204 Neuroanatomy: Draw It to Know It
Extraocular Muscles: Oblique Muscles
Here, we will draw the oblique muscles. Once again,
establish the anterior–posterior, medial–lateral, and
superior–inferior axes. First, draw an axial view of the
superior oblique muscle in adduction. Show that the
superior oblique muscle runs across the superior surface
of the eyeball, hooks around the trochlea, which is Latin
for “pulley,” and runs along the medial wall of the orbit.
Next, show that in this position, the superior oblique
rotates the eye down. Th en, show that when the eye is
fully abducted, superior oblique force causes the eye to
intort. With the eye looking straight ahead, show that
the superior oblique causes intorsion, depression, and
also abduction.
For the inferior oblique, let’s use a coronal plane
because the inferior oblique attaches to the medial nasal
fl oor (unlike the other extraocular muscles, which attach
at the orbital apex at the annulus of Zinn). Draw the
inferior oblique fi rst in adduction. Show that in this
position, the inferior oblique causes elevation; then,
show that in abduction, it causes extortion; and lastly,
show that in primary position, it causes extorsion, eleva-
tion, and abduction.
Now, let’s use our fi st to demonstrate the rotational
pull of these eye muscles; we’ll start with the superior
oblique. Your right fi st is again the eyeball. Hook your
left thumb around your right index fi nger. Th e left thumb
is the trochlea and the right index fi nger is the superior
oblique. Pay attention to the spread between your index
and middle fi ngers. When the eye is fully adducted,
force along the trochlea depresses the eye; when the eye
is abducted, force along the trochlea intorts the eye; use
primary position to feel the superior oblique cause
eye abduction (although the superior oblique has multi-
ple actions in this position). For the inferior oblique, we
have to reverse our anterior–posterior plane: here, the
knuckles are posterior and the wrist is anterior; thus,
when the wrist is facing toward the body, it is in adduc-
tion, and when it is facing away from the body, it is in
abduction. With your wrist adducted, grip your right
index fi nger and pull; the eye elevates; then, in full
abduction, feel the inferior oblique cause the eye to
extort; use primary position to feel the inferior oblique
cause eye abduction (although the inferior oblique has
multiple actions in this position).^6 , 8 , 9