RECONSTRUCTION OF TARSIUS SPECTRUM 147 



larger than the inferior colliculi. The inferior collieuli ap])ear at the dorso- 

 lateral angle of the brain stem at first as small rounded collections of gray 

 matter. These expand enormously in succeeding sections, rapidly assuming 

 their maximum proportions. They are situated lateral to a dorsal prolonga- 

 tion of the central gray matter. Thej' are roughly oval in outline, the axis 

 being directed somewhat from before, backward and inward. Having rapidly 

 assumed their greatest dimensions, the colliculi continue upward for a short 

 distance and then begin to contract. They are in relation laterally with a 

 prolongation of the reticular formation which arises in the dorsolateral angle 

 of the tegmentum, and sweeps around the colliculi sending a prolongation 

 upward to interpose itself between the upper limits of the inferior colliculus 

 and the lower limits of the superior colliculus. The colliculi are suppcjrtcd 

 vcntrally by the reticular formation and mesially by the gray matter of the 

 central formation. As seen in the cross sections the inferior colliculus corre- 

 sponds fairly accurately \\ ith the general conformation of the inferior col- 

 liculus in the whole primate series, being represented chiefly by a core of 

 white matter, upon \\hich are superimposed successive layers of white and 

 gray matter. The superior colliculus, however, presents a very different 

 appearance, having a typical cortex with a core of medullary substance. The 

 superior colliculus makes its appearance slightly above the point of termina- 

 tion of the inferior colliculus, as a small, dorsomesially situated mass of gray 

 matter. This rapidly enlarges in size, spreading laterally and presenting a 

 ventral prolongation which continues forward laterally along the outer aspect 

 of the dorsal portion of the brain stem. Central to the superior colliculus, 

 there appears a prolongation of the reticular formation dorsally around the 

 central gray matter which is situated in the center of the reconstruction. As 

 the superior colliculus is followed upward it assumes greater and greater 

 proportions, becomuig considerably thicker, and presents a very definite 

 plateau-like appearance on its dorsal aspect, which turns at a sharp angle 



