Eye muscle nerves and the ciliary ganglion of Malpolon monspessulana (Colubridae, Ophidia)

Abstract

In Malpolon monspessulana, the nervus oculomotorius arises from the ventral side of the pars peduncularis mesencephali of the midbrain by a single root. It runs closely applied to both the nervus abducens and the ramus nasalis of the nervus trigeminus. These nerves together with the nervus trochlearis leave the cranial cavity through the foramen orbitale magnum. Within this foramen the nervus oculomotorius divides into two rami: superior and inferior. The two rami innervate the rectus superior, rectus inferior, rectus medialis and the obliquus inferior muscles. The nervus trochlearis arises from the lateral side of the mesencephalon by a single root and passes to innervate the obliquus superior muscle. The nervus abducens arises from the ventral side of the medulla oblongata by a single root and passes for a distance through the vidian canal excavated in the parachordal cartilage. It innervates the rectus lateralis muscle. The eye muscle nerves carry special somatic motor fibres. The ciliary ganglion receives the preganglionic parasympathetic fibres from the ramus inferior of the nervus oculomotorius via the radix ciliaris brevis. Both the radix ciliaris longa and sympathetic root are absent. The ciliary ganglion is a well defined mass located in the postorbital region, irregular in shape formed of one type of neuron and gives off only one ciliary nerve.