The Trochlear Nerve (IV)

The trochlear nerve, which is small, provides somatic efferent innervation to the dorsal oblique muscle. The nucleus of origin within the tegmentum of the midbrain gives rise to a fiber bundle that decussates internally before emerging from the rostral medullary velum (Fig. 8.22/8). The nerve then follows the edge of the tentorium cerebelli to the floor of the cranial cavity. In some species it makes a separate entrance to the orbit, but usually it passes through the orbital fissure. The effects of isolated damage to the trochlear nerve, rare as for others, are those of paralysis of the dorsal oblique muscle (p. 327).