RECONSTRUCTION OF TARSIUS SPECTRUM 145 



The Vestibular Nuclei 

 A relatively short distance above the opening of the fourth ventricle 

 there appears a specialization in the reticular formation which hcs between 

 the nucleus of Burdach and the iloor of the fourth ventricle. This specializa- 

 tion consists of groups of fibers, rather loosely arranged in a matrix of gray 

 matter, thus presenting the typical appearance of the nucleus of the descend- 

 ing root of the vestibular complex. This mass of gray matter enlarges in size, 

 and very soon assumes tlie characteristic arrangement of the nucleus of 

 Deiters. As it increases in size, the nucleus of Burdach coriTspondingly 

 decreases, and as the nucleus of Burdach comes to an end, the nucleus of 

 Deiters assumes its full proportions. In tarsius the nucleus of Deiters is a 

 relatively large collection of gray matter, and occupies the outer third of the 

 dorsal portion of the tegmentum directly ventral to the floor of the fourth 

 ventricle. As the nucleus of Burdach terminates, the nucleus of Deiters comes 

 to the surface and appears on the dorsolateral aspect of the neuraxial tegmen- 

 tum. The increase in size of the gray matter in this region shows a very defi- 

 nite effect upon the ascending nucleus of Rolando which is displaced to a 

 distinctly ventral position by the increasing mass of the Deitersal complex. 

 The nucleus reaches its maximum proportions at a point somewhat above 

 the mid-ventricular level where, in its mesial portion, there develops a small 

 area somewhat more homogeneous in appearance, which is the triangular 

 nucleus of Schwalbe. This nucleus forms part of the lateral wall of the ven- 

 tricle underlying the ependymal floor and is in contact laterally with the 

 Deitersal complex. At this point there appear the cochlear nuclei in connec- 

 tion with the entrance of the cochlear roots, and the dorsal cochlear nucleus 

 overlies the nucleus of Deiters, hiding it from view. Having assumed its 

 maximum proportions, the nucleus of Deiters rapidly diminishes and disap- 

 pears, giving place to a rather large collection of reticular substance situated 

 lateral to the central gray matter. As the nucleus of Deiters approaches the 



