58 NERVE COMPONENTS OF CONY FISHES. 



commonly regarded as associated with the visceral nerves. 

 Among- these structures is the paracentral nucleus. This 

 is regarded by Onuf and Collins ('98) as a motor splanchnic 

 centre. In the cat it resembles very closely the nucleus 

 to which I have given the same name in the fishes. I am 

 willing to hazard the conjecture from the facts already 

 in hand, that this intermediate zone of the fishes 

 is in the broad view a visceral centre and homolo- 

 gous with the visceral centre of the region of the lateral 

 cornu of the mammals. In the fishes the disproportionate 

 size of these nuclei, as compared with the dorsal and ven- 

 tral cornua, is not surprising, in view of the more import- 

 ant role which visceral nerves play in these animals. The 

 paracentral nucleus of these fishes apparently corresponds 

 to the "median nerve cells" of Kolliker ('96, p. 165). 

 Some of the cells described by Van Gehuchten ('95, pp. 

 118 and 123) in this region of trout embryos probably 

 belong to this nucleus. 



Returning now to the oblongata, the homologies can be 

 fixed here with more certainty. The pre- and post-vagal 

 portions of the fasciculus communis in Menidia obviously 

 represent the fasciculus communis of the Amphibia. It 

 is certain that most of the pre-vagal fibres terminate in 

 the lobus vagi. The diffuse terminal nucleus of the 

 Amphibia (the spinal nucleus) has been compacted and 

 enormously hypertrophied in the fishes, being represented 

 in the lobus vagi (which, however, may contain other 

 structures also) and in some fishes the "lobus trigemini " 

 as well. The scattered cells about the lower part of the 

 spinal portion of the fasciculus communis may represent 

 a part of the original spinal nucleus which has not been 

 absorbed into the lobus vagi. 



The homologies with the mammals seem to be not less 



