- There are twelve pairs of cranial nerves in animals-
- The first pair or olfactory nerve joins the convex ventral face of the olfactory bulbs.
- The second pair or optic nerve arises from the lateral geniculate bodies; the optic tracts converge to the optic chiasma and are then continued as optic nerves.
- The third pair or oculomotor nerve arises from the ventral face of the cerebral peduncle at the interpenduncular fossa.
- The fourth pair or trochlear nerve arises from the dorsal aspect behind the posterior colliculus of midbrain, pass outwards and emerge between the pons and the cerebral hemispheres.
- The fifth pair or trigeminal nerve is connected to the lateral part of the pons by a large sensory and a small motor root.
- The sixth pair or abducent nerve arises behind the pons lateral to the anterior ends of pyramids of the medulla.
- The seventh pair or facial nerve and the eighth or auditory nerve arise close together from the lateral part of corpus trapezoideum.
- The ninth pair or glossopharyngeal nerve
- Tenth and eleventh- vagus nerve and spinal accessory nerve arise in a series from the lateral aspect of the medulla behind the seventh. The spinal accessory nerve has two roots-a medullary and a spinal. A spinal root arises from the first five cervical segments of spinal cord and joins with the medullary root of spinal accessory nerve.
- The twelfth pair or hypoglossal nerve arises lateral to the posterior part of the pyramids of the medulla.
The brain is anatomically may be divided into cerebrum, cerebellum, pons, and medulla oblongata. For description five divisions may be considered. These are cerebral hemispheres, inter brain, mid brain, hind brain and medulla oblongata.
