CHAP. IX.] XEEVOUS SYSTEM AXD OEGANS OF SENSE. 275 



oblongata, nearer the middle line than the origin of the ninth nerve. 

 Superficially it arises from the rcstiform body, close to and immedi- 

 ately below the ninth nerve, and springs from a considerable number 

 of roots — in a series one below another, forming a flat fasciculus. 

 It passes out of the jugular foramen beside the ninth nerve. It 

 developes two ganglia ; one near its root and one (Fig. 130, gpv) 

 on its trunk. 



It then descends the neck between the internal jugular vein and 

 carotid artery and passes into the thorax above the innominate vein 

 and root of the lung, whence it passes down the oesophagus, in the 

 posterior mediastinum, to the stomach. 



PJianjngccd and lanjncjeal hmnche>i go to the pharjTix and larynx 

 respectively. 



Cardiac hranches pass down to the heart, both from the cervical 

 and thoracic parts of the nerve. 



Pnlmonari/ branches arc given off to the lungs, the largest ones 

 being those which pass to those organs on the hinder aspect of the 

 lung root. 



The oesophagus also receives branches from the pneumogastric, 

 termed cesopltageal, on both sides of the lung root. 



The nerve ends in its gastric branches. The left pneumogastric 

 passes backwards on the ventral aspect of the oesophagus and is 

 distributed over the ventral side of the stomach (some fibres going 

 to the liver) while the right pneumogastric descends on the dorsal 

 aspect of the oesophagus and is distributed over the dorsal side of 

 the stomach — some fibres going to the spleen. 



The ELEVENTH, or SPINAL ACCESSORY norve (Figs. 128, XL, and 

 130, "), is a comparatively insignificant one. It takes origin lower 

 down than any other nerve reckoned as belonging to the encephalon, 

 namely, below the foramen magnum, from the side of the myelon, 

 by a series of delicate roots. Ascending into the skull through the 

 great occipital foramen, it passes out again through the jugular 

 foramen, in two divisions. One division is completely united with 

 the pneumogastric — the union commencing at the ganglion of the 

 root of that nerve and being completed below the ganglion of its 

 trunk. The other division turns backwards and supplies the stcrno- 

 mastoid and trapezius muscles. 



The TWELFTH, or HYPOGLOSSAL uorvo (Figs. 128, XIL, and 130, ^-), 

 is the nerve of the muscles of the larynx and hyoid, including the 

 tongue, to which it conveys motor impulses. Its deep origin is in the 

 grey matter of the posterior part of the medulla oblongata, close to 

 the posterior fissure. Its fibres are said to undergo a partial decussa- 

 tion in the floor of the fourth ventricle. It quits the encephalon by 

 scattered roots which come forth between the anterior pyramid and 

 the ohvary body in a line mth what we shall find to be the anterior 

 roots of the spinal nerves situated below. The roots collect and pass 

 through the anterior condyloid foramen. Thence the nerve descends 

 to the inferior margin of the digastric and then turns forwards and 



runs, above the hyoid, to the under part of the tongue. 



T 2 



