Kappers, Teleostean and Selachian Brain. 85 



it constitutes the frontal continuation and which is situated 

 immediately over and laterally from the central canal. 



Into this communis region there enter without decussation the 

 sensory glossopharyngeus and vagus roots which will be treated 

 here together as they present exactly the same character in fishes. 

 That the vagus gives part of its fibers to the tractus descendens 

 N. V. (Van Gehuchten, C. J. Herrick), I have not been able 

 to confirm. Kingsbury records that it is found in some teleosts 

 and not in others. The greater number of the sensory fibers 

 terminate immediately in that nucleus, thus differing from the 

 higher vertebrates in the fact that there are no descending or 

 ascending tracts such as have been described for the amphibians 

 where the descending sensory ninth and tenth fibers form a bundle 

 of which a part decussates in the com. infima cerebri (Strong 

 and Johnston). 



In his first publication on the oblongata of ganoids Johnston 

 did not mention this decussation of descending ninth and tenth 

 fibers; in his complete description of the brain of Acipenser, how- 

 ever, he describes a decussation of direct root fibers in the com- 

 missura infima, which, moreover, also contains connections of the 

 nucleus connnissurce which is situated immediately under the 

 commissure. In the bonv fishes Mayser described, among 

 others, two sorts of fibers in this commissure: (i) thinner fibers 

 which he thinks are root fibers of the tenth nerve, thus agreeing 

 with Johnston; and (2) thicker fibers which he considers as a 

 secondary commissure of the motor vagus nuclei. Later this 

 region of the teleosts has been examined by Kingsbury and 

 better by C. J. Herrick in Menidia. 



The latter author says of the fasciculus communis behind the 

 lobi vagi that this "is chiefly, if not wholly, composed of secondary 

 fibers from the lobus vagi and not of root fibers." These second- 

 ary fibers participate in the com. infima Halleri, but no root 

 fibers.^ Nor can I see in Kingsbury any mention made of 

 descending root fibers of the vagus which decussate in this com- 

 missure, and the result of my investigations is in perfect accord 

 with theirs. The teleosts differ from the higher vertebrates in 



^In his most recent work on cyprinoids, however, C. J. Herrick mentions root fibers from the 

 sensory vagus to the commissura infima Hallkri and he presumes that similar fibers exist in smaller 

 numbers in other fishes. 



