AREAS OF THE MEDULLA OBLONGATA 



881 



between the olivary and medial accessory olivary nuclei, sometimes mesad of the 

 latter, to emerge between pyramid and o/.ve. None of the fibres decussate across 

 the middle line, but the nuclei are coordinated by commissural fibres. Axones 

 from cortical cells (ventral third of precentral gyre) terminate in relation with the 

 cells of the hypoglossal nucleus. 



The hypoglossal nucleus permits of subdivision into groups: (a) a medial and 

 (6) a lateral sub-group. The lateral group innervates the Palatoglossus and 

 Pharyngoglossus, while the medial nuclear group innervates the remainder of the 

 tongue muscles (Lingualis trans versus and inferior, Genioglossus and Hyoglossus). 



The Spinal Accessory Nerve Nucleus. The spinal accessory nerve is also a purely 

 motor or efferent nerve whose axones arise from an attenuated nucleus, with 

 large multipolar cells, in direct continuation with the nucleus ambiguus (of the 



CERVICAL NERVES ' 



FIG. 647. Nuclei of oriein of the cranial motor nerves schematically represented in a supposedly 

 transparent brain stem, lateral view. 



ninth and tenth nerves) cephalad, and with the dorsolateral cell column of the 

 ventral horn of the upper five or six segments of the cord. The oblongatal portion 

 of the nucleus gives rise to the encephalic root of the accessory nerve and its axones 

 join the vagus to innervate the laryngeal muscles. Hence it may also be termed 

 the nidus laryngei (in contradistinction to the nidus pharyngei or nucleus ambiguus, 

 whose axones join the vagus and glossopharyngeal nerves to be distributed to 

 the pharynx). The ventrolateral division of this cell column is believed to be 

 the cardioinhibitor centre. The axones from the spinal nucleus are distributed 

 to the Trapezius and Sternomastoid muscles. 



The nucleus of the spinal accessory nerve is likewise under the dominion of the 

 cerebral cortex by way of the pyramidal tract, and a reflex arc is completed by 

 afferent axones from the dorsal roots of the spinal nerves. 



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