336 THE INTERMEDIATE PRIMATES 



mass which is constantly shifted laterad by the opening of the fourth ven- 

 tricle until it overhangs, to a considerable extent, and almost obscures 

 from view the substantia gelatinosa trigemini. The nucleus of the 

 column of Goll reaches its maximum development at the le\cl where the 

 fourth ventricle opens and from that point it diminishes rather rapidly in 

 size. It is gradually obscured from view by the floor of the fourth ventricle 

 which approaches closely to the dorsal mass of the nucleus of the ci)Iumn 

 of Burdach, thus submerging the nucleus of the column of Goll. 



The nucleus of the column of Burdach continues upward to a level consid- 

 erably above the opening of the fourth ventricle, forming a part of the lateral 

 boundary of the ventricle. As a result of its lateral displacement it overhangs 

 the substantia gelatinosa trigemini. It rather abruptly diminishes in size and 

 disappears at about the mid-level of the inferior olivary nucleus. 



The substantia gelatinosa trigemini extends upward in the lateral 

 region of the ncuraxis, mcreasmg m all of its diameters to the mfcrior 

 olivary level where it is covered over by the lateral overhanging exten- 

 sions of the nucleus of the column of Burdach. It reappears embedded 

 in the reticular matrix between the ventrolateral nuclei of the reticular 

 formation and the nucleus of Deiters. At this level it undergoes a reduc- 

 tion which has been constantly found in this nucleus and which may be 

 termed the "waist of the trigeminal nucleus." From this point upward it 

 increases in size until its maximum is reached as the caput of the nucleus in 

 the mid-pontile level. It then suddenly undergoes reduction and disappears in 

 the upper pontile region where it presents on its mesial surface the rounded, 

 obliquely directed masticatory motor nucleus of the trigeminal complex. 



The Inferior Olivary Nucleus 



In the reconstruction of the inferior olivary nucleus there is evident a 

 considerable advance over that seen in the preceding forms. The ventral 



