Johnston, The Brain of Petromyzon. 85 



is impossible to indicate the position of all of the sections accurately in such 

 drawings as Fig. i or Fig. 30. For example, in the brain from which this series 

 of sections was made the fore brain is curved upward much more than in that 

 of Fig. I, so that a line through the optic chiasma and the lower part of the 

 olfactory commissure is parallel with the bundles of Meynert. The drawing* 

 were made at a magnification of 120 diameters and are reduced to 40 diameters. 

 The nerve elements shown are all drawn directly from the sections outlined, 

 except in a few cases where elements are borrowed from corresponding sections 

 of another series in the same plane. No attempt has been made to render the 

 sections diagrammatically complete. 



Fig. J. Through the second sensory spinal nerve. 



Fig. 4 



FH- 5 

 Fig. 6 

 Fig. 7 



Through the first motor spinal nerve. 

 Through the first sensory spinal nerve. 

 Through the hypoglossus. 

 Between XII and the last root of X. 



PLATE II. 



Fig. 8. Through the third root of X. 



Fig. g. Through the sensory IX. On the outer surface of the nucleus 

 funiculi is shown diagrammatically the common plate of cells from which the 

 nucleus trigemini spinalis and the acusticum differentiate. 



Fig. ga. A vertical transverse section through a point between the planes 

 of Figs. 9 and 10. Iron haematoxylin. To show relative position of the sen- 

 sory centers. 



I'ig. 10. Through tne lateral line X nerve and the motor IX. 



Ft^. I J. Through the caudal part of the VII-VllI root complex. 



Fig. II a. Vertical transverse section through the VII-VIII roots. Iron 

 haematoxylin. 



PLATE III. 



Fig. 13. Through the cephalic border of the dorsal lateral line VII root. 

 Fig. /J. Through the V nerve and the tectum. 



Ftg. i^. Through the tectum in front of the dorsal decussation, and 

 through the decussation of the bundles of Meyni'.k 1. 



PLATE IV. 



Fig. /J. Through the posterior commissure and the decussation of the 

 bundles of Meynert. 



Fig. 16. Through the ganglia habenulae and the bundles of Meynert. 

 Fig. //. Through the superior commissure and the corpus manunillare. 



PLATE V. 



Fi^. ij a. Two vertical transverse sections between the planes of Figs. 17 

 and 18 to show the arrangement of the tractus thalamo-episti iaticus, tractus 

 lobo-bull)aris, tractus olfacto-habenularis, etc. lion haematoxylin. The right 

 half of the drawing represents a section rostral to that shown in the left half. 

 The tractus thalamo-epistriaticus is continued ventrally in Fig. 18, but is not 

 labelled. 



