116 



lory, the new nerve branches, very irregularly, sending some fibers 

 to the median, but a larger number to the lateral division. This con- 

 dition is not shown in the figure. 



Magnified sections of the brain in different planes are shown in 

 embryos 41.5 mm and 86 mm in Figs. 5, 6 and 7. 



The brain of an embryo about 150 mm long is shown in Fig. 31. 

 This is a stage at which the young are designated "pups" by the fisher- 



poc. olj. 



Vilk/^^- n.olf.l. 

 LoboLf. 



\ oV o\^ 



-V)is''e'Hce- 



Fig. 30. 



Fig. 31. 



a Fig. 30. Brain of embryo of Squalus acanthias 68 mm long. X about 10. 

 Fig. 31. Dorsal view of the brain of Squalus acanthias fn the „pup stage, 

 150 mm long. X about 5. 



men, and is about the size reached in Squalus before being freed 

 from the oviduct of the mother. 



In connection with the development of the hemispheres of the 

 prosencephalon, a median furrow has been formed within which the 

 roots and distal portion of the new nerve have become included. The 

 roots penetrate the brain-wall, and extend backward, terminating in 

 an eminence of the median septum which divides the fore part of the 

 brain cavity into right and left ventricles. The position and course 



I 



