The second branch communicates with the second and third cervical nerves, before it pierces the sterno mastoid muscle, and its filaments undoubtedly furnish motor power to that muscle and also to the trapezius. It is proven by ex

FIG. 146. A diagram of the spinal accessory nerve.

1, the accessory portion of the nerve arising from the medulla oblongata; 2, the spinal portion of the nerve arising from the spinal cord (cervical region); 3, a filament arising from the first and second cervical nerves and joining the spinal portion of the spinal accessory nerve, before passing through the foramen magnum; 4, the foramen magnum, showing the spinal portion of the nerve entering the cranium; 5, the jugular foramen, showing the spinal and accessory portions of the nerve communicating as they pass through it; 6, the large filament going to the pneumogastric to supply the muscles of the larynx, and the small filament returning to the trunk of the spinal accessory nerve; 7, 8, 9, filaments of communication between the spinal accessory nerve and the third, fourth, and fifth cervical nerves; 10, muscular branches to the sternocleidomastoid muscle; 11, muscular branches to the trapezius muscle; 12, communicating filaments from the cervical plexus of nerves.

periment, however, that section of the spinal accessory nerve does not produce total paralysis of these muscles; and, from

tions of Bernard and Bischoff have demonstrated the existence of other motor fibers to the larynx, irrespective of those of the spinal accessory, which seem to control the automatic respiratory movements of the glottis.

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this fact, it is conclusively proved that some other sources of nerve supply to these muscles exist, besides the spinal accessory filaments.

A TABLE OF THE BRANCHES OF THE SPINAL ACCESSORY NERVE.'

FUNCTIONS OF THE SPINAL ACCESSORY NERVE AND THE EFFECTS OF

SECTION.

The experiments of Bernard, to whose ingenuity much of our present knowledge of the function of the bulbar and spinal portions of this nerve is due, seem to warrant the conclusion that the bulbar or medullary part of the nerve possesses a direct control upon the muscles of the pharynx and larynx, but no effect whatever upon the sternomastoid and trapezius muscles. Galvanism of the spinal portion of the nerve seems to have a directly opposite effect, since the muscles of the pharynx and larynx were unaffected, and the two muscles of the neck to which the nerve is distributed were thrown into movement. It also appears from the results of this great experimenter that the nerve is essentially motor in its function at its origin from the medulla and spinal cord, but that it gains sensory fibers after it leaves the cavity of the cranium, by means

1

FIG. 147.-Glottis seen with the laryngoscope during the emis sion of high-pitched sounds. (Le Bon.)

1, 2, base of the tongue; 3, 4, epiglottis; 5, 6, pharynx; 7, arytenoid cartilages; 8, opening between the true vocal cords; 9, aryteno-epiglottidean folds; 10, cartilage of Santorini: 11, cuneiform cartilage; 12, superior vocal cords; 13, inferior vocal cords.

Modified from a table in the "Essentials of Anatomy" (Darling and Ranney). Putnam's Sons, New York, 1880.

of certain filaments of communication derived from the cervical nerves and the pneumogastric. This fact probably explains why two points of communication should exist between the spinal accessory and the pneumogastric nerves; since, at one point, the sensory filaments of the pneumogastric were given to the spinal accessory, while, at the other point, the motor filaments of the spinal accessory were sent to the pneumogastric sheath for protection, until they could be distributed to the muscles of the larynx.

Bernard and Bischoff have probably done more to clear up the disputed relation of the spinal accessory nerve to the muscles of the larynx, and thus to the acts of phonation and respiration,' than any of the later investigators upon the physiology of the nervous system. When the spinal accessory nerve is drawn out from the medulla and spinal cord of an animal, as can be done with little if any injury to the nerve, if the requisite care and skill be employed, the effect is at once manifested in the voice, which becomes hoarse and unnatural, when the nerve of one side only is extracted, but entirely extinct when both nerves are thus treated. The act of deglutition is also somewhat affected, and the trapezius and sternomastoid muscles are paralyzed, but only to a partial extent.

An interesting relation of the spinal accessory nerve to the action of the heart seems to be well shown by the experiments of Waller, who first called the attention of the profession to the fact that extirpation of the roots of the spinal accessory nerve produced a modification in the effects of galvanism of the trunk of the pneumogastric nerve, provided that sufficient time (some two weeks) was allowed after the operation for the irritation so produced to subside. As has been mentioned in the previous lecture upon the pneumogastric nerve,' galvanism of that nerve with a powerful current will arrest the action of the heart in a state of health, even if

The nerves concerned in the two acts of phonation and respiration are not to be confounded, since it is probable that the pneumogastric nerve sends filaments of a motor character to the larynx, which are independent of the spinal accessory nerve, and which probably preside over the respiratory movements of the glottis, while the spinal accessory nerve controls phonation. 2 See page 482 of this volume.

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applied on one side of the body. Now, Waller found that after the spinal accessory nerve of one side had been drawn out, and the animal allowed to recover the shock of the operation, and to wait some days for all signs of irritation to subside, galvanism of the pneumogastric nerve of the same side no longer seemed to affect the action of the heart. The de

1, large root of the fifth nerve; 2, ganglion of Gasser; 3, ophthalmic division of the fifth; 4, superior maxillary division; 5, inferior maxillary division; 6, 10, lingual branch of the fifth, containing the filaments of the chorda tympani; 7, branch from the sublingual to the lingual branch of the fifth; 8, chorda tympani; 9, inferior dental nerve; 10, terminal branches of the gustatory nerve; 11, submaxillary ganglion; 12, mylo-hyoid branch of the inferior dental nerve; 13, anterior belly of the digastric muscle; 14, section of the mylo-hyoid muscle; 15, 18, glosso-pharyngeal nerve; 16, ganglion of Andersch; 17, branches from the glosso-pharyngeal to the stylo-glossus and the stylo-pharyngeus muscles; 19, 19, pneumogastric; 20, 21, ganglia of the pneumogastric; 22, 22, superior laryngeal nerve; 23, spinal accessory; 24, 25, 26, 27, 28, sublingual nerve and branches.

pressor nerve of the heart, which arises from both the superior laryngeal and pneumogastric nerves, since it has two heads, must, therefore, be in some way connected with the

spinal accessory nerve. It may, therefore, be stated with as much positiveness as any physiological point can be laid down, that the communicating filament given off by the spinal accessory nerve to the pneumogastric controls the muscles of phonation.

The distribution of the spinal accessory nerve to only two of the muscles of the neck-the sterno-mastoid and the trapezius-would naturally suggest, to the inquiring mind, why these muscles should have been singled out as particularly associated with this nerve. Throughout this entire course of lectures I have frequently called your attention to the fact, which can not be too often repeated, that the distribution of nerves to muscles always denotes a purpose on the part of Nature, and a similarity of function in the muscles supplied by the same nerve, if we will but search for it. Now, we have already seen that the spinal accessory nerve is chiefly destined to control the muscles of phonation, since other nerve fibers go to the larynx, which assist in moving the vocal cords during the opening of the glottis, previous to each inspiratory act; therefore, the spinal accessory nerve can not be said to be directly concerned with the respiratory func tion. If we will study the attitude assumed by a vocalist in the act of singing (and it is in the singing act, rather than that of talking, that we see the mechanism of phonation best displayed, since it requires more of a muscular effort than the simple articulation of words), we shall perceive that the sterno-mastoid and the trapezius muscles are important factors in the production of voice, as they tend to fix the shoulders (that is, the scapulæ and the clavicles) and also the upper part of the sternum. In all vocal efforts, the first act necessary to its performance is a full inspiratory effort, which can only be performed by first calling into play those muscles which render the upper portion of the chest and the bones of the shoulder immovable, so as to have a fixed point from which the true inspiratory muscles can act upon the ribs and their cartilages; and it can, therefore, be understood why these muscles should properly be placed under the control of