Part 48 (2/2)

5th. The _Tri-facial_. 6th. The _Ab-du-centes_. 7th. The _Porti-o Dura_. 8th. The _Porti-o Mollis_. 9th. The _Glosso-pha-ryngi-al_.

10th. The _Pneu-mo-gastric_. 11th. The _Spinal Acces-so-ry_. 12th.

The _Hypo-glossal_.

742. The OLFACTORY NERVE (first pair) pa.s.ses from the cavity of the skull through many small openings in a plate of the _ethmoid_ bone.

(This plate is called _cribri-form_, from its resemblance to a sieve.) This nerve ramifies upon the membrane that lines the nasal pa.s.sages. It is the softest nerve of the body. (Fig. 136.)

743. The OPTIC NERVE (second pair) pa.s.ses from the interior of the cranium, through an opening in the base of the skull, (_fo-ramen opti-c.u.m_,) to the cavity for the eye. It pierces the coats of the eye, and expands in the retina.

744. The MOTORES OCULORUM (third pair) pa.s.s from the brain, through an opening of the _sphenoid_ bone, (_sphe-noidal fissure_,) to the muscles of the eye.

739. Describe the arachnoid membrane. 740. What is said respecting the pia mater? 741. How many pairs of cranial nerves? Name them. 742.

Describe the olfactory nerve. 743. The optic nerve. 744. Describe the motores oculorum.

745. The PATHETICUS (fourth pair) pa.s.ses from the brain, through the sphenoidal fissure, to the superior oblique muscle of the eye.

[Ill.u.s.tration: Fig. 125. The distribution of the third, fourth, and sixth pairs of nerves, to the muscles of the eye. 1, The ball of the eye and rectus externus muscle. 2, The upper jaw. 3, The third pair, distributed to all the muscles of the eye, except the superior oblique, and external rectus. 4, The fourth pair pa.s.ses to the superior oblique muscle. 6, The sixth pair, is distributed to the external rectus muscle.]

746. The TRIFACIAL NERVE (fifth pair) is a.n.a.logous to the spinal nerves in its origin by two roots, from the anterior and posterior columns of the spinal cord. It has a ganglion, like the spinal nerves upon its posterior root. For these reasons, it ranges with the spinal nerves, and is considered the cranial spinal nerve. This nerve divides into three branches:--The _oph-thalmic_, superior _maxil-la-ry_, and inferior _maxil-la-ry_.

745. The patheticus. What does fig. 125 represent? 746. What is the trifacial nerve sometimes called? Why is it cla.s.sed with the cranial spinal nerves? Give the names of its branches.

747. The ophthalmic nerve pa.s.ses from the cranial cavity through the sphenoidal fissure. It sends branches to the forehead, eye, and nose.

The superior maxillary nerve pa.s.ses through an opening in the base of the skull, (_foramen ro-tunddum_,) and sends branches to the eye, the teeth of the upper jaw, and the muscles of the face. The inferior maxillary nerve escapes from the cranial cavity through an opening called _foramen o-vale_. It sends branches to the muscles of the lower jaw, the ear, the tongue, and the teeth of the lower jaw.

[Ill.u.s.tration: Fig. 126. The distribution of the fifth pair of nerves. 1, The orbit for the eye. 2, The upper jaw. 3, The tongue. 4, The lower jaw.

5, The fifth pair of nerves. 6, The first branch of this nerve, that pa.s.ses to the eye. 9, 10, 11, 12, 13, 14, Divisions of this branch. 7, The second branch of the fifth pair of nerves is distributed to the teeth of the upper jaw. 15, 16, 17, 18, 19, 20, Divisions of this branch. 8, The third branch of the fifth pair, that pa.s.ses to the tongue and teeth of the lower jaw. 23. The division of this branch that pa.s.ses to the tongue, called the _gusta-to-ry_. 24. The division that is distributed to the teeth of the lower jaw.]

747. Where do the filaments of the ophthalmic branch ramify? The superior maxillary? The inferior maxillary? Explain fig. 126.

748. The ABDUCENTES (sixth pair) pa.s.ses through the opening by which the carotid artery enters the cranial cavity. It is the smallest of the cerebral nerves, and is appropriated to the external straight muscle of the eye.

749. The PORTIO MOLLIS (seventh pair) enters the hard portion of the _tempo-ral_ bone at the internal auditory opening, and is distributed upon the internal ear. (Fig. 147, 148.)

[Ill.u.s.tration: Fig. 127. A representation of the distribution of the eighth pair of nerves with some branches of the fifth. 1, 2, 3, 5, 7, 9, Are branches of the eighth pair. They are distributed over the face in a radiated manner, which const.i.tutes the pes anserinus, (foot of a goose.) The nerves 4, 6, 8, are branches of the fifth pair. 10, 11, 12, 13, 14, 15, 16, Are branches of nerves from the upper part of the spinal cord, (cervical.)]

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