378 



PHYSIOLOGY 



(a) The hypoglossal nerve. 

 (6) The sixth nerve. 



(c) The fourth nerve. 



(d) The third or oculo-motor nerve. 



(2) Splanchnic Sensory Nuclei. Immediately outside the column of 

 motor cells is a column of grey matter which receives the terminations of 

 the afferent fibres belonging to the ninth, tenth, and eleventh nerves, and 

 is sometimes called the vago-glossopharyngeal-accessory nucleus. This grey 



FIBRES TO NUCL.LEMNISCI 

 ^CORPORA QUAORIGEMINA 



. PYRAMID 



NERVE-ENDINGS 



,N ORGAN OF CORTI 



FIG. 193. Plan of the course and connections of the fibres forming the cochlear 

 root of the auditory nerve. (SCHAFER.) 



r, restiform body ; V, descending root of the fifth nerve ; tub.ac, tuberculum 

 acusticum ; n.acc, accessory nucleus ; 8.0, superior olive ; n.tr, nucleus of trape- 

 zium ; n. VI, nucleus of sixth nerve ; VI, issuing root-fibre of sixth nerve. 



matter of course does not give rise to the fibres of these nerves which, like 

 other sensory nerves, are axons of ganglion-cells lying outside the central 

 nervous system. 



(3) Splanchnic Motor Nuclei. These lie more deeply at some distance 

 from th'e middle line, and include the nucleus ambiguus for the efferent fibres 

 of the vaso-glossopharyngeal, the nucleus of the seventh or facial nerve 

 (originally splanchnic or branchial, now typically somatic), and the motor 

 nucleus of the fifth nerve with its prolongation into "the mid-brain. 



(4) Sensory Somatic Nuclei. The chief representative of this group 

 is the great sensory root of the fifth nerve. The fibres of this nerve arise 

 from the Gasserian ganglion, pierce the fibres of the pons Varolii, and run 

 to the dorso-lateral part of -the pons, where they divide into ascending and 

 descending fibres. These fibres form a cap to the substanfria gelatinosa, 

 the descending branches, which are longer, being conspicuous in sections of 

 the medulla as low down as the first or second cervical nerve. This nerve 

 gives common sensation to practically the whole of the head. 



It is doubtful in what group we should place the fibres of the eighth 

 nerve. This nerve really consists of two parts very different in function, 

 the cochlear or auditory nerve, and the vestibular or labyrinthine nerve. 



