256 ALICE JOHNSON AND LILIAN SHELDON. 



Fig. 16. — Transverse section through the head end of an embryo at a stage 

 shortly after the closure of the medullary canal, to show the neural ridge in 

 the brain. Owing to the cranial flexure, all three divisions of the brain are 

 cut through. 



Fig. 17. — Transverse section through an embryo slightly older than that 

 from which Fig. 16 was taken, showing the origin of the 3rd nerve as a paired 

 outgrowth from the neural ridge in the mid-brain. 



Fig. 18. — Transverse section through tlie same embryo as that from which 

 Fig. 17 was taken, showing the origin of the 5th nerve from the neural ridge 

 in the hind-brain. The lateral thickening of epiblast on each side is 

 shown. 



Fig. 19.— Transverse section through the hind-brain, to show the origin of 

 the 7th nerve as a paired lateral outgrowth of the neural ridge. The lateral 

 thickening of epiblast, which will give rise to the ear and sense-organ of the 

 7th nerve, is shown on each side. 



Fig. 20. — Transverse section through a somewhat older embryo, showing 

 that the root of the 3rd nerve has shifted to the sides of the mid-brain. 



Fig. 21. — Transverse section, showing the attachment of the Gasserian 

 ganglion to the epiblastic thickening forming the sense-organ corresponding 

 to the 5th nerve. 



Fig. 22. — Slightly oblique transverse section, to show the shifting of the 

 root of the 5th nerve; its attachment is seen to extend continuously from 

 the summit of the brain to a point some way down its side. 



Fig. 23. — Transverse section through an older embryo, to show the shifting 

 of the root of the 5th nerve. The nerve is now connected only with a small 

 area of the side-wall of the brain. 



Fig. 24. — Transverse section through a still older embryo, showing on the 

 right side the superior maxillary and dorsal branches of the 5th nerve grow- 

 ing out from the Gasserian ganglion. On the left the Gasserian ganglion and 

 inferior maxillary are shown. 



Fig. 25. — Transverse section through a young embryo, showing on the left 

 the root of the facio-auditory nerve and its fusion with the epiblast ; on the 

 right the auditory epithelium and ventral continuation of the nerve. 



Fig. 26. — Transverse section through the same embryo as that from which 

 Fig. 24 was taken, but slightly posterior to it. It shows on the right the 

 Gasserian ganglion and inferior maxillary branch of the 5th nerve ; on the 

 left the root, ganglion, and pree-branchial branch of the 7th nerve. 



Fig. 27. — Transverse section through a young embryo, showing the root of 

 the 9th nerve and its fusion with the lateral thickening of epiblast correspond- 

 ing to it. On the right the nerve is seen passing on to the 2nd visceral cleft. 



Fig. 28. — Transverse section through a somewhat older embryo. It shows 

 on the right the root, ganglion, and main branch of the 9th nerve, the last 

 fusing with the epiblast of the dorsal wall of the 2ud visceral cleft. On the 

 left only the main branch and its fusion are seen. 



