ANATOMICAL STUDIES ON THE CRANIAL NERVES OF THE SNAKE NATRIX TESSELLATA

Abstract

The present study deals with the cranial nerves of the colubrid Natrix tessellata.• The results can be summarized as follows : 1- The nervus terminalis arises from Jacobson's organ, in association with the vomeronasal nerve. It carries some ganglionic cells during its posterior course. 2- The nervi terminalis, vomeronasalis and olfactorius leave the nasal cavity through the foramen olfactorium advehens and enter the cranial cavity by penetrating the membranous cranial walL i.e., the forumen olfactorium evehens is missing. An olfactory peduncle is found between the olfactory bulb and the olfactory lobe. 3- The nervus opticus enters the orbital region through a special foramen in the fibrous sclera of the eye. 4- The nervi opticus, oculomotorius, trochlearis and abducens, as well as the ramus ophthalmicus profundus of the nervus trigeminus leave the cranial cavity through the foramen orbitale magnum. 5- The ramus inferior of the nervus oculomotorius gives off a radix ciliaris brevis which

tnmsmits the preganglionic parasympathetic fibres to the ciliary ganglion.

6- The cells of the ciliary ganglion are of two types. The ganglion is connected with ramus nasalis of the nervus trigeminus through the radix ciliaris longa. There is no direct sympathetic connection between the ganglion and :the internal carotid plexus. The ganglion gives off two ciliary nerves. 7- The nervus trochlearis has no connection with the other cranial nerves.

R- The nervus abducens passes a distance within the basisphenoiclbonc. It has no connection with the other cranial nerves. It innervates only the rectus lateral is muscle.