RECOXSTRICTION OF TROGLOD^TES GORILLA r„r 



Lateral aiul dorsal to this eminence is a depressed area which indicates the 

 position of the dorsal vagal nucleus. 



The remainder of tlu' lloor of the inferior trianj^le of the fourth ventricU- 

 does not show any jxirticular modelling, while in the cephalic half of the 

 \ entricli- a delinitc- marking is found close to the midline. This represents the 

 position ol the nucleus abducentis and the longitudinal, subependymal por- 

 tion ol the seventh cranial ncr\c-. This elevation in the floor is the eminentia 

 teres. It is also know n as the emiiuntia facialis or abducentis. 



Lateral to this emmence is a marked prommence in the outer half of the 

 lloor ol the iourth \i'ntncle. Lying in the lateral recess, it extends for a short 

 distance both ce|)halad and caudad of the recess. It indicates the position of 

 the dorsal cochlear nucleus. 



As the mesencephalon is a])|)roacht(l the walls of the Iourth ventricle 

 rapidly contract, the root, lloor and lateral walls thicken and converge until 

 the gray matter bounding the fourth ventricle lorms a dense mass about the 

 central canal of the midbrain. In the mesencephalon the gray matter is drawn 

 forward \cntrall\ toward the rajihe and forms a longitudinal prolongation on 

 either side of the raphe. In this ventral prolongation appear the trochlear 

 and oculomotor nuclei. .AI)o\e the upper limit of the nucleus oculomotorius 

 the ventral prolongation of the central gray matter becomes more extensive. 

 Proceeding upward this jirocess becomes continuous with the gra\ matter 

 surrounding the third \eiUricle and w ith the median diencephalic nuclei. 



