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in inainnuxliaii embryos and IV Ramon in birds, reptiles and amphi- 

 bians. 



We are now accustomed to apj)Iy lo all these cells the name of 

 iiucl. mesencephalicus tru/enimi, although the name employed by 

 Wallenburg and Edingkk of iiiicJ. riKKjnocdluJaris tecli mioht be a 

 better one. 



Considering, however, that it is from (he complex of these cells 

 that in any case the tibre bundle which is generally named radir 

 we.'iencephalica trigemini, originates, and the cell group itself cainiol 

 evidently be divided into sub-groups, there can be no objection for 

 the present to homologise the said elements of the ditferent species 

 of animals. 



As a necessar}' preparation for forming an opinion concerning the 

 physiological signiticance of the mesencephalon nucleus and root, 1 

 devoted my attention in particular to determine the position of the 

 cells in proximo-distal direction and the manner in which the root- 

 fibres leave the brain-stem. Foi- the detailed account of my results 

 (lists of cell-enumerations) I refer to (he above-mentioned article 

 shortly to be published, Init I may give here the chief facts, illustrated 

 by tigures. 



Fishes. In all non-mammalian vertebrates, the mesenc. quintus- 

 cells are realh^ confined to the mid brain, as their name implies. 

 The oral beginning of the nucleus falls on the level of the commis- 

 sura posterior, the most caudal cells reach to the cross plaiies of 

 the trochlear nucleus. One very striking excei)tion to this rule is 



found in the teleostei (fig. 2). If the position 

 of the nucleus in these animals be compared 

 to that in selacldi (fig. 1), two points are 

 noticeable. 



In the first place, the position of the cells as 

 found in selachii (scyll. canic, acanth. vuhj., 

 iinistehis vulg., irija clavata), dorsally to the 

 aqueductus Sylvii, or to the lateral corners 

 Fig. 1. Scyllium canicula. of this, is deviated from, and moreover these 

 cells in teleostei (lophius piscatorius, gadus morrhua, hippoglossus, 

 nbramis, trutta) lie much closer together and form a nerve nucleus 

 in the more usual meaning of the word. They are to be found 

 immediately fVonto-ventrallj', and further ventrally. to the venti-iculus 

 lobi optici, which in these animals is more clearly developed than 

 in the selachii; thus, widi i-egard (o (he brain-stem as a whole, 

 they keep their |)Osi(ion widiin (he doi'sal j)ar(, wi(h a (endency 

 in the direction of (he (egmentuni. (^uile in accordance with the 



