40 



Central Connections. — Having described the course of the 

 nerve, from the median furrow of the prosencephalon to the olfactory cup, 



let us now consider its 

 central connections. In em- 

 bryonic stages the nerve 

 is on the morphological 

 tip of the prosencephalon, 

 on each side, near the 

 neuropore. Fig. 3 shows 

 its position in horizontal 



Fig. 3. Slightly magnified 

 section through the primary fore- 

 brain of a Squalus embryo 20 mm 

 long, showing new nerve and 

 ganglion. Reference lett^-s as in 

 Fig. 1. 



section of the brain of an embryo 20 mm long. This is before the 

 development of the prosencephalon, and the space between the at- 

 tachments of the nerve is elevated. 



Fig. 4 shows its position as seen in transverse sections of the 

 brain of an embryo 37 mm long. 



^<f«• 



n. no*o. 



A 







Fig 4. Two consecutive cross-sections of the brain of a Squalus embryo 37 mm 

 long. From the MiNOT collection, No. 353, sects. 38 and 39. X o^- ^> ^bj. */» in- 

 -poc.olf olfactory cup. n.nov new nerve. 



Fig. 5 shows its attachment to the brain in an embryo 41.5 mm 

 long ^). Owing to unequal growth of the brain-wall , there is now a 



1) Figs. 5, 6 and 7 are taken from specimens in the Minot Collec- 

 tion at the Harvard Medical School. My best thanks are due Dr. Minot 

 for the use of his large collection of sections of Squalus acanthias. 



