Page:The New International Encyclopædia 1st ed. v. 14.djvu/438

* NEKVOUS SYSTEM AND BRAIN. 388 NERVOUS SYSTEM AND BRAIN. nerve cells of the sensory i)art are situatcii in two small ganglia, the jugular ganglion and the |)etrous ganglion. The eentral proees.ses of these cells enter the medulla and terminate in a nucleus in the lloor of the fourth ventricle, which is common to this nerve and the tenth. The cells whose axones make up the motor root are situ- ated in a nucleus which is called the nucleus ambiguus because of its connection with this nerve and the tenth, and which lies dee]) in the fornia- tio reticularis. The two parts of the nerve unite and leave the skull through the jugular foramen. Branches of this nerve are distributed to the traipanum, to the carotid, to the muscular coat and mucous membrane of the pharynx, to the stylo-pharyngeus, to the tonsil, and to the tongue. The tenth, vagus, or pneumogastrie nerve, leaves the medulla just behind the ninth. It is composed of two portions, a sensory and a motor, which arc connected with the already described nuclei common to both ninth and tenth nerves. The nerve leaves the cranial cavity through the jugular foramen. In the foramen it presents a swelling known as the ganglion jiigulare or ganglion of the root, while just outside the fora- men is a second ganglion, the inferior ganglion or ganglion of the trunk. It is in these two ganglia that the cell bodies of the sensory neu- rones of the nerve are situated. After its exit from the foramen, the nerve passes vertically down the neclc within the sheath of the carotid vessels. The eleventh nerve, or spinal accessory, is compo.sed of two parts, a spinal part and a cerebral part, or part accessory to the vagus. The latter is the smaller, an<l arises from a group of cells situated in the medulla below the nucleus of the vagus. It leaves the medulla as three or four small filaments just below the exit of the vagus. It passes through the jugular foramen in a sheath common to it and the vagus. The spinal portion of the nerve originates in a long nucleus situated in the lateral region and ex- tending from the middle of the medulla to the fifth or sixth cervical nerve. The fibres leave the cord in the mid-lateral region and pa.ss through the jugular foramen. The twelfth, or hypoglossal nerve, serves as the motor nerve for the tongue. Its nucleus is situated in the middle and lower part of the medulla, in the floor of the fourth ventricle, and ventral and lateral to the central canal. Fibres from this nucleus leave the medulla in bundles, from ten to fifteen in number, between the olive and the anterior pyramids. The nerve passes through the anterior condyloid foramen. The branches of distribution are the deseendens noni, the thyrohyoid muscular branches, and menin- geal branches. TirE Sympathetic Xervovs System. This is C(unposed of (a) two series of ganglia which are connected with one another by nerve fibres and extend along either side of the vertebral column from the base of the skull to the coccyx; (b) plexuses, three in number, which lie in front of the spine in the thoracic, abdominal, and pelvic caTities; fc) smaller ganglia which are situated in or upon various viscera: (d) nerve fibres which serve to connect the ganglia with one an- other, with the cercbro-spinal system, and with the periphery. The series of ganglia is known as the gangli- ated cord and may be subdivided into three cer- vical, twelve dorsal, four lumbar, and five sacral ganglia. In the neck these ganglia lie upon the transverse processes of the vertebra-, in the thora.x upon the heads of the ribs, in the abdo- men and pelvis, upon the bodies of the vertebroe and upon the sacrum. As the two cords pass into the pelvis they unite in a ganglion called the ganglion impar. in front of the coccyx. Superi- orly, the qangliated cord is continued into the sympathetic plexus on the carotid artery, this plexus lieing cimnected by filaments with the lower cranial nerves. The ganglia are connected ■Pfuvyn^tfraiis. Card-brans. -I?eep cardpUx. ■Supf^card-pia. -SoIarpUx. -Aor.plex, ■IfypoffpUx. Sac. gang. Gang.Unpar THE SYMPATHETIC NEBTE. Caro. plex., carotiil plexus; iSwp. cerv. gang., superior C(-'rvli'ul KiiUM^Hon ; Mid. ccrv. ganu., middle cervical praii- gli4.>n ; liij. cerv. yang., liiferi<)r cervical panpliim ; Dor$, ganfi., dorsal {^auKlia : Lu mb. gana.^Xwmhav Kuiigliii; Sac. fffirtff., sncrftl gaii^lin: Gano- if"l>ar. ffanplion impur; Pharifn. brans., phar.viifrcRl braucliea; Card, brant., cariliac branches; Deep card, iilrr.. deep cardiac plexus; Sup/, card, pies., superficial cordiac plexus: Solar plex., solar jjIcxus: Aor. plex., aortic plexus; Hypog. plex., hypognstric plexus. with one another by bundles composed of inter- mingled gray fibres and white fibres, the white fibres being derived from the sjiinal nerves. The branches which connect the sympathetic ganglia with the cercbro-spinal system are composed of both white fibres (modullated) and gray fibres (noninedullated) . The former arc derived from the cerebrospinal axis and pass to the sympa- thetic, the latter originate in the sympathetic system and end in the ccrcbros|)inal. The three great gangliatcd plexuses are known respectively as the cardiac, the solar or epigas- tric, and the hypogastric. They are composed of nerve fibres and ganglia, the former coming from the cerebrospinal nerves and from the gangliatcd cord. The cardiac plexus consists of a superficial portion which lies in the concavity beneath the arch of the aorta, and of a deep portion situated between the aorta and trachea. ■^1