ON THE COMMISSURA INFIMA AND ITS NUCLEI IN 

 THE BRAINS OF FISHES. 



BY 



C. JUDSON HERRICK. 



{From the Anatomical Laboratory of the University of Chicago.) 

 With Twelve Figures. 



It has long been known that the brains of fishes possess an 

 extensive mass of fibers which cross the median hne above the 

 ventricle in the region of the nuclei of the dorsal funiculi where 

 the medulla oblongata joins the spinal cord. This is the com- 

 missura infima of Haller. The commissure discovered in a sim- 

 ilar position in the mammals by Cajal (1896, p. 43) was at once 

 recognized by fish neurologists as a homologous structure; and 

 since the commissure of Cajal and its associated nucleus clearly 

 belong to the visceral sensory system (receiving sensory fibers 

 from the visceral roots of the vagus and glossopharyngeus nerves), 

 it has been commonly assumed that in the fishes the commissure 

 is visceral sensory. 



Renewed examination shows that this assumption is correct, 

 but it is not the whole truth. The commissura infima includes two 

 morphologically distinct elements: (i)a visceral sensory commissure, 

 comprising a decussation of vagus root fibers and a commissure 

 of secondary elements from the visceral sensory centers; and (2) a 

 somatic sensory commissure, consisting of secondary fibers from 

 the funicular nuclei and adjacent centers of tactile sensation. Each 

 commissure has associated with it a nucleus. The visceral 

 nucleus was discovered by Cajal and named by him the nucleus 

 commissuralis. The somatic nucleus was first reported in my 

 paper (1906) on the tactile and gustatory centers of fishes, to which 

 the reader is referred for the general topography of this region. 



In the paper last mentioned this commissure of Ameiurus, the 

 common horned pout or cat-fish, was analyzed incidental to the 

 study of the adjacent centers, and found to be very complex. The 



