117 



;--pOC.OCf. 



of the nerve fibres within the brain substances, is shown in Fig. 9, 

 and has been already described. 



Within the furrow and also on the front surface of the brain the 

 new nerve is flattened. It becomes rounded in cross-section as it 

 comes into the angle between the brain-wall and the olfactory lobe, 

 and becomes flattened again on the surface of the lobe. After cros- 

 sing about two-thirds the diameter of the lobe, it enters the fissure 

 between the two divisions of the olfactory, branching unequally as 

 described for other sections. The main trunk of the nerve unites, as 

 in other cases, with 

 the outer bundle of 

 the lateral division 



of the olfactory 

 nerve. There, its 

 fibers mingle with 

 those of the fila ol- 

 factoria and pass 

 between the folds of 

 the nasal membrane. 

 Some of the fibers 

 of the new nerve 

 reach the extreme 

 antcro - lateral por- 

 tion of the olfactory 

 cup, and others ter- 

 minate more cen- 

 trally. 



, The brain of a 

 half-grown Squalus 

 acanthias, about 90 

 cm in length, is re- 

 presented by P'ig. 32. 

 It shows very well 

 the gradations bet- 

 ween the "pup" stage 

 and the adult. In the 

 "pup" stage the ol- 

 factory lobe is well formed, but there is no tractus; in the stage re- 

 presented by Fig. 32, the tractus is forming, and the olfactory nerve 

 proper is being removed from its former position near the brain. The 

 tractus with neurons of the second order form the link between the 



Fig. 32. Dorsal view of the brain of a half-grown 

 Sqalus acanthias (of. with Fig. 1). X about I'/o^ 



