124 THE LOWER PRIMATES 



trochlear decussation is reached. In other words, the bulbopontile sulcus 

 holds a much more cephalic position than in other species. It is even higher 

 than in the cat and most rodents. This position of the sulcus clearly indicates 

 the inferior development of the pons VaroHi. The internal pontile structure, 

 however, does not depart from the type of organization characteristic of it 

 elsewhere. In it may be discerned the three typical strata. A pecuharity 

 in their arrangement is the fact that the stratum superlicialc does not, as in 

 other species of primates, appear as the most caudal element in the pons. 

 Fibers from the stratum complexum make their way across the stem in the 

 direction of the middle cerebellar peduncle before there is evidence of the 

 more superficial transverse axons. This gives rise to an unusual appearance, 

 in that the pyramid maintains its ventral position m the stem although pon- 

 tile fibers are ah'cady present. It is usually the case that in the caudal por- 

 tion of the pons, superficial transverse fibers cross in front of the pyramid and 

 thus exclude the latter from a position on the surface. This arrangement of 

 fibers makes the pyramid in tarsius appear much longer than in other species, 

 while the pons is actually much shorter. Nor is the peculiarity of the pontile 

 fibers limited alone to this late appearance of the superficial stratum. Such 

 decussation as the pontile fibers do make, exerts a feeble influence upon the 

 long suprasegmental systems. The pyramid, for example, which in all other 

 primates becomes separated into more or less scattered bundles, shows little 

 of such tendency in tarsius. The manner in which the pyramidal system 

 maintains its integrated constituency and seems in this way to force the 

 pontile fibers to sweep around rather than through it, is another fact 

 emphasizing the low organization of the pons Varolii in tarsius. 



The marked tendency of the mesial fillet to stretch out transversely in 

 the pons so as to form the boundary between the tegmentum and the basis, 

 is almost entirely absent in tarsius. The fillet maintains its position relatively 

 near the median line, where it appears as a dense bundle. All of these phenom 



