The arachnoid and pia mater are essentially similar to the same structures on the spinal cord. The pia mater dips into the fissures and sulci of the brain.
II. THE PERIPHERAL NERVOUS SYSTEM.
1. Cranial Nerves. Nervi cerebrales.—
I. N. olfactorius.
—The fasciculi of the olfactory nerves arise from the olfactory bulb ([Fig. 144], a) and pass through the foramina of the cribriform plate, upon which the bulb lies, to be distributed to the olfactory mucous membrane of the nose.
II. N. opticus.
—The second nerve or optic ([Fig. 138], II) arises from the optic chiasma ([Fig. 138], c), passes through the optic foramen, and extends in an S-shaped curve to the eyeball. Its course is craniodorsad. It pierces the sclerotic and choroid coats of the eye and spreads out into the retina.
III. N. oculomotorius.
—The third or oculomotor nerve arises ([Fig. 138], III) from the pedunculus cerebri and passes into the orbit through the orbital fissure. It passes between the lateral and superior recti, sends a large branch to the superior rectus, supplies the medial rectus and the retractor oculi, passes laterad of the optic nerve and supplies the inferior rectus, and sends a long branch to the inferior oblique ([Fig. 166], f). At the point where the branch is given off to the inferior oblique muscle is the triangular reddish ciliary (or ophthalmic) ganglion, about two millimeters in diameter. It is directly attached to the inferior oblique branch of the third nerve and receives a delicate sensory filament from the ophthalmic nerve. From the ciliary ganglion proceed two short ciliary nerves which pass along each side of the optic nerve to the eyeball. These nerves penetrate the sclerotic at the sides of the eyeball to be distributed to the ball.