The Special Senses
. Tey allow the eyes to follow a mov-
ing object, and provide external “guy-wires” that help maintain
the shape of the eyeball and hold it in the orbit.
originate from the
(or annular ring) at the back of the orbit and run
straight to their insertion on the eyeball. Teir locations and
the movements that they promote are clearly indicated by their
superior, inferior, lateral
medial rectus muscles
Te actions of the two
are less easy to deduce
because they take rather strange paths through the orbit. Tey
move the eye in the vertical plane when the eyeball is already
turned medially by the rectus muscles. Te
originates in common with the rectus muscles, runs
along the medial wall of the orbit, and then makes a right-angle
turn and passes through a ﬁbrocartilaginous loop called the
le-ah; “pulley”) suspended from the frontal bone
before inserting on the superolateral aspect of the eyeball. It
rotates the eye downward and somewhat laterally.
Superior oblique muscle
Superior oblique tendon
Superior rectus muscle
Lateral rectus muscle
(a) Lateral view of the right eye
(b) Superior view of the right eye
(c) Summary of muscle actions and innervating cranial nerves
Moves eye laterally
Moves eye medially
Elevates eye and turns it medially
Depresses eye and turns it medially
Elevates eye and turns it laterally
Depresses eye and turns it laterally
Controlling cranial nerve
Extrinsic eye muscles.
inferior oblique muscle
originates from the medial
orbit surface and runs laterally and obliquely to insert on the
inferolateral eye surface. It rotates the eye up and laterally.
Te four rectus muscles would seem to provide all the eye
movements we require—medial, lateral, superior, and inferior—
so why the two oblique muscles? Te simplest way to answer
this question is to point out that the superior and inferior recti
cannot elevate or depress the eye
without also turning it medially
because they approach the eye from a posteromedial direction.
For an eye to be
elevated or depressed, the lateral pull of
the oblique muscles is necessary to cancel the medial pull of the
superior and inferior recti.
Except for the lateral rectus and superior oblique muscles,
which are innervated respectively by the
serve all extrinsic eye muscles.
Figure 15.3c summarizes the actions and nerve supply of these
muscles. ±able 13.2 (pp. 495–497) illustrates the courses of the
associated cranial nerves.