THE GLOSSO-PHARYNGEAL NERVE. 



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medulla to the level of the nucleus gracilis. It lies immediately lateral to the lower 

 part of the median vestibular nucleus and the upper part of the hypoglossal nucleus, 

 its upper third being covered by the spinal vestibular nucleus and its lower third 

 overlying the hypoglossal nucleus. Its middle third corresponds to thefovea vagi 

 (Fig. 949) and comes into intimate relation with the ventricular floor. When 

 examined in cross-sections (Fig. 928) the nucleus appears prismatic in outline and 

 is seen to consist of subgroups of cells, of which the median contains the larger and 

 more conspicuous elements and corresponds to the dorsal motor nucleus. The 

 remaining groups, the dorsal sensory nucleus, are composed for the most part of 

 small irregular and often spindle cells, that receive end arborizations of afferent fibres. 



The nucleus ambiguus (nucleus ventralis) consists of an ill-defined slender 

 column of large multipolar cells, which extends from the level of the entrance of the 

 cochlear nerve at the upper border of the medulla to about the level of the beginning 

 of the pyramidal decussation, and 

 is best developed in its upper part. 

 In transverse sections of the 

 medulla (Fig. 927), the tract is 

 distinguishable within the formatio 

 reticularis grisea, midway between 

 the dorsal accessory olivary 

 nucleus and the substantia gelati- 

 nosa, as a small and inconspicuous 

 group of cells. Arising as axones 

 of the latter, the loosely grouped 

 motor fibres at first pass dorsally 

 to the vicinity of the ventricular 

 floor, then bend sharply outward, 

 and, as in the case of the vagus, 

 join with the similar fibres proceed- 

 ing from the dorsal motor nucleus 

 to form the emergent root strands. 



The Sensory Nuclei. 

 The nuclei receiving the afferent 

 fibres of the lateral mixed nerves 

 in question include the sensory 

 part of the dorsal nucleus (nu- 

 cleus alae cinereae), above de- 

 scribed, and a tapering column of 

 gray matter, the spinal nucleus 

 (nucleus tractus solitarii), which 

 resembles the corresponding 

 nucleus of the trigeminus. The 

 spinal nucleus is closely associated 

 with a conspicuous longitudinal 

 tract of caudally directed fibres, 

 the fasciculus solitarius 

 (tractus solitarius), so called on account of the apparent isolation of the bundle when 

 viewed in transverse sections (Fig. 927). That such, however, is not the case is 

 evident when the fact is recalled that the fibres which turn downward to form the tract 

 are accompanied by the spinal nucleus of reception, around whose cells they end. The 

 fasciculus solitarius extends from the upper border of the medulla to the level of the 

 lower limit of the decussation of the fillet and is related to the sensory fibres of three 

 nerves. The first of these, the facial, contributes only a limited number of fibres that 

 occupy the uppermost part of the bundle ; the second, the glosso-pharyngeal, forms by 

 far the largest constituent of the fasciculus ; whilst the third, the vagus, adds fibres 

 that course within the lowest segment of the tract. 



Diagram showing connections of root-fibres of glosso-pharyngeal 

 and pneumogastric nerves and of sensory fibres of facial ; sensory 

 fibres are black, motor ones red; VII, geniculate ganglion; IX, 

 A", ganglia of ninth and tenth nerves; DN, dorsal nucleus; FS, 

 fasciculus solitarius, accompanied by column of gray matter; NA, 

 nucleus ambiguus; AcV, accessory vagus (bulbar portion of AY); 

 MF, median fillet. 



Central and Cortical Connections of the Motor Part of the Glosso-Pharyngeal Nerve. 

 The motor fibres of the glosso-pharyngeal nerve are the axones of the motor neurones situated 



