The =trochlear= or pathetic (N. trochlearis) is the smallest of the
cranial nerves. It arises from the anterior cerebellar peduncle just
behind the corpora quadrigemina, curves outward and forward, pierces the
tentorium cerebelli, and passes forward along the outer border of the
maxillary nerve (Figs. 504, 505). It emerges from the cranium through a
small foramen immediately above the foramen lacerum orbitale or through
the latter and passes forward along the inner wall of the orbit to end
in the posterior part of the superior oblique muscle of the eyeball
(Fig. 439).
The fibers of the fourth nerve spring from a nucleus in the gray
matter of the floor of the cerebral aqueduct behind the oculomotor
nucleus. The fibers run backward in the tegmentum, then turn upward
and inward and undergo total decussation with those of the opposite
nerve in the anterior part of the anterior medullary velum. In
addition to this peculiarity it is the only nerve which is connected
with the dorsal aspect of the brain.