The Lower Portion of the Human Brain-Stem. 73 



two dorsal projections is the main concavity of the surface of each side. 

 This becomes less marlced as one goes cephalad. The surface is irregular!}^ 

 fissured and furrowed, showing between these groovings many small dorsal 

 projections. 



The relations of the dorsal end of the lateral plate of the pontine com- 

 plex with the nucleus of the nervus trigeminus are worthy of comment. On 

 a level with the superior pole of the nucleus nervi facialis the lateral plate 

 of the pons projects dorsally and meets the substantia gelatinosa just as that 

 merges into the sensory enlargement (figure 4). This projection of tissue 

 from the nuclei pontis lies mesial to the lateral wall of the complex and the 

 lateral cell-mass overhangs it. The separation of the nuclear material from 

 the pontine nuclei and that composing the trigeminal complex is very diffi- 

 cult. Traced cephalad from the caudal point of union of the trigeminal 

 luicleus and the pontine nuclear material, the connection between the dorsal 

 l)ontine mass lying mesial and ventral to the trigeminal nucleus is broken 

 for a considerable extent. This is shown in figure 2. The dorsal mass of 

 pontine cells projects in a laterally directed ridge and then suddenly recedes 

 as the connection is again made at the upper extremity of the model. Here 

 the connection between the dorsal pontine mass and the lateral wall of the 

 nuclei pons is tjuite massive. On mesial view the dorsal pontine mass is 

 seen to extend quite a distance dorsally toward the mesial eminence on the 

 surface of the fifth nucleus. 



The nucleus reticularis tcgmcnti pontis (Flcchsig) is the dorsal projection 

 of the mesial portion of the dorsal surface of the nuclei pontis. It really 

 represents a portion of the nuclei pontis lying along the mid-line of the 

 tegmentum and projecting dorsally almost beneath the floor of the fourth 

 ventricle (figure 14). Its mesial outline is shown in the transparenc.y of figure 

 4 as the irregular continuation of the dorsal surface outline of the pontine 

 nuclei. As modeled, the nucleus shows two distinct portions, a marked 

 laterally projecting mass, irregular in extent and marked by a bizarre surface, 

 situated midway between the dorsal surface of the nuclei i)ontis and the 

 floor of the fourth ventricle, and a second dorso-lateral projection beneath 

 the nucleus incertus in the floor of the ventricle. These two masses are 

 connected by a broad irregular bridge of nuclear material. The more ventral 

 of these two masses shows a gradual increase in extent as it proceeds cephalad ; 

 at its caudal portion it is marked by a deep cei)halo-caudal furrow. It 

 continues beyond the cephalic limit of this model. Its surface is marked 

 by many irregularities, especially by deep fissures. The dorsal of th(> two 

 masses projects dorso-laterally as a bizarre and heavy cell-column, which 

 shows a peculiarly shaped triangular caudal projection (figure 4) . The dorsal 

 surface curves laterally and dorsally beneath the nucleus incertus. This 

 spur recedes as it goes cephalad and, after a marked notch, a second dorso- 

 lateral spur takes its place beneath the nucleus incertus. This terminates 

 as the superior margin of the model is reached (figure 4). 



