646 STRUCTURE OF THE BULB, PONS, AND MID-BRAIN [dl. XLIY. 



by two distinct origins one from a centre in the floor of the fourth 

 ventricle, and connected with the glosso-pharyngeal-vagus-nucleus ; 

 the other, from the outer side of the anterior cornu of the spinal cord 

 as low down as the fourth cervical nerve. The fibres from the two 

 origins come together at the jugular foramen, but separate again into 



FIG. 469. The tenth and twelfth nerves, pyr, pyramid ; n.XII., nucleus of hypoglossal ; XII., fibre of 

 hypoglossal; d.n.X.XL, combined nucleus of vagus and spinal accessory; n.amb., nucleus 

 am biguus ;/.., fasciculus solitarius, descending fibres of vagus and glosso-pharyngeal ; f.s.n., its 

 nucleus; X., motor fibre of vagus ; g, ganglion cell in vagus trunk giving rise to a sensory fibre; 

 d.V., descending root of the fifth nerve ; r, restiform body. (Schafer.) 



two branches, outer and inner. The outer, consisting of large 

 medullated fibres from the spinal origin, supplies the trapezius and 

 sterno-mastoid muscles. The inner branch, consisting of small 

 medullated fibres from the medulla, supplies chiefly viscero-motor 

 filaments to the vagus. The muscles of the larynx, all of which are 

 supplied by branches of the vagus, derive their motor nerves from the 

 accessory ; and (which is a very significant fact) Vrolik states that in 

 the chimpanzee the internal branch of the accessory does not join the 

 vagus at all, but goes direct to the larynx. The crico-thyroid, how- 

 ever, receives fibres which leave the bulb by glosso-pharyngeal 

 rootlets; whether it receives spinal accessory fibres as well is 

 uncertain. 



The twelfth nerve (hypoglossal) is also entirely efferent. It arises 

 from a large celled and long nucleus in the bulb, close to the middle 

 line, inside the combined nucleus of the ninth, tenth, and eleventh 

 nerves. It receives numerous collaterals from adjacent sensory 

 tracts, and from the descending nuclei of the fifth, ninth, and tenth 

 nerves, and from the posterior longitudinal bundle. Fibres from this 

 nucleus run from the ventral surface through the reticular formation 



