344 THE INTERMEDIATE PRIMATES 



masses, the mesial surface only ot the entering;; nerve remaining uncovered by 

 nuclear material so that the trough arrangement of the nucleus about the 

 entering nerve stem is maintained. The dorsal cochlear nucleus, which is 

 situated dorsal to the triangular nucleus of Schwalbe of the vestibular com- 

 plex, is also relatively small and lies in contact w ith the lateral extremity of 

 the central gray matter oi the lloor ol the fourth ventricle. The strands of 

 gray matter connecting the \entral and the dorsal cochlear nuclei are also 

 poorly developed. 



The Colliculi 



The colliculi, which are situated in the tectum of the midljrain, appear 

 relatively well developed in the baboon. The superior colliculus is clearly 

 much more extensive than the inferior colliculus, the former being at least 

 three times the vertical height of the latter. The inferior colliculus arises 

 from the dorsal extension of the reticular formation at the point of junction 

 between the mesencephalon and the metencephalon. It is relatively incon- 

 spicuous and is separated from the larger superior colliculus by the inter- 

 collicular furrow, where the lateral extension of the reticular formation 

 comes to the surface of the stem. At its lateral and upper extremities the 

 inferior colliculus presents the beginning of the mferior brachuun which 

 passes from the inferior colliculus directly to the mesial geniculate body. 

 The inferior colliculus is continuous laterally with the reticular formation, 

 while dorsally it is continuous \vith the indifferent dorsal gray matter of 

 the mesencephalon. 



The superior colliculus arises, as does also the inferior, by a special- 

 ization in the tectum of the mesencephalon. It is in contact dorsally with 

 the indiflerent dorsal gray matter lying in the median line. Laterally it is 

 separated from the reticular formation by the development at this pomt of 

 the superior brachium which serves to connect the superior colliculus with 



