Herrick, Medulla Oblongata of Fishes. 409 



that of the chief gustatory cells in the vagal lobe of the carp, though 

 it is much less regular. The commissura infima in this region 

 contains many dendrites of these cells. 



Commissural fibers, both medullated and unmedullated, are 

 scattered throughout the substance of this nucleus and these fibers 

 constitute the greater part of the commissura infima Halleri of 

 fishes. The latter commissural complex, however, contains, as 

 we shall soon see, a separate system of somatic sensory fibers in 

 addition to those just described. 



In Ameiurus, then, the commissural nucleus of Cajal receives 

 direct root fibers from the vagus, probably of unspecialized vis- 

 ceral sensation; it also receives secondary tracts from the vagal 

 lobe which may be both visceral and gustatory, and very small 

 secondary tracts from the facial lobe which are quite certainly 

 gustatory. It does not seem to have any somatic sensory connec- 

 tions. Its efferent path is broadly into the formatio reticularis. 



These three centers, the nucleus intermedius facialis, the nu- 

 cleus intermedius vagi and the nucleus commissuralis of Cajal, 

 are clearly important correlation stations for simple reflexes and 

 seem to form a continuous series. The first receives chiefly gusta- 

 tory excitations from the outer skin and a f^r smaller amount of 

 tactile excitation from the same areas; the second receives gusta- 

 tory excitations from the mouth cavity and general visceral stim- 

 uli by way of the vagal lobe; while the third receives direct root 

 fibers of general. visceral type and secondary visceral (and gusta- 

 tory ?) excitations from the vagal lobe and secondary gustatory 

 tracts from the facial lobe, the latter in very small numbers. The 

 main efi^erent conduction path for all of these centers is the same — 

 to the formatio reticularis of the same and the opposite side, chiefly 

 by short unmedullated tracts. Their connections are, therefore, 

 chiefly with the visceral motor nuclei of the oblongata immediately 

 adjacent, viz: the motor nuclei for mastication, deglutition, etc. 



From the lowest of these nuclei, the commissural nucleus of 

 Cajal, an ill defined visceral area extends caudad on each side 

 into the spinal cord. This is chiefly composed of gray substance 

 and in different fishes contains variable proportions of cells, neu- 

 ropil and medullated fibers. It can be distinctly followed for but 

 a short distance down the spinal cord and soon is lost in the cen- 

 tral gray dorso-laterally of the canalis centralis. This region of 

 the spinal cord of mammals is regarded as a visceral center; the 



