49() J. B. JOHNSTON 



Figs. 6 to 14 Transverse sections through the right hemisphere of the 

 Chelydra embryo illustrated in figures 1 and 2. 



Fig. 6 Section just caudal to the foramen interventriculare. This is the 

 most caudal section in which the nucleus caudatus can be recognized and here 

 it practically fuses with the nucleus of the lateral olfactory tract. Both are 

 undoubtedly parts of the primitive basal olfactory centers which have been car- 

 ried out into the caudal pole of the hemisphere evagination. There is in this 

 section no apparent boundary between these nuclei which enter into the amygda- 

 loid complex and the general pallium. 



Fig. 7 Section through the caudal part of the foramen, 120 microns rostral 

 to figure 6. The nucleus caudatus is much more distinct and the proliferation 

 of cells for the nucleus lentiformis begins to appear. There is now a slight indi- 

 cation of the latera* boundary of the pallium. The letters s.v.m. in this and 

 figure 8 indicate the position in which the middle ventricular sulcus is to be 

 formed, although it is not actually present in these sections. 



Fig. 8 Section through rostral part of the foramen, 100 microns rostral to figure 

 7. The lateral olfactory area is represented chiefly by cell masses adjacent to 

 the diagonal band. The nucleus caudatus begins to be separated from this area 

 by the crus entering the hemisphere. The lentiform proliferation is larger and 

 the clear space just above it, which corresponds to the zona limitans lateralis in 

 lower vertebrates, is present from this level forward. 



Fig. 9 Section through the rostral wall of the foramen. The position of the 

 foramen is represented by the light space at the medio-ventral angle of the 

 ventricle. The crus has now separated the nucleus caudatus from the nucleus 

 of the diagonal band and both are somewhat removed from the larger mass of 

 the lateral olfactory area which is here labeled l.pyr. The middle ventricular 

 sulcus which is present in this section extends farther caudally in order embryos 

 and adult. 



