A Treatise on Anatomy, Physiology, and Hygiene Part 49

750. The FACIAL NERVE (eighth pair) pa.s.ses from the skull through an opening situated below the ear, (_mastoid foramen_.) It is distributed over the face, supplying the muscles with nervous filaments.

748. What is said of the abducentes, or sixth pair of nerves? 749. Of the portio mollis? Explain fig. 127. 750. Of the facial nerve?

751. The GLOSSO-PHARYNGEAL NERVE (ninth pair) pa.s.ses from the brain, through an opening with the jugular vein, (_foramen lace-rum_.) It is distributed to the mucous membrane of the tongue and throat, and also to the mucous glands of the mouth.

752. the PNEUMOGASTRIC NERVE (tenth pair) escapes from the brain through the foramen lacerum. It sends branches to the larynx, pharynx, oesophagus, lungs, spleen, pancreas, liver, stomach, and intestines.

(Fig. 132.)

753. The SPINAL ACCESSORY NERVE (eleventh pair) has its origin in the respiratory tract of the spinal cord. It connects with the ninth and tenth pairs of nerves, and is distributed to the muscles about the neck.

754. The HYPO-GLOSSAL NERVE (twelfth pair) pa.s.ses from the brain, through a small opening, (_condy-loid foramen_.) It ramifies upon the muscles of the tongue, and is its motor nerve.

_Observation._ The cranial nerves, with the exception of the olfactory, optic, and auditory, connect with each other by means of filaments. They also send connecting nervous filaments to the upper spinal nerves, (cervical,) and the sympathetic nerve.

751. Describe the glosso-pharyngeal nerve. 752. The pneumogastric nerve. 753. The spinal accessory nerve. 754. The hypo-glossal nerve.

CHAPTER x.x.xVII.

ANATOMY OF THE NERVOUS SYSTEM, CONTINUED.

755. The spinal column contains the spinal cord, the roots of the spinal nerves, and the membranes of the cord.

756. The SPINAL CORD extends from the medulla oblongata to the second lumbar vertebra, where it terminates in a rounded point. It presents a difference of diameter in different parts of its extent, and exhibits three enlargements. The uppermost of these is the medulla oblongata.

There is no distinct demarkation between this enlargement and the spinal cord. The next corresponds with the origin of the nerves distributed to the upper extremities; the third enlargement is situated near the termination of the cord, and corresponds with the attachment of the nerves which are intended for the supply of the lower extremities.

757. An anterior and posterior fissure divides the spinal cord into two lateral cords. These are united by a thin layer of white substance. The lateral cords are each divided by furrows into three distinct sets of fibres, or columns; namely the _anterior_, _lateral_, and _posterior_ columns. The anterior are the motor columns; the posterior are the columns of sensation; the lateral columns are divided in their function between motion and sensation. They contain the fasciculus described, by Sir Charles Bell, as the respiratory tract.

[Ill.u.s.tration: Fig. 128. A section of the brain and spinal column. 1, The cerebrum. 2, The cerebellum. 3, The medulla oblongata. 4, 4, The spinal cord in its ca.n.a.l.]

[Ill.u.s.tration: Fig. 129. Anterior view of the brain and spinal cord. 1, 1, The two hemispheres of the cerebrum. 3, 3, The cerebellum. 4, The olfactory nerve. 5, The optic nerve. 7, The third pair of nerves. 8, The pons varolii. 9, The fourth pair of nerves. 10, The lower portion of the medulla oblongata. 11, 11, The spinal cord. 12, 12, Spinal nerves. 13, 13, The brachial plexus. 14, 14, The lumbar and sacral plexus.]

755-767. _Give the anatomy of the spinal cord, spinal nerves, and the sympathetic nerve._ 755. What does the spinal column contain? 756.

Give the extent of the spinal cord. How many enlargements has this cord? What is said of each enlargement? 757. Into how many parts is the spinal cord divided? Give the function of these columns.

758. The SPINAL NERVES, that connect with the spinal cord, are arranged in thirty-one pairs, each arising by two roots; an anterior, or _motor_ root, and a posterior, or _sensitive_ root. Each nerve, when minutely examined, is found to consist of an aggregate of very delicate filaments, enclosed in a common cellular envelope.

758. How many pairs of nerves issue from the spinal cord? Explain fig.

128. Fig. 129.

759. The anterior roots arise from a narrow white line upon the anterior columns of the spinal cord. The posterior roots arise from a narrow gray band formed by the internal gray substance of the cord.

They are larger, and the filaments of origin more numerous than those of the anterior roots. A ganglion is found upon each of the posterior roots in the openings between the bones of the spinal column through which the nerve pa.s.ses.

[Ill.u.s.tration: Fig. 130. A section of the spinal cord, surrounded by its sheath. B, A spinal nerve, formed by the union of the motor root (C) and the sensitive root (D.) At D, the ganglion upon this root is seen.]

760. After the formation of the ganglion, the two roots unite, and const.i.tute a spinal nerve, which pa.s.ses through the opening between the vertebr on the sides of the spinal column. The nerves divide and subdivide, until their minute filaments ramify on the tissues of the different organs.

759. Give the origin of the anterior roots. Of the posterior roots. In what respect do the posterior roots differ from the anterior? 760.

When do the two roots unite, and where do they pa.s.s?

761. The _spinal nerves_ are divided into--

Cervical, 8 pairs, Dorsal, 12 "

Lumbar, 5 "

Sacral, 6 "

762. The four lower cervical and upper dorsal pa.s.s into each other and then separate to reunite. This is called the _brachi-al plexus_.

From this plexus six nerves proceed, which ramify upon the muscles and skin of the upper extremities.

763. The last dorsal and the five lumbar nerves form a plexus called the lumbar, similar to that of the cervical. Six nerves pa.s.s from this plexus, which ramify upon the muscles and skin of the lower extremities.

764. The last lumbar and the four upper sacral unite to form the sacral plexus. From this plexus five nerves proceed, that are distributed to the muscles and skin of the hip and lower extremities.

765. The SYMPATHETIC NERVE[19] consists of a series of _Gangli-a_, or knots, extending each side of the spinal column, forming a chain its whole length. It communicates with both the cranial and spinal nerves.

With the exception of the neck, there is a ganglion for each intervertebral s.p.a.ce. These ganglia are composed of a mixture of cineritious and medullary matter, and are supposed to be productive of peculiar nervous power.

[19] The structure of this nerve is very complicated, and different physiologists ascribe to it various functions. The character of its diseases are not well understood.

761. Give the division of the spinal nerves. 762. What nerves const.i.tute the brachial plexus? How many nerves pa.s.s from this plexus?

763. How many nerves from the lumbar plexus, and where do they ramify?

764. How is the sacral plexus formed? 765. Of what does the sympathetic nerve consist? How is the sympathetic nerve distributed?

What exception? Of what are the ganglia composed?