410 'Journal of Comparative Neurology and Psychology. 



same is probably true for the fishes, though we have no very pre- 

 cise knowledge of the central relations of the visceral components 

 of the spinal nerves in these types. 



Figs. I to 6 illustrate a series of transections through the brain 

 of Ameiurus stained by the method of Weigert-Pal, all drawn 

 to the same scale, extending from the spinal cord as far cephalad 

 as the nucleus intermedins vagi. For the arrangement of the vis- 

 ceral centers cephalad of this point, consult my former paper (Her- 

 RiCK, '05). 



Reviewing now the visceral centers, in the spinal cord of fishes 

 we have not yet clearly demonstrated these centers save at the 

 cephalic end, where we find the central gray dorso-laterally of the 

 canalis centralis related to the cerebral visceral centers. Passing 

 cephalad from this primary visceral zone, we have a series of three 

 visceral sensory centers which seem to have been differentiated 

 successively from the spinal cord cephalad. The commissural 

 nucleus of Cajal differs in no essential respect from the visceral 

 region in the vicinity of Clarke's column and the intermediate zone 

 of the mammalian spinal cord save for the greater crowding and more 

 medial position of its cells. In both cases the dorsal commissure con- 

 tains both root fibers and dendrites of the cells of the nucleus. The 

 condensation of both nucleus and commissure in the oblongata are 

 simply explained on mechanical grounds, as due to the crowding 

 of the commissural elements backward by the opening out of the 

 membranous roof of the fourth ventricle. Another important fac- 

 tor in the condensation of this nucleus is the usurpation by the 

 intestinal, cardiac and oesophageal branches of the vagus of vis- 

 ceral functions which primitively pertained probably to the spinal 

 cord, for this nucleus appears to be the primary end-station for 

 these vagal branches, at least, in part. 



We conclude, therefore, that the commissural nucleus of Cajal 

 and its commissure represent an enlargement of the visceral sen- 

 sory centers of the spinal cord, but present no evidence of great 

 specialization otherwise. 



It is important to bear in mind from the start, that, in addition 

 to the visceral commissural nucleus, or nucleus of Cajal, to which 

 alone we have referred in the preceding pages, there is in this region 

 another unpaired nucleus, which I shall call the somatic commis- 

 sural nucleus. Associated with it is a somatic portion of the com- 

 missura infima. This nucleus has not, so far as I know, been 



