846 MAN 



the rcniainder ol the mass appearing as an indisenmniate, undillerentiated 

 nuelear matrix. 



The dorsal surlaec ol the retieuhir formation eomes into intimate rela- 

 tionship with, and its eonformation is greatly iniluenced h\ the substantia 

 gelatinosa trigemmi, the lloor of the fourth ventriele, and the numerous 

 nuelear eollections which appear in this vieinity in eonneetion with thiM)rigin 

 and termination ol many of the cranial nerves. In the lower jjart of the pons 

 the reticular formation is much reduced in thickness, the deep layer of the 

 pontile nucleus being separated from the floor of the fourth ventricle l)\- only 

 a small amount of reticular formation. In this region the libers underlying the 

 lloor of the ventricle form a considerable condensation limiting the dorsal 

 extent of the reticular formation and reduce the gray reticular formation to a 

 body of relatively small dimensions. In the mid-portion of the pontile teg- 

 mentum, however, the reticular formation increases m thickness and is dis- 

 posed as a more or less transverse quadrilateral mass presenting a smooth 

 median surface almost m direct contact with tlu' raphe. The development m 

 this region of the trapezoid body and the lateral fillet serves to differentiate 

 the more mesial portion of the reticular lormation into a thicker dorsal sub- 

 di\ision in contact with, or separated by only a small amount of white matter 

 from, the lloor of tlu' fourth \entricle, and a thin lamina of gray mattt'r which 

 develops ventrallx in contact with the |)ontile nucleus. Laterally in the mid- 

 ])ortion of the pons, these two sul)di\ isions ol the reticular lormation |om, 

 the point of junction corresponding to the lateral extri'inity ol the lloor ol 

 the fourth ventricle. 



Still further laterall\ a thm edge ol the reticular lormation works out- 

 ward and backward, insinuating itself betwA'cn the surlaec ol the brain stem 

 and the superior cerebellar pedunele, which as it lea\es the roof of the ft)uit li 

 ventricle turns forward, upward and inward in a spiral course toward the red 

 nucleus of the opposite side which is situated in the \entral pc)rti()n ol the 



