GRAY MATTER OF MEDULLA. 307 



nucleus lies along the ventro-medial surface of the restiform body; 

 it enlarges in bulk and approaches the surface near the middle 

 of the medulla, where it produces the tuberculum cinereum; 

 and it is then continued down into the cord as a cap of the poste- 

 rior columna of gray substance. In the lower part of the medulla 

 the nucleus underlies the visible part of the tractus spinalis nervi 

 trigemini. 



The sensory root of the trigeminal nerve (fifth) enters the pons 

 on its ventral surface, in line with the roots of the seventh, eighth, 

 ninth, tenth and accessory nerves (Fig. 85). The root fibers divide 

 T-like; the short ascending branches end in the pontine nucleus 

 of the fifth nerve and the long descending branches, forming the 

 spinal tract, terminate in the nucleus of that tract. A certain few 

 of these root-fibers go directly to the motor nucleus of the trigemi- 

 nal nerve and perhaps to other motor nuclei; these are reflex in 

 function. 



From the trigeminal nucleus axones establishing reflex and cor- 

 tical relations run : (a) To motor nuclei by way of the medial long- 

 itudinal bundle and directly without entering that bundle, forming 

 the middle link of reflex arcs, and (b) by way of two paths they 

 run toward the cerebral cortex as far as the thalamus. The latter 

 cross the median raphe and probably enter the medial fillet and 

 the spino-thalamic tract. The axones bearing impulses of the 

 muscular sense enter the medial fillet and are continued through it 

 to the lateral nucleus of the thalamus; those fibers which conduct 

 pain and temperature impressions run through the spino-thalamic 

 tract to the same nucleus. Both sets of fibers conduct tactile im- 

 pulses. From the thalamus the cortical fillet completes the path 

 to the somaesthetic cortex of the cerebrum. 



Vestibular Nuclei (Nn. Nervi Vestibularis, Figs. 92 and 93). 

 These are located partly in the pons as already pointed out, and 

 extend as low as the mid-medulla. Their function is equilibrium. 

 The principal micleus (Schwalbe's) is dorso-medial in position 

 and lies beneath the acustic area of the ventricular floor, crossed 

 by the medullary striae. It extends transversely from near the 

 eminentia medialis almost to the restiform body. It appears 

 to receive nearly all the fibers of the vestibular nerve, which arbor- 



