get around the inferior (temporal) horn of the lateral ventrial, then arc back into the occipital lobe, there to plug into the anterior one-third of the lower lip of the calcarine fissure. The significance of the latter fact will be taken up in a later lesson.

(back to Cranky's suggestions)

CEREBRAL CORTEX: VISUAL PARTS
(back to Cranky's suggestions)

BRODMANN MAP OF THE MEDIAL ASPECT OF THE
OCCIPITAL LOBE:

EYE FIELDS:

The frontal eye fields (the known parts, anyway) are in a stamp-sized zone at the posterior end of the middle frontal gyri (in both hemsipheres). The latter is part of Brodmann's Area 8. Frontal eye fields play a major role in stepwise and voluntary eye movements known as saccades. The occipital eye fields -- in areas 18 and 19 -- are used in involuntary, smooth pursuit movements of the eyes as in tacking a hornet or a frisbee (or Superman). This specimen came from a commercial supplier with those blue markings already there, and they wouldn't rub off. Was somebody trying to outline the central fissure (sulcus)? Maybe, maybe not!
Anyway, a central fissure (aka Rolondic f.) must be sandwiched between the pre-central and the post-central gyri. Those two gyri plus the central fissure run parallel to each other, as a unit, from the top of the cerebrum down to the lateral fissure (aka Sylvian f.), separating the temporal lobe from the frontal and parietal lobes. And if there aren't two such gyri, one in front one in back, then it ain't a central fissue.
The big deal about that for today's lesson, Doc, is that the primary motor cortex lies in the precentral gyrus. What are pre- to the blue marking here are frontal gyri, not the precental gyrus. (The frontal gyri run front to back -- at roughly right angles to the central fissure.) Anyway, we wanted you to see in the motor cortex just where the zone is for the eyelids (for blinking and winking). That's correctly shown in the photo.

COLLICULI
(back to Cranky's suggestions)

In this photo we can see three sets of colliculi in an oblique view of a sagittal section thru the brain stem, exposing the 4th ventricle and the cerebral aqueduct and presenting half a tectum (of the right side):

The cranial nerve nuclei for ocular motility conveniently lie at the same level as one pair of the colliculi:

SUPERIOR COLLICULUS -- Oculomotor (N III)
INFERIOR COLLICULUS -- Trochlear (N IV)
FACIAL COLLICULUS -- Abducens (N VI) (in floor of 4th ventricle)
The tectum (Latin for roof) -- collectively the superior and inferior colliculi (aka corpus [or lamina] quadrigenina) -- forms a sort of roof over the cerebral aqueduct (iter). A tegmentum exists in both the pons and the midbrain (mesencephalon) and represents part of the original embryonic brain stem. In the pons, it's what lies dorsal to the so-called 'pons propper' (i. e., the transverse fibers of the pons). In the midbrain, the tegmentum lies anterior to the cerebral aqueduct ; i. e., to the ventricular space of the midbrain. (Tegmentum means covering, in Latin.)
To appreciate this 'roof' and 'covering' business take a look at a cross section through the midbrain (click).
(back to Cranky's suggestions)

In this photo we can see three sets of colliculi in an oblique view of a sagittal section thru the brain stem, exposing the 4th ventricle and the cerebral aqueduct and presenting half a tectum (of the right side):
The cranial nerve nuclei for ocular motility conveniently lie at the same level as one pair of the colliculi: SUPERIOR COLLICULUS -- Oculomotor (N III) INFERIOR COLLICULUS -- Trochlear (N IV) FACIAL COLLICULUS -- Abducens (N VI) (in floor of 4th ventricle)	The tectum (Latin for roof) -- collectively the superior and inferior colliculi (aka corpus [or lamina] quadrigenina) -- forms a sort of roof over the cerebral aqueduct (iter). A tegmentum exists in both the pons and the midbrain (mesencephalon) and represents part of the original embryonic brain stem. In the pons, it's what lies dorsal to the so-called 'pons propper' (i. e., the transverse fibers of the pons). In the midbrain, the tegmentum lies anterior to the cerebral aqueduct ; i. e., to the ventricular space of the midbrain. (Tegmentum means covering, in Latin.) To appreciate this 'roof' and 'covering' business take a look at a cross section through the midbrain (click). (back to Cranky's suggestions)

(back to Cranky's suggestions)

SLIDE CONTROL PANEL (Slides 10, 16-21 are shown here.) For the entire set of neuroanatomy slides, go to (click): The Brain's Conscious Output .
Slide 09 Slide 10 Slide 16 Slide 17	Slide 18 Slide 19 Slide 20 Slide 21
(back to Cranky's suggestions)

Slide 09:
plane of sectioning:

Vestibular nuclei (4 in number) receiver the vestibular division of the auditory (acoustic) nerve (cranial nerve 8); these nuclei occupy occupy the latero-ventral aspect of the floor of the 4th ventricle throughout the extent of the space.
The MLF -- medial longitudunal fasciculus -- lies just ventral to the hypoglossal nucleus, (cranial nerve 12), whose cells innervate the muscles of the tongue. The hypoglossal nucleus lies on almost a direct line with the nuclei of the abducens, trochlear and occulomotor nerves.
(click for slide control)

Slide 10:

The dentate nucleus belongs to the cerebellum. plane of sectioning:
The facial colliculus is a bump in the floor of the 4th ventricle that provides a surface marker for fibers of the facial nerve (VII); those fibers swoop dorsally from the nucleus of VII and form a genu (or bend) around the abducens nucleus (VI); the arrow on the left points to fibers of the abducens nerve, en route to exit just below the pons (as seen in the last section). The fibers of VII, after making the bend around the abducens nucleus, leave this plane of sectioning, loop ventrally and exit at the inferior-lateral edge of the pons.
Note the location of the medial lemniscus.
click for slide control

Slide 16:

First, take note of the medial lemniscus. You can see the lateral lemniscus just above (dorsal) to it, here. (The lateral lemniscus is on its way into the inferior colliculus.) This section just nicked the lower ends of the two inferior colliculi (or auditory tectum). The MLF is still the medial longitudinal fasciculus. Note again the sup. (superior) cerebellar peduncle.
Note too the trochlear nerve (IVth cranial nerve); the big arrow points to trochlear fibers destined to exit just below the inferior colliculi. The latter fibers arose at a higher level (slide 18), then passed down (to the level in slide 15) where they crossed (or decussated). Do you see those two little dark dots at the end of the little arrow? Those dark dots are trochlear fibers in the anterior (superior) medullary velum descending toward their decussation; after decussating, they loop into the anterior medullary velum to execute their cross to the side opposite their origin. The big deal is that the trochlear nerve innervates a muscle, the superior oblique of the eye, on the contralateral side of the body.
plane of sectioning:

Note here the 4th ventricle. The latter space is directly in line with the cerebral aqueduct (iter). A ventricle, qua ventricle, must have some choroid plexus in it; that's also true of the lateral and third ventricles-- but not the cerebral aqueduct! (That's why the cerebral aqueduct is given a name but not a ventricle number. )
Note the mid. (middle) cerebellar peduncle. Also known as the brachium pontis, (can you guess why?), the middle cerebellar peduncle links the pons to the cerebellum. The superior cerebellar peduncle is also tagged in this section.
Again the pyramids (output pathways) can be seen passing vertically through the pons.
To return to the slide control panel, click here!

Slide 17:
plane of sectioning:

This a section of the midbrain (mesencephalon) at the level of the, inferior colliculi, and denotes the tectum or the tegmentum. (The inferior colliculi, are major reflex stations as well as major relays in the auditory (acoustic) pathways. When you jump from a sound, it's the inferior colliculi in action.) MLF is the medial longitudinal fasciculus.
To return to the slide control panel, click here!

Slide 18:

click for slide control
In a cross section through the midbrain (or mesencephalon) what lies above the cerebral aqueduct is the tectum (superior and inferior colliculi) and below, the midbrain tegmentum. Notice the MLF, medial longitudinal fasciculus and the medial lemniscus.
To return to the slide control panel, click here!

Slide 19:

click for slide control
The large upper arrow points to a superior colliculus. MLF is the medial longitudinal fasciculus; a recess of the interpeduncular fossa curls upwards at the upper border of the pons and here gives the false appearence of being a hole. Note especially the medial lemniscus and the heart-shaped oculomotor nuclear complex. The pineal body seemingly floats above the tectum; it's delicate stalk, is not in this plane (to appreciate why, click it).
The superior cerebellar peduncle carries the cerebellum's output to the thalamus and from there to the output part of the cerebral cortex (in the posterior part of the front lobe). The big deal about the massive decussation of the sup. cerebellar peduncles is that voluntary control of the body directly depends on the cerebral hemisphere on the opposite side.
To return to the slide control panel, click here!

Slide 20: -- PRETECTAL LEVEL: (back to Cranky's suggestions)

This section is just in front of the tectum (superior colliculi); thus the term "pre-tectal" area. LGB, lateral geniculate body (nucleus); P, pulvinar (of thalamus) on reader's left; Nuc. III, oculomotor (or 3rd cranial nerve) nuclear complex. The apparent difference in the two sides is because the section is slightly (but fortuitously) cockeyed in the horizontal plane.
Note on the left a small portion of the optic radiations (optic rads). The latter are fibers from cells in the LGB. Those fibers move up, into and contribute to the white matter of the cerebrum. The optic radiations (aka, the geniculo-calcarine tracts) fan out, some even extending forward into the temporal lobe (Meyer's loop), before turning back into occipital lobe and converging on the interior of the lips of the calcarine fissure;
{return to optic radiations 2}
Plane of sectioning:

centr. gray is a cylinder of central gray matter surrounding the cerebral aqueduct or iter (not labeled); post com., the posterior commissure is a bridge over the central gray matter used in pupillary reflexes; pre-text., the pretectal area(or nuclei), for which this plane of sectioning is named; br. sup. col., brachium (arm) of the superior colliculus, so-called because grossly that what it looks like -- an appendage of the superior colliculus; but it is a branch of the optic tract with input for internal eye reflexes. (On the left side the brachium appears as a dark triangle, apex skewed left, while on the reader's right the fibers of the brachium form a dark tuft squeezing between the pulvinar and the medial geniculate body (nucleus),m; sub. nigra, substantia nigra; F, interpeduncular fossa; U, uncus (contains the amygdala); the splenium of the corpus callosum lies at 12 o'clock.
To return to the slide control panel, click here!

Slide 21:
(back to Cranky's suggestions)

plane of sectioning:

CC, corpus callosum (body), LV, lateral ventricle; T, thalamus; 3, third ventrticle; IR, infundibular recess of third ventricle; m mammilliary body (nucleus); M-T, mammillo-thalamic tract. The arrow point just visible at 6 o'clock points to the infundibulum of hypothalamus.
Notice, among other things, how the uncus (of the temporal lobe) presses the optic tract against the Internal Capsule.
The Internal Capsule is just emerging onto the surface of the gross brain as the cerebral peduncle (basis... pes... crus cerebri). A lesion here (e.g., syphilitic gumma, glial tumor, hemorrhage) can simultaneously affect the opposite visual field (via the optic tract) and the voluntary control of muscles on the other side of the body.
To return to the slide control panel, click here!

(back to Cranky's suggestions)

CHECK LIST
(back to Cranky's suggestions)
A. CEREBRUM:

1) Occipital Lobe:

Occipital Pole:
Cuneate gyrus
Lingual gyrus
Calcarine fissure (sulcus)
Brodmann Map Areas: 17 (primary visual cortex); 18 and 19 (occipital eye fields)

2) Frontal Lobe:

Middle Frontal Gyrus -- posterior 1/5th (Brodmann area 8; Frontal Eye Fields)
Precentral gyrus (eyelid zone)

3) White Matter (Medullary Substance):

Optic Radiations
Splenium of the Corpus Callosum
Superior Longitudinal Fasciculus
Internal Capsule

B. DIENCEPHALON:	1. Optic Nerve (N II) 2. Optic Chiasm 3. Optic Tract	4. Brachium of the Superior Colliculus 5. Lateral Geniculate Body 6. Pulvinar (of the thalamus)	7. Pineal Body 8. 3rd Ventricle

C. PRETECTAL LEVEL:		1. Posterior Commissure	2. Pretectal Area (Nuclei)	3. Oculomotor Nuclei (N III)--rostral extreme

D. MIDBRAIN (mesencephalon):

1. Tectum (Corpora or Lamina Quadragemina): Superior Colliculi (Optic Tectum) Inferior Colliculi (Auditory Tectum)	2. Midbrain Tegmentum 3. Cerebral Aqueduct (Iter; Aqueduct of Sylvius)	4. Cerebral Peduncles (pes pedunculi) and Interpenduncular Fossa 5. Oculomotor Nerve (N III)	6. Oculomotor Nuclei 7. Superior (Anterior) Medullary Velum	8. Trochlear Nerve (N IV) 9. Medial Longitudinal Fasciculus (MLF) (slides 16-19).
E. PONS AND MEDULLA (Hindbrain):	1. Trigeminal Nerve (N V) 2. Medial Longitudinal Fasciculus (MLF) click to slides 16, 17, 18or19)	3. Facial (Facial-Abducens) Colliculus 4. Abducens Nucleus (Nucleus of N VI)	5. Abducens Nerve (N VI) 6. Vestibular Nuclei (collectively)
F. SPINAL CORD:	Cilio-Spinal Center (of Budge) [Lateral Gray Horn of cervical level 8 and thoracic levels 1 and 2]

Spinal cord -- gray horns
The Cilio-Spinal Center (of Burge) is in the lateral (intermediate) gray horn.

(back to Cranky's suggestions)

TRIGEMINAL AFFERENTS: Diagram of the sensory portions of Cranial Nerve V:

^*An item in the Electronic Reserve collection of the Indiana University School of Optometry Library

For the Neuroscience Audiotutorial menu at Shufflebrain click here!

For the second lesson in the visual system series (ANATOMY OF VISION II), click here.

{back to the top}

Slide 09:	plane of sectioning: Vestibular nuclei (4 in number) receiver the vestibular division of the auditory (acoustic) nerve (cranial nerve 8); these nuclei occupy occupy the latero-ventral aspect of the floor of the 4th ventricle throughout the extent of the space. The MLF -- medial longitudunal fasciculus -- lies just ventral to the hypoglossal nucleus, (cranial nerve 12), whose cells innervate the muscles of the tongue. The hypoglossal nucleus lies on almost a direct line with the nuclei of the abducens, trochlear and occulomotor nerves. (click for slide control)
Slide 10: The dentate nucleus belongs to the cerebellum.	plane of sectioning: The facial colliculus is a bump in the floor of the 4th ventricle that provides a surface marker for fibers of the facial nerve (VII); those fibers swoop dorsally from the nucleus of VII and form a genu (or bend) around the abducens nucleus (VI); the arrow on the left points to fibers of the abducens nerve, en route to exit just below the pons (as seen in the last section). The fibers of VII, after making the bend around the abducens nucleus, leave this plane of sectioning, loop ventrally and exit at the inferior-lateral edge of the pons. Note the location of the medial lemniscus. click for slide control
Slide 16: First, take note of the medial lemniscus. You can see the lateral lemniscus just above (dorsal) to it, here. (The lateral lemniscus is on its way into the inferior colliculus.) This section just nicked the lower ends of the two inferior colliculi (or auditory tectum). The MLF is still the medial longitudinal fasciculus. Note again the sup. (superior) cerebellar peduncle. Note too the trochlear nerve (IVth cranial nerve); the big arrow points to trochlear fibers destined to exit just below the inferior colliculi. The latter fibers arose at a higher level (slide 18), then passed down (to the level in slide 15) where they crossed (or decussated). Do you see those two little dark dots at the end of the little arrow? Those dark dots are trochlear fibers in the anterior (superior) medullary velum descending toward their decussation; after decussating, they loop into the anterior medullary velum to execute their cross to the side opposite their origin. The big deal is that the trochlear nerve innervates a muscle, the superior oblique of the eye, on the contralateral side of the body.	plane of sectioning: Note here the 4th ventricle. The latter space is directly in line with the cerebral aqueduct (iter). A ventricle, qua ventricle, must have some choroid plexus in it; that's also true of the lateral and third ventricles-- but not the cerebral aqueduct! (That's why the cerebral aqueduct is given a name but not a ventricle number. ) Note the mid. (middle) cerebellar peduncle. Also known as the brachium pontis, (can you guess why?), the middle cerebellar peduncle links the pons to the cerebellum. The superior cerebellar peduncle is also tagged in this section. Again the pyramids (output pathways) can be seen passing vertically through the pons. To return to the slide control panel, click here!
Slide 17:	plane of sectioning: This a section of the midbrain (mesencephalon) at the level of the, inferior colliculi, and denotes the tectum or the tegmentum. (The inferior colliculi, are major reflex stations as well as major relays in the auditory (acoustic) pathways. When you jump from a sound, it's the inferior colliculi in action.) MLF is the medial longitudinal fasciculus. To return to the slide control panel, click here!
Slide 18:	click for slide control In a cross section through the midbrain (or mesencephalon) what lies above the cerebral aqueduct is the tectum (superior and inferior colliculi) and below, the midbrain tegmentum. Notice the MLF, medial longitudinal fasciculus and the medial lemniscus. To return to the slide control panel, click here!
Slide 19: click for slide control The large upper arrow points to a superior colliculus. MLF is the medial longitudinal fasciculus; a recess of the interpeduncular fossa curls upwards at the upper border of the pons and here gives the false appearence of being a hole. Note especially the medial lemniscus and the heart-shaped oculomotor nuclear complex. The pineal body seemingly floats above the tectum; it's delicate stalk, is not in this plane (to appreciate why, click it).	The superior cerebellar peduncle carries the cerebellum's output to the thalamus and from there to the output part of the cerebral cortex (in the posterior part of the front lobe). The big deal about the massive decussation of the sup. cerebellar peduncles is that voluntary control of the body directly depends on the cerebral hemisphere on the opposite side. To return to the slide control panel, click here!
Slide 20: -- PRETECTAL LEVEL: (back to Cranky's suggestions) This section is just in front of the tectum (superior colliculi); thus the term "pre-tectal" area. LGB, lateral geniculate body (nucleus); P, pulvinar (of thalamus) on reader's left; Nuc. III, oculomotor (or 3rd cranial nerve) nuclear complex. The apparent difference in the two sides is because the section is slightly (but fortuitously) cockeyed in the horizontal plane. Note on the left a small portion of the optic radiations (optic rads). The latter are fibers from cells in the LGB. Those fibers move up, into and contribute to the white matter of the cerebrum. The optic radiations (aka, the geniculo-calcarine tracts) fan out, some even extending forward into the temporal lobe (Meyer's loop), before turning back into occipital lobe and converging on the interior of the lips of the calcarine fissure; {return to optic radiations 2}	Plane of sectioning: centr. gray is a cylinder of central gray matter surrounding the cerebral aqueduct or iter (not labeled); post com., the posterior commissure is a bridge over the central gray matter used in pupillary reflexes; pre-text., the pretectal area(or nuclei), for which this plane of sectioning is named; br. sup. col., brachium (arm) of the superior colliculus, so-called because grossly that what it looks like -- an appendage of the superior colliculus; but it is a branch of the optic tract with input for internal eye reflexes. (On the left side the brachium appears as a dark triangle, apex skewed left, while on the reader's right the fibers of the brachium form a dark tuft squeezing between the pulvinar and the medial geniculate body (nucleus),m; sub. nigra, substantia nigra; F, interpeduncular fossa; U, uncus (contains the amygdala); the splenium of the corpus callosum lies at 12 o'clock. To return to the slide control panel, click here!
Slide 21: (back to Cranky's suggestions)	plane of sectioning: CC, corpus callosum (body), LV, lateral ventricle; T, thalamus; 3, third ventrticle; IR, infundibular recess of third ventricle; m mammilliary body (nucleus); M-T, mammillo-thalamic tract. The arrow point just visible at 6 o'clock points to the infundibulum of hypothalamus. Notice, among other things, how the uncus (of the temporal lobe) presses the optic tract against the Internal Capsule. The Internal Capsule is just emerging onto the surface of the gross brain as the cerebral peduncle (basis... pes... crus cerebri). A lesion here (e.g., syphilitic gumma, glial tumor, hemorrhage) can simultaneously affect the opposite visual field (via the optic tract) and the voluntary control of muscles on the other side of the body. To return to the slide control panel, click here!

ANATOMY OF VISION I*

An Audiotutorial Overview of the Human Brain's VISUAL SYSTEM

SPECIAL SERIES ON THE OPTIC RADIATIONS

ANATOMY OF VISION I ^*

An Audiotutorial Overview of the Human Brain's
VISUAL SYSTEM