256 Journal of Comparative Neurology. 



several spinal nerve roots. These form a plexus where the fibers 

 join which belong together. The cell-bodies for one muscle of 

 the spinal segments are usually scattered through several seg- 

 ments. In the facial, abducens and hypoglossal nuclei we find 

 the cells of one type grouped together and the intermediate 

 cells (for the ground-bundles) very probably outside of the 

 group, in the reticular substance ; in the spinal cord the motor 

 cells are less closely grouped ; the intermediate cells are to 

 some extent scattered among them. The best places for a study 

 of the cell-bodies of the motor neurones are therefore the cra- 

 nial nerves mentioned, the best one of all the abducens, because 

 there is hardly any objection to be met to the trio : one nest 

 of nerve-cells, one nerve and one muscle. This apparatus is 

 studied and pictured by von Gudden (Abhandlungen, Plate XL, 

 Fig. 11). In the following I shall refer to the hypoglossal mo- 

 tor neurones, partly because of the possibility of referring to 

 the figures of Forel, partly because I make use of material ob- 

 tained experimentally by myself. We see large cells forming a 

 group on either side of the raphe in the floor of the fourth ven- 

 tricle within its posterior segment (behind the point from which 

 the striee acusticae emerge). From these ' nuclei ' bundles of 

 fibers arise which run at first parallel to the raphe and then leave 

 the medulla between pyramid and olive, to form the hypoglos- 

 sal nerve, which can be followed into the muscles of the tongue. 

 It is our first duty to prove that these cells are really all in 

 connection with the fibers mentioned and that all the fibers of 

 the hypoglossal nerve come from these cells. The evidence is 

 furnished in the description of Forel and of my own Nissl pre- 

 parations. Forel tofc out the hypoglossal nerve in a new-born 

 guinea pig. The animal was allowed to grow to adult age 

 and was then killed. Regeneration of the peripheral nerve did 

 not take place (as is always the case when the entire nerve is 

 torn out in the new-born). Not only had regeneration not oc- 

 curred; but the neurones which could not regenerate, rt'rgener- 

 atcd completely. Fig. 8, represents the central canal and sur- 

 roundings of the lower part of the medulla oblongata of this 

 animal. On the right side, the large cells described above as 



