278 THE RHOMBENCEPHALON. 



caeruleus, and runs between it and the superior end of the ter- 

 minal or sensory nucleus. 



In the lowest part of the pons there is seen the spinal tract of 

 the fifth nerve (tracus spinalis nervi trigemini). This is a part 

 of its sensory root and is composed of the descending limbs of 

 T-branched axones from the semilunar ganglion (Gasseri). The 

 spinal tract of the trigeminal nerve runs lateral to the gray sub- 

 stance, between the substantia gelatinosa (Rolandi), on the inner 

 side, and the vestibular root of the acustic nerve and the resti- 

 form body on the outer side. 



GRAY MATTER OF THE PONS. 



In the pons gray matter is found in two situations: (i) In 

 the interstices between the deep transverse fibers of the pars 

 basilaris pontis and the ventral longitudinal fibers, the nuclei 

 pontis; and (2) in the formatio reticularis, just under the fourth 

 ventricle where it forms the stratum nucleare. 



The nucleus pontis is a mass of gray matter, on either side 

 the raphe, containing the bodies of large multipolar nerve cells 

 whose axones run through the brachium pontis of the cerebellum 

 to the cortex on the opposite side. It extends vertically throughout 

 the pons and is continuous with the arcuate nucleus of the medulla. 

 The nucleus pontis receives the terminals of the descending tracts 

 which form the inner and outer fifths of the basis pedunculi and 

 the intermediate bundle of the same, and thus connects these 

 tracts with the cerebellum. It forms a relay in the indirect motor 

 path. 



The gray matter of the stratum nucleare includes (i) the 

 olivary group of nuclei, viz., the superior olivary nucleus, the 

 nucleus of the corpus trapezoideum, the preolivary nucleus and 

 the semilunar nucleus; (2) the nuclei of the formatio reticularis, 

 viz., the nucleus centralis superior, medius and inferior, and the 

 nucleus lateralis medius; and (3) the nuclei of cerebral nerves 

 the fifth, sixth and seventh, and a part of the vestibular nucleus 

 of the eighth nerve. 



(i) Olivary Group. The superior olivary nucleus (n. olivaris 



