472 DAVIDSON BLACK 
Worthington (I.c.) described a continuation upward of the 
anterior horn nucleus almost to the rostral end of the medulla 
and noted the presence of a number of large cells of ‘Mauthner’ 
in the upper part of the nucleus. This is probably homologous 
with the nucleus that Holm observed in Myxine and to which 
he gave the name ‘“‘ganglion centrale nucleus posterior’ (45). 
Worthington states, moreover, that the nucleus ‘‘gives fibers to 
the vagus,’’ while Holm makes it evident that he did not con- 
sider this cell group to be a nucleus of origin for peripheral 
motor fibers. 
I have examined this cell column rostral to the origin of the 
motor spino-occipital roots in Bdellostoma and have indicated 
some of its largest Miller cells in figures 1 to 6. I could not 
discover any evidence of the direct connection of these cells 
with the roots of the vagus series. They do, however, send 
processes into the neighborhood of the viscero-motor column 
and ventro-lateral area of the bulb. 
Thus, in the present connection I cannot consider this cell 
group to be a part of the somatic motor column proper; it is, 
rather, of the nature of a scattered reticular nucleus of special- 
ized coordinative function,’ such as is commonly found near the 
raphé in the caudal part of the medulla in all vertebrates (van 
Hoevell, 44). 
However, this reticular nucleus in Bdellostoma in all proba- 
bility is the specialized representative of the somatic column 
which has lost, or is in process of losing, its peripheral motor 
components but has retained its primitive dorso-mesial position 
and its intercalary coordination elements. This view would be 
supported by the important observations of Bartelmez on the 
nucleus motorius tegmenti in Ameiurus (9) which is apparently 
represented in Bdellostoma by the reticular nucleus under dis- 
cussion. According to this author the nucleus motorius teg- 
menti, together with the nucleus abducentis, constitutes the 
somatic motor column of the bulb. 
4 The terms ‘coordinative’ and ‘correlative’ are used in the present paper in 
the sense defined by Herrick (42, p. 35). 
