SPINAL x\CCESSORY AXD HYPOGLOSSAL NERVES. 565 



cells giving origin to the pneumogastrie nerve. The lower or spinal 

 roots pass through the lateral column of the cord, and enter the grey 

 substance midway between the anterior and posterior coraua. They 

 then curve forwards into the anterior horn, and are believed to be 

 connected with its large nerve-cells, especially with the outer group. 



Course and distribution. — The infernal or accessor// jxai, the 

 smaller of the two, joins in the foramen of exit the ganglion on the 

 root of the pneumogastrie, by two or three filaments ; and having 

 passed from the skull, blends Avith the trunk of the pneumogastrie 

 beyond its second ganglion, as already said. 



It is stated by Bendz that a filament is given from the spinal accessory to the 

 pharj-ngeal nerve above the jilace of junction with the pneumogastrie. and the 

 fibrils of the same nerve have been traced into each of the muscular offsets of the 

 pneumogastrie nerve. (Bendz, " Tract, de connexu inter nerv. vag. et acces." 1836.) 



The external portion of the nerve communicates with the accessory 

 part in the foramen jugulare. After issuing from the foramen, the 

 nerve is dn-ected backwards in front of the internal jugular vein, and 

 perforates the stcrno-mastoid muscle, supplying this with branches, and 

 joining amongst the fleshy fibres with blanches of the cervical plexus. 

 Descending in the next place across the neck behind the sterno-mastoid, 

 the nerve ]msses beneath the trapezius muscle. Here it forms a kind of 

 plexus with branches of the third and fourth cervical nerves, and dis- 

 tributes filaments to the trapezius, which extend nearly to the lower 

 edge of the muscle. 



Varieties. — The spinal accessory nerve frequently passes behind the internal 

 jugular vein. It has also been found to pass behind the stenio-mastoid muscle 

 without piercing it (Turner, Nat. Hist. Review, 1SG4). 



NINTH PAIR OF NERVES. 



The hypoglossal or ninth cranial nerve is the motor nerve of the 

 tongue, and in part of some of the muscles of the neck. 



Surface attachment. — The nerve arises, by a series of fine roots, 

 from the furrow between the anterior pyramid of the medulla and the 

 olivary body. 



Deep origin. — The bundles of fibres pass backwards, through the 

 inner part of the olivary body, to reach their nucleus, a column of 

 large branching nerve-cells lying in front of and close to the central 

 canal, as low as the decussation of the pyramids. Above, where the 

 canal opens into the floor of the fourth ventricle, the nucleus comes to 

 the surface, causing a prominence close to the middle line, a little 

 above the point of the calamus scriptorius. 



Course and distribution. — The filaments by which this nerve arises 

 from the medulla oblongata are collected into two bundles, which con- 

 verge to the anterior condylar foramen of the occipital bone. Each 

 bundle of filaments perforates the dura mater separately within the 

 foramen, and the two are joined after they have passed through it. 



After leaving the cranium, this nerve descends almost vertically to 

 the lower border of the digastric muscle, where, changing its course, it 

 is directed forwards above the hyoid bone to the under part of the 

 tongue. It lies at first very deeply with the vagus nerve, to which it is 

 connected ; but passing between the. internal carotid artery and the 

 jugular vein, it curves forwards round the occipital artery, and then 



