56 NERVE COMPONENTS OF BONY FISHES. 



nucleus and the scattered cells which in Menidia lie lat- 

 erally of the canalis centralis and in the neck of the ventral 

 cornu (paracentral nucleus) also extend farther cephalad 

 and form a much more compact nucleus. All of these 

 structures may be seen in a single transection (Fig. 15), 

 which passes through the caudal part of the nucleus am- 

 biguus and the cephalic part of the ventral cornu, while 

 the paracentral nucleus and the lateral recticular area 

 extend a considerable distance farther cephalad. At the 

 level of the first spinal nerve the paracentral nucleus has 

 come to lie a little farther dorsally than in the figure so 

 that, instead of lying ventro-laterally of the central canal, 

 it lies laterally of it; /. e., it occupies the position corre- 

 sponding to that of the nucleus ambiguus of the medulla 

 oblongata, and in this position I have followed it as a well- 

 defined nucleus through nearly the entire length of the 

 spinal cord. There is no break in the continuity of the 

 cellular strand, though in parts of the trunk its cells are 

 more numerous than in other parts. Its cells are through- 

 out of the same large size as at first, while the cells of the 

 dorsal cornu are very small. The latter are embedded in 

 a dense gelatinous stroma, while the cells of the paracen- 

 tral nucleus lie in a loose reticulum, in this again agreeing 

 with Menidia. 



I have described at length these structures of the spinal 

 cord in this connection because they seem to me to be 

 related to the communis system of the oblongata. In the 

 fishes the communis system, as I have defined the term, 

 is obviously concerned very largely with visceral sensa- 

 tions and is very intimately related to the viscero-motor 

 apparatus. 



Morphologically its terminal nuclei are not the most 

 dorsal structures of the oblongata, as sometimes stated. 

 Haller, for example ('96, p. 65), agrees with Goronowitsch 

 in regarding the lobus vagi as the continuation of the dorsal 

 cornu. It ' ' occupies a position in the oblongata (dorso- 



