LONGITUDINAL FIBERS OF PONS. 273 



the pars dor sails pontis in the formatio reticularis (Figs. 87 and 88). 

 They are dorsal to the corpus trapezoideum, and lie in the floor 

 of the fourth ventricle, where they are intermingled with the ven- 

 tricular gray substance. They do not form a compact layer, 

 but are collected into a number of distinct strands, of which the 

 larger are visible to the naked eye in Weigert-Pal sections. The 

 dorsal longitudinal fibers are mingled with many transverse and 

 oblique fibers; and, thus, there is produced the netlike arrange- 

 ment suggesting the name, formatio reticularis. The formatio 

 reticularis of the pons is continued down from the tegmentum 

 of the mid-brain and comprises the tegmental region of the pons. 

 The gray matter in the meshes of this network, which is the 

 stratum nucleare continued up from the medulla, contains the 

 nuclei of the fifth, sixth and seventh cerebral nerves and a part 

 of the nucleus of the eighth nerve, and also the nuclei of the for- 

 matio reticularis, viz., the nucleus centralis superior, medius 

 and inferior, and the nucleus lateralis medius. In the formatio 

 reticularis are the nine bundles or tracts of fibers that constitute 

 the dorsal longitudinal fibers of the pons. These tracts are as 

 follows : The anterior ascending cerebello-spinal tract, the spino- 

 thalamic tract, the medial fillet, the lateral fillet, the medial (pos- 

 terior) and anterior longitudinal bundles, the rubro-spinal tract, 

 the olivary fasciculus, and the descending root of the fifth cere- 

 bral nerve, besides unidentified fibers of the formatio reticularis 

 which are probably both ascending and descending in conduc- 

 tion. The anterior ascending cerebello-spinal tract and the 

 descending root of the trigeminal (or fifth) nerve are the only 

 tracts not already considered in our study of the tegmental region 

 of the mid-brain, page 156. 



(i) The medial fillet (lemniscus medialis, Figs. 87 and 88) 

 is a large bundle of fibers that runs through the pons next the 

 median plane. In the lower part of the pons it lies dorsal to the 

 trapezoid body, though some of the trapezoidal fibers pierce it. 

 Its origin is found on the opposite side in the nucleus funiculi 

 gracilis and nucleus funiculi cuneati and in the terminal nuclei 

 of common sensory cerebral nerves (Fig. 94). It conducts im- 

 pulses of the tactile and muscular senses. In the mid-brain it 

 18 



