MIDBRAIN AND THALAMUS OF NECTURUS 227 



and by the series of cross sections shown in his figures 7 to 18, 

 where the terminology is that of my 1910 paper. In figure 6 

 of McKibben's paper the sulcus s.shab. probably separates 

 two lobules of the habenula and the true sulcus subhabenularis 

 is the one marked s.d. Compare figures 63 and 64 of the pres- 

 ent paper, the cross sections, figures 1 to 14, and page 229 

 beyond. 



Figure 62 illustrates a sagittal section through the brain of 

 Necturus drawn from a series of Weigert sections. The sec- 

 tions were not cut exactly parallel to the sagittal plane, which 

 was reconstructed by superposing camera outlines on tracing 

 paper of all of the sections which pass through this plane. 



On the basis of the sagittal series from which figure 62 was 

 drawn a graphic reconstruction was made to show the relief of 

 the lateral walls of the diencephaUc and mesencephalic ventricles. 

 Camera outlines of the sections were drawn on tracing paper 

 and the locations of the sulci as projected upon the median 

 plane were determined by the superposition of these tracings 

 (fig. 64). Figure 63 illustrates the ventricular sculpturing of 

 this specimen as reconstructed in this way. This graphic re- 

 construction by flat projection was controlled by comparison 

 with figure 5 of McKibben's paper ('11) and with a series of 

 five additional gross sagittal sections which Dr. McKibben 

 made in the spring of 1917 and very kindly placed at my dis- 

 posal. These were prepared according to the directions pub- 

 lished by McKibben ('13, p. 155) which ensure a minimum of 

 distortion. 



Measurements were made from the seven specimens above 

 referred to (six gross specimens and one microscopic), which 

 included, (a) the distance in the median plane from the tuber- 

 culum posterius to the dorso-caudal border of the commissura 

 hippocampi, (b) from the dorsal to the ventral surface of the 

 brain midway between the habenular and posterior commis- 

 sures, and (c) the total length from the cerebellar commissure 

 to the rostral end of the cerebral hemispheres. These measure- 

 ments are given in the accompanying table, in which the 

 measurements a, b, and c are as defined immediately above. 



