305 



Similarly this ccllgroup in Ci'jptobranchiis ') can represent the 

 trochlear nucleus in a transitional stage between liic (h^rsal and 

 ventral position. 



The same cellgronp was fonnd in Nectnrns. In both animals this 

 group is not in contact with the Ill-nuclens, thus constituting a 

 striking contrast with Molge, where the IV-nuclens has not only 

 already attained its ventral position, but is also in close contact with 

 the III^ nucleus as can be easily demonstrated. 



Anatomy. — "Note on the size of the dorsal motor nucleus of the 

 X'h nerve in regard to the development of the stomach." By 

 Dr. H. A. Vermeulen Utrecht. (Communicated by Prof. Bolk). 



If one compares the shape of a frontal section through the medulla 

 oblongata in front of the calamus scriptorius in a horse, a cow, a 

 pig and a dog, one is struck by the difïerence. In the horse and the 

 dog the tloor of the 4''' ventricle is fairly level, whereas in the 

 cow and the pig it has acquii-ed the form of a split. 



In the latter the sideparts of the floor have a bulging character, 

 but in the horse it slopes down to the raphe, without any con- 

 siderable protrusion, and in the dog it is Jiearly Hat. With the 

 exception of the dog these differences remain the same more frontally. 

 The fossa rhomboidea of the horse is very long compared with the 

 cow's (horse 49 — 51 m.m., cow 34 — 35 m.m.), but in the former the 

 walls are less steep. 



Also in the pig the stem of the 

 brain is only short. In the dog 

 the floor of the ventricle deepens 

 again in frontal sections, but — 

 as I said — in caudal regions it 

 is very flat. These differences in 

 the shape of the fourth ventricle 

 appear to be related with the 

 extension and the form of the 

 nucleus motorius dorsalis vagi. 



and shorter. On the other hand also my measures and topography in my Rana 

 and Bufo have been controlled by Kappers, who found them to be right. 



Perhaps the difference between the two Ranae has to be explained hy the 

 possibility that in one case Rana fusca (mihi; and in the other case perhaps 

 Rana esculenta is used. 



1) Another argument for the probability that it may be considered as trochlear 

 nucleus is the fact that this lateral ccllgroup was not present in Rana, nor in Bufo. 



20 



Proceedings Royal Acad. Amsterdam. Vol. XVI. 



Equus 



Bos 



Sus scrofa dom. Oanis fam. 



Fig. 1. 

 Form of the IV ventricle (caudal). 



