342 THE INTERMEDIATE PRIMATES 



of the posterior longitudinal faseieulus and the eircumfercntial reticular fiber 

 collections. 



The Pontile Nuclei 



In reconstruction, the pontile nuclei present an arrangement essentially 

 similar to that found in the lower lorms. The lormation of a superficial and a 

 deep layer connected at their mesial and lateral extremities by masses of 

 gray matter which represent the lateral and mesial buttresses is present also 

 in the baboon. The ventral and lateral surfaces of the pontile nuclei corre- 

 spond accurately with the surface anatomy of the pons itself. 



Mesially the mesial buttresses come into contact with one another at the 

 median raphe. Caudally the pontile nuclei arise in poorly developed arciform 

 nuclei which extend dow nward for a short distance upon the ventral surface 

 of the collected pyramidal tract. At the median line the mesial buttresses are 

 carried backward to come into contact with the ventromesial angle of the 

 reticular formation. A similar arrangement exists on the lateral aspect where 

 the lateral buttresses extend backward to become continuous with the ven- 

 trolateral angle of the reticular formation. Between these two points of con- 

 fluence, mesial and lateral, the deep layer of the pontile nucleus is separated 

 from the ventral surface of the reticular formation by the bay in which lies 

 the trapezoid body. 



The simple arrangement found in the low er forms is becoming more and 

 more complex and the interior of the pontile nucleus is found to be traversed 

 by numerous strands of nuclear material which pass from one side to the 

 other, breaking up the pallio-spinal and pallio-pontile systems of fibers into 

 smaller constituent masses. 



As the stem is followed upward, the deep layer of the pontile nuclei is 

 found to become directly continuous with the central portion of the sub- 

 stantia nigra, while the mesial and lateral portions of the substantia nigra 

 rest upon the mesial and lateral buttresses of the pontile nuclei. 



