138 THE LOWER PRIMATES 



distance above the point at which the nuclei of Rolando begin to diverge one 

 from the other. The nucleus appears on cither side of the midline as a small 

 protrusion of gray matter from the dorsal surface of the central gray matter. 

 These rehitively insignificant dorsal protrusions He close to the midline and 

 increase very slightly in size as they continue upward. As the opening of the 

 fourth ventricle is approached, these nuclei assume somewhat larger propor- 

 tions and form a part of the lateral wall of the ventricle, extending laterally 

 but never raising themselves to any extent from the surface. The nuclei oi 

 Goll continue upward to a point only slightly above the opening of the fourth 

 ventricle in the lateral ventricular wall, and come to a rather abrupt 

 termination. 



The nucleus of Burdach appears at a higher level than the nucleus of 

 Goll, as a Hat sessile elevation on the dorsal surface of the central gray matter 

 lateral to the nucleus of Goll. It slowly but gradually increases in size, diverg- 

 ing rather markedly from its fellow of the opposite side as the fourth ven- 

 tricle opens. It extends upward to about the midventricular level. In the 

 upper portion of its course it arrives at a certain degree of independence from 

 the wall of the ventricle and rises dorsally to a moderate degree in a well- 

 marked prominence in the dorsolateral angle of the brain stem. It rather 

 suddenly terminates and its place is taken by the nuclei of the vestibular 

 complex. 



The substantia gelatinosa Rolandi continues upward as a direct pro- 

 longation of the substantia gelatinosa of the spinal cord into the medulla 

 oblongata. These two ULiclei show the first indication of the opening of the 

 fourth ventricle by their divergence one from the other, thus allowing the 

 central gray matter to approach the dorsal surface of the oblongata. Con- 

 tinuing to diverge, the nuclei assume considerable lateral proportions, are 

 supported directly on their mesial aspect by the reticular formation, and 

 finally reach the lateral meridian of the brain stem. From this point they 



