ADDITIONAL NOTES ON THE CRANIAL NERVES OF 

 PETROMYZONTS.^ 



BY 



J. B. JOHNSTON. 



University of Minnesota. 



With Thirty-one Figures. 



In the year 1897 I prepared by the Golgi method a number of 

 series of sections of the head of Lampetra wilderi. These were 

 used for the study of the brain (1902) and were reviewed in con- 

 nection with the study of the components of the cranial nerves 

 in Petromyzon dorsatus (1905). Owing to the fact that certain 

 fibers are impregnated and others not, the Golgi preparations are 

 not in themselves suitable for a complete study of cranial nerve 

 components and such differences were found between the two 

 species that it was thought best not to incorporate any of the facts 

 from the Lampetra series in the description of the nerves of P. 

 dorsatus. The Golgi preparations were therefore laid aside with 

 the hope that they could be supplemented by new preparations 

 and the cranial nerves thoroughly gone over by this method. The 

 time for making these new preparations now seems more remote 

 than ever and I have decided to publish certain results which are 

 entirely clear from the preparations in hand. The animals used 

 were adults. All were taken on their nests just after spawning. 



The general relations of the cranial nerves may first be reviewed 

 by means of figs, i to 11. These are camera sketches from a 

 series of horizontal sections. The anterior part of the right half 

 of the head is shown, including the first two gill sacs. The figures 

 are not schematized at all except that detail had to be omitted, 

 and in figs. 3 and 8 a little is added from the sections adjacent to 

 those drawn and fig. 11 is a reconstruction from several sections. 

 The left half of this figure represents sections farther ventrad than 

 those drawn on the right. ^ The entire series consists of 109 sections 

 and the section drawn is mdicated beneath each figure. In all 



* Neurological Studies, University of Minnesota, no. 2. 



