The glossopharyngecal nerve is principally au afferent or sensory nerve, but has a small motor root. It escapes from the cranium in association with the pueumogastric and spina: accessory nerves, through the same foramen as that through which the jugular vein emerges. It then descends by the side of the pharynx, and after anastomising with the facial and pneumogastric nerves, and giving off a branch to the tympanum of the ear, terminates in branches to the mucous membrane of the base of the tongue, of the palate, tonsils, and pharynx, and in twigs to the digastrie and muscles; so that its distribution is almost entirely to sentient surfaces. From a careful examina tion of the investigations of Dr. John tteid and others regarding the functions of this nerve, Todd and Bowman arrive at the following conclusions: 1. "It is the sensitive nerve of the mucous membrane of the fames and of the root of the tongue, and in the latter situation it ministers to 'taste and touch, as well to common sensibility; and being the sensitive nerve of the lances, it is probably concerned in the feeling of nausea, which. may be so readily excited by stimulating the mucous membrane of this region." 2. " Such are its peripheral organization and central connections, that stimulation of any part of the mucous membrane in which it ramifies, excites instantly to contraction all the facial muscles supplied by the pneumogastric and the facial nerves; and the permanent irrita tion of its peripheral ramifications, as in the case of sore throat. will effect other muscles supplied by the facial nerve likewise. It is, therefore, an excitor of the movements necessary to pharyngeal deglutition."—Op. cit. vol. ii., p.119.
The pneumo,qastrte nerve, or par vagum, is distributed to so many important organ. (the larynx. heart, lungs, stomach, etc.), and is of such great physiological importance, that a special article is devoted to its consideration.
The spinal accessory nerve is more remarkable for its peculiar course than in any other respect. It rises from the spinal cord at the level of the fifth or sixth cervical nerve, passes upwards between the anterior and posterior roots of the cervical nerves into the skull, and =cages from the.Cianial cavity with timtwo preeedingaterves. It is chiefly distributed to the irnpezins Muscle.
In the above remarks on the cranial nerves, we have omitted all notice of their points of °Haim as that subject is sufficiently noticed in the article Ilium We shall now briefly notice the mode in which the extremities receive their nerves. These nerves are derived from 111e spinal nerves, through the intervention of what is termed in anatomy a plexus. Four or five nerves proceed from the spinal cord for a certain distance, without any communication with each other. They then divide, and from the conjunction of the adjacent branches new nerves result, which again subdivide and interchange fibers. From the net-work or plexus thus formed nerves emerge, each of which is composed of fibers derived from several of the original branches. The most
important of these plexuses are found in the regions of the neck, the axilla, the loins, and the sacrum, and are known as the cervical, brachial, lumbar, and sacral plexuses.
The brachial plexus is formed by communication between the anterior roots of the last four cervical nerves and the first dorsal nerve. These nerves are nearly equal in size, and their mode of distribution is sufficiently explained by the diagram. The branches emerging from this plexus supply the shoulder and the arm; and the names of the most imporant of these branches arc given in the description attached to clic figure.
The brnthar and sacral plexuses, with the nerves of the lower extremity, are shown in Fig. 2. The description attached to the diagram sufficiently explains the mode of forma tion and the distribution of the branches of these plexuses.
The general arrangement of the sympathetic system, or. as it is sometimes termed, the sympathetic nerve, has been already noticed at the beginning of this article. Its cephalic portion consists of four ganglia on either side—viz., (1) the ophthalmic. or lenticular gan glion; (2) the spheno-palatine, or Meckel's ganglion; (3) the otic, or Arnold's ganglion; and (4) the submaxillary ganglion. They are all closely connected with the branches of the trifacial nerve. The cervical portion contains 3 ganglia, the dorsal 12, the lumbar 4, the sacral 5, and the cocygeal 1, which, instezd of lying on the side of the vertebral column, is placed in front of the coccyx, and forms a point of convergence for the two ganglionated cords which run from the cervical to the sacral region parallel to one another. Then ganglion may be regarded as a distinct nervous center, from which branches pass oil in various directions. In addition to the cords of communication between the ganglia, certain seta of nerves mayli:q 'really traced—viz., (1) visceral nerves, which generally accompany branches of arteries to the viscera (the lungs, heart, kidneys, liver, spleen. and intestines, etc.); (2) arterial branches, distributed to arteries in the vicinity of the ganglia; and (3) branches of communication with the cerebral and spinal nerves.
The only sympathetic nerve that our limited space will permit us to notice is the great splanchnie. This nerve arises by separate roots from the 5111, Pith, 7th, 8th, and 9th thoracic ganglia. These roots unite to form a large round cord, which passes obliquely downwards and forwards, and after entering the abdomen by piercing the diaphragm, ends in a large and complex ganglion, the semilunur ganglion, which lies upon the side and front of the aorta, at the origin of the coeliac axis. The semilunar ganglia, with Vie nerves entering and emeqing front them, combine to form the solar plcius, which, from the mass of nervous matter which it contains, has been termed the abdominal brain. It is ill consequence of the existence of this great nervous center, that a blow in the region in which it lies always inflicts 4 severe nervous shock, and not unfrequently causes death.