322 THE RHOMBENCEPHALON. 



ii. Accessory (Motor Nerve). 



Cerebral Root. Nucleus ambiguus in Posterior lateral sulcus of medulla 

 closed medulla. below level of olive. 



Spinal Root. Nucleus in lateral part Lateral surface of cord between liga- 

 of base of anterior columna upper mentum denttculatum and poste- 

 five segments of cord. rior roots of spinal nerves. 



12. Hypoglossal (Motor Nerve). 



Nucleus under trigonum hypoglossi, Anterior lateral sulcus of medulla 

 floor of fourth ventricle, and in between pyramid and olive, 



closed medulla. 



Terminal Nuclei. The terminal nuclei of the first and second 

 cerebral nerves are peculiar and cannot as yet be classified with 

 the nuclei of other sensory nerves and sensory roots (Figs. 26, 

 43 and 63). The terminal nuclei of the fifth, the intermediate, 

 the eighth, ninth and tenth nerves may be called the posterior 

 columna series; because they are formed by masses of cell-bodies 

 representing the upward prolongation of the posterior columna 

 of gray substance in the spinal cord. Terminal nuclei are com- 

 mon sensory and special sensory. 



Common Sensory Nuclei (Fig. 96). Of the posterior columna 

 series of nuclei, the terminal nucleus of the fifth and of the tenth 

 nerves and a part of the terminal nucleus of the ninth nerve receive 

 common sensory impulses, and transmit them to the opposite thala- 

 mus by two routes, viz., through the medial fillet and through the 

 spino-thalamic tract. Impulses of the muscular sense travel over 

 the former route; those of the pain and temperature senses, over 

 the latter; and tactile impressions are believed to traverse both 

 routes alike. From the thalamus these impulses' are carried to 

 the cortex of the posterior central gyrus. Thus is the cortical 

 connection of these nuclei established; and each is brought into 

 reflex connection with motor nuclei by axones of the terminal 

 nuclei which run chiefly through the medial longitudinal bundle 

 and terminate hi the motor nuclei. 



Special Sense Nuclei. The cortical connection of the nucleus 

 tractus solitarii, which receives taste impulses from the glosso- 

 pharyngeal and intermediate nerves, has not been definitely traced ; 

 but it is probably relayed in the thalamus and is established by 



