GRAY MATTER OF THE PONS. 281 



(3) Nerve Nuclei. The nuclei of the trigeminal nerve (nuclei 

 nervi trigemini) are two in number. The genetic or motor nucleus 

 of the fifth nerve (n. motorius} in the pons is a continuation of the 

 mesencephalic nucleus. It is rather close to the fourth ventricle 

 in the extreme lateral part of its floor, underneath the locus cseru- 

 leus (Fig. 86). It extends as far down as the middle of the pons, 

 where the whole group of axones passes forward into the motor 

 root of the nerve. Cortical Connection. The nucleus receives 

 motor fibers from the opposite pyramidal tract and perhaps from 

 the cerebro-pontal tracts of the same side; and sensory fibers 

 terminate in it from the sensory root of the fifth nerve, and 

 from the terminal nuclei of other common sensory nerves, through 

 the medial longitudinal bundle and establish its reflex connections. 



The terminal or sensory nucleus (n. terminalis or sensibilis) 

 of the trigeminal nerve begins at the middle of the pons and 

 extends to the second segment of the spinal cord. At its superior 

 end it is ventro-lateral to the motor nucleus and under cover of 

 the brachium conjunctivum of the cerebellum (Figs. 86 and 87). 

 Near the medulla it lies ventro-medial to the restiform body and 

 the vestibular root of the acustic nerve. This part of it is almost 

 in contact with the nucleus of the facial nerve, and its distance 

 from the ventricle is greater than it is higher up. The nucleus 

 is gelatinous in character and is continuous with the same substance 

 in the posterior columna of the spinal cord. It receives the 

 whole sensory root of the trigeminal nerve. Just lateral to it 

 runs the spinal tract of the fifth nerve, the fibers of which gradually 

 bend into the nucleus and terminate in rich arborizations. Axones 

 from the nucleus pursue several different courses: (a) Reflex 

 fibers go directly to the motor nucleus of the fifth and through the 

 medial longitudinal bundle to other motor nuclei, (b) Tactile, 

 pain and temperature fibers are supposed to enter the opposite 

 spino-thalamic tract through which they reach the thalamus; 

 perhaps, some run through the anterior cerebello-spinal tract 

 to the cerebellum, (c) Tactile and muscular sense fibers pro- 

 ceed to the thalamus, probably through the medial fillet on the 

 opposite side. 



Nucleus of the Abducent Nerve (N. Nervi Abducentis). This 



