NOTES ON THE ANATOMY OF A CYCLOSTOME 

 BRAIN: ICHTHYOMYZON CONCOLOR 



C. JUDSON HERRICK AND JEANNETTE B. OBENCHAIN 



Anatomical Laboratory of the University of Chicago 



TWELVE FIGURES 



In the literature relating to the brain of Petromyzon and its 

 allies there are accounts of the external form of the brain in sev- 

 eral of these species ; but the only full descriptions of the sculp- 

 turing of the ventricular surfaces in correlation with the under- 

 lying internal structures are found in the excellent recent paper 

 by Johnston ('12). A brief reference to some of these structures 

 in the lake lamprey, Ichthyomyzon concolor (Kirtland), was pub- 

 lished by Herrick ('10, p. 470) on the basis of a single series of 

 transverse sections of a specimen 120 mm. long from Lake Erie. 

 Johnston, finding some features of this description out of har- 

 mony with his observations upon other species of petromyzonts, 

 reexamined this series of sections and constructed a plate model 

 of the right half of the forebrain. A figure of the medial view 

 of this model magnified 66 diameters was published in his paper 

 cited above. 



In view of the discrepancies between these two descriptions 

 of the same material, we have undertaken the study of a second 

 specimen of this species. The first specimen was obtained, sec- 

 tioned and loaned to us by Dr. Charles Brookover. The second 

 specimen, also yery kindly put at our disposal by Dr. Brookover, 

 came from the same lot as the first and is somewhat larger, meas- 

 uring 140 mm in length. Both are young adults. The entire 

 head was cut into transverse sections 15 m thick and stained with 

 iron hematoxylin and acid fuchsin. Drawings of the brain were 

 made from these sections with the aid of the Edinger projection 



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THE JOURNAL OF COMPARATIVE NECROLOGY, VOL. 23, NO. 6 



