661 



degree than before; the centrum remains poor in cells. This pi'ocess 

 repeats itself for a third time; then practically all cells disappear, witii 

 the exception of the dorso-lateral portion and the connecting bridge 

 witli the X dorsalis; a few commissural cells still occur occasionally. 

 In the calamus the grouping is different; the medial and dorso-lateral 

 groups merge into an elongated triangular whole, the apex of which 

 points ventroiateraüy ; ventrally from this lie the ventro-medial and 

 the ventro-lateral grou|)s, now fairly well on the same level (tig. 18). 







^ > 



■4 I , 





Fig. 18. 

 Also in this region of the tongue nucleus a few cells can be observed 

 in the raphe; they no longer show, liowevei', the striking hypo- 

 glossus type, but have become much smaller. The former group is 

 of the same shape as the nucleus hypoglossi in other animals, 

 triangular in form and with a majority of large cells, it lies medially 

 under the ependyma of the fourth ventricle; the ventral groups are 

 different, occasionally they converge so that we see a second tongue 

 nucleus ventrally from the usual tongue nucleus, built up of a 

 fairly broad horizontal row of cells, the cell-type of which has 

 grown smaller than of that lying dorsally (fig. 19) ; in general, 

 however, the ventral tongue nucleus consists of a medial and a 

 lateral portion. Between the lateral portion and the dorsal tongue 

 nucleus we often tlnd a few large XII cells (tig. 19); not in)fre- 



