i88 THE LOWER PRIMATES 



dach, the central gray matter and the reticular formation at the dorsolateral 

 angle of the latter. The large nucleus of Deiters first appears at the 

 lower decussational level of the pyramidal tract and, rapidly expandmg, 

 reaches its greatest diameter at the midventricular level of the brain stem. 

 From this region it diminishes as higher levels are approached. As it 

 diminishes in bulk the vestibular nuclei increase to their maximum and then 

 recede to give place to the cochlear nuclei. At the midventricular level the 

 nucleus of Deiters and the nucleus of Schwalbe both begin to diminish. The 

 vestibular nuclei are carried upward about the lateral walls of the ventricle 

 by the small nucleus of von Bechterew which is so poorly diflerentiated as 

 to make adequate representation in this model impossible. 



The Cochlear Nuclei 



As shown in the reconstruction, the cochlear complex consists of both 

 the ventral cochlear nucleus and the dorsal cochlear nucleus which are situ- 

 ated directly ventral to the subependymal gray matter of the floor of the 

 lateral recess of the fourth ventricle. The dorsal cochlear nucleus is situated 

 in the lateral ventricular recess and is more or less oval in outline. It extends 

 for a short distance above and below the limits of the lateral ventricular 

 recess. It also extends mesially for a short distance under the ventricular 

 gray matter. 



The Substantia Nigra 



The reconstruction of this mass of gray matter resembles the nucleus 

 found in lemur. It appears to be continuous with the deep layer of the pontile 

 nuclei, supported throughout its entire transverse extent by this lamina, 

 while at its extremities it rests upon the lateral and mesial buttresses of the 

 pontile nuclei. Mesially it is connected with its fellow of the opposite side by 

 the undifferentiated ventral interpeduncular gray matter. In its lateral por- 



