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NARVA

397

and backward across the posterior triangle of the neck to enter the trapeziums; both these muscles are in part supplied by the nerve. » The twelfth or hypoglussal nerve is motor, and rises from a nucleus in the floor of the fourth ventricle deep to the trigonum hypoglossi (see BRAIN, fig. 3). It emerges from the brain between the anterior pyramid and the olive (see fig. I), and leaves the skull in two bundles throu h the anterior condylar foramen. Soon after this it is closely bound' to the vagus, and, in front of the atlas, receives an important contribution from the loop between the first and second cervical nerves. The nerve then passes downward until it reaches the origin of the occipital artery, round which it loo s, and then runs forward on the surface of the hyo-glossus to the muscles of the tongue. As it bends round the occipital artery it gives off its descend ens hypoglossi branch, which derives its fibres from the communication with the first cervical already mentioned. This branch runs down and forms a loop with the communicants cervicis branch from the second and third cervical nerves, and from this loop (ansa hypoglossi) many of the depressor muscles of the hyoid bone and larynx are supplied. Farther forward special branches are given off to the thyro-h oid and genio-hyoid muscles, and these, like the descend ens hypogllossi, are derived from the first and second cervical loop, thus leaving all the true muscles of the tongue to be supplied by the medullary part of the nerve. For the embryology and comparative anatomy of the cranial nerves, see Nnnvous Svsrnn. II. SPINAL The spinal nerves are those which arise from each side of the spinal cord and are distributed to the trunk and limbs, though some of the upper ones supply the lower parts of the head and face. As is shown in the article NERvoUs SYSTEM, the division between cranial and spinal nerves is rather one of convenience than of any real scientific difference. There are generally thirty-one pairs of these nerves, which are subdivided according to the part of the vertebral column through which they pass out; thus there are eight cervical (abbreviated C.), twelve thoracic (Th.)-formerly called dorsal, -five lumbar (L), five sacral (S.) and one coccygeal (Coc.). As the thoracic nerves are the simplest and most generalized in their arrangement, a typical one of these, say the fourth or iifth, will be first described. The nerve is attached to the spinal cord by two roots, of which I r . in Fl J 1 V . ., 1 I 1' " ¢, , I Gu:.L.;- frlf ' ' Pl- ' r -=¢=====;: , <;.f-»~ Y°. -5 . » —- —if, WK - Jr, fe ° ' — ~— » we S -= '?r:"'Y"~2.» i, . ¢ =L 1- V. "" 'i: k E ¢ '~¢ g, ag 'j:; =. ¢  » .

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- Jqr 1lf 4 4:2 », 4 .34.1 Inn. @~, ,, :Q~.~, », lf. r f ~. - .¢' § .-.=.;, , » ¢r», , :' 5 K ... asus ., , .. i, n r

~ t qi;»< ¥lE 'l, l» x ' 4 ' J J1 r. .- . i, ar From A. M. Paterson, in Cunningham's TexI~Boalz nf Anatomy. FIG. 4.-The Distribution of the Pneumogastric Nerve. Va.R, Right vagi. I.C, Internal, and Va.L, Left vagi. E.C, External carotid arteries. 1, Ganglion of the root and Cal connexions with Sy, Sympathetic, vical ganglion. G.Ph, Glosso-pharyngeal. Acc, Spinal accessory nerve. superior cer- Ca2 C113 m, Menin 'cal branch. Auf, Auricuiar branch. Ca4 l, Ganglion of the trunk and connexions with Hy, Hypoglossal nerve. CI, C2 Loop 'between the first two cervical l'1C1'V@S. R.L, Superior cervical cardiac branch. lbranch. Inferior cervical cardiac Recurrent laryngeal nerve. Cardiac branches from recurrent laryngeal nerves. Thoracic cardiac branch (right vagus). A.P.Pl, Anterior, and P.P.Pl, Posterior pulmonary plexuses. 0es. Pl, Oesophageal plexus. Sy. Sympathetic. Gast. R, and Ga, sl. L, Gastric Acc, Spinal accessory nerve. T branches of vagus (right Ph, P aryngeal branch. and left). Ph.Pl, Pharyngeal plexus. Cae. Pl, Coeliac plexus. S.L, Superior laryngeal nerve. Hef. Pl, Hepatic plexus. I .L, Internal laryngeal branch. Sp .Pl, Splenic lexus. E.L, External laryngeal branch. Ren. Pl, Renal plexus. the ventral is purely efferent or motor and the dorsal purely afferent e or sensory. On t the foramen bedorsal root is a fusiform ganglion which lies in tween the verte- 'NTFFNM draw brae through 'Mm' ”""°" which the nerve passes. The two ' / roots then join to~, as c fasnw/an W /'0, '€/0] gether to form a l Q '°”/"MY mixed nerve (see ' iw, ” “Ms/6” Hg- 5), but very § $f§ Z'i soon divide once NIM more into anterior ' A (ventral) and pos- may t, ,, , t, ,, M terior (dorsal) 000' f;Z”5/, f fn/, ww primary divisions. QL, /' '/-V” These, however, '/ Caxfxfms each contain sensory and motor fibres. d]ust before V mmm it divi es in this B/*WC/ way the mixed nerve gives and receives its rami communicant es urnm with the sympa- """”" thetic (see NERvous SYsTEM). .wrre/on, ,, ,, ,, ,, ,, , The anterior r 7”//V* Wm primary division, runs 'round the trunk, between the, ,, ,, ,, ,, , K ribs, forming an emma/ ( intercostal nerve " and giving off a lateral cutaneous branch, when the side of the body is From A.M. Paterson, in Cunningham's T¢xt-Book of Anatomy. FIG. 5.-Scheme of the Distribution of a Typical Spinal Nerve. reached, which divides into anterior and posterior secondary branches. The rest of the division runs forward, supplying the intercostal muscles, as far as the edge of the sternum, when it ends in an anterior cutaneous branch to the front of the chest. The dorsal

primary division divides into an external (lateral) and internal

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