438 



J. B. JOHNSTON 



§ ^^^mummrn' 



21 



^xient 



Fig. 21 Opossum (Didelphys virginiana). Dissection of the right hemi- 

 sphere, as in figure 19. The area parolfactoria is relatively much smaller than 

 in the turtle. The sulcus limitans is nearly horizontal in position. 



Fig. 22 Opossum, medial view of the right half of the same brain as shown 

 in figure 21. Description in the text. 



Fig. 23. Striped gopher (Spermophilus tridecemlineatus). Dissection of right 

 hemisphere as in figure 19. The sulcus limitans runs straight forward from the 

 foramen. Note how the fimbria continues directly caudad from the primordium 

 hippocampi. 



