DESCRIPTION OF PLATES II <fe llL^Coftiinued. 



Fig. 9. — Anterior part of liind-braiu. 

 Fig. 10. — Hiiid-brain and thickeniug auditory epithelium. 

 Fig. 11.— Transverse section through hind-brain of a forty-seven hours' 

 chick, passing througli seventh nerve. Picric acid three and a half hours. 

 X 90. 



Figs. 12, 13. — Transverse sections through hind-brain of a fifty hours' 

 chick. Picric acid. X 90. 



Fig. 12. — Through auditory pit on left side; seventh nerve on right. 

 Fig. 13.^ — Through glosso-pbaryngeal nerve on left side; auditory pit 

 on right. 

 Fig. 14. — Transverse section through hind-brain and roots of seventh 

 nerve of a sixty-seven hours' chick. Picric acid. X 90. 



Figs. 15, 16. — Transverse sections through hind-brain of a ninety-lliree 

 hours' chick. Picric acid, x 27. 

 Fio. 15.— Through fifth nerve. 

 Fig. 16. — Through seventh nerve. 

 Figs. 17-20. — Horizontal sections {vide text for exact plane) through 

 head of a ninety-three hours' chick. Picric acid. X 17. 



Fig. 17. — Through olfactory pit, eye, third and ophthalmic nerves ; 



fore- and hind-brains. 

 Fig. 18. — Through olfactory and third nerves, and through constriction 



between mid- and hind-brain. 

 Fig. 19. — Through point of origin of olfactory nerves from fore-brain, 



PLATE III. 



Fig. 20. — Through point of origin of third nerves from mid-brain. 

 Figs. 21,22. — Longitudinal sections through head of a ninety-six hours' 

 chick. Picric acid, x 15. 



Fig. 21. — Through fifth, seventh, and auditory nerves. In the section 

 from whicli the drawing was made the auditory nerve and vesicle were 

 not so well shown ; they were accordingly filled in from the next 

 section. 

 Fig. 22. — Through olfactory pit ; third, ninth, and tenth nerves. 

 Fig. 23. — Longitudinal section through hind-brain and visceral arches of 

 a 100 hours' chick. Picric acid, x 17. Showing fifth, seventh, eighth, 

 ninth, and tenth nerves, and five visceral arches. 



Fig. 24. — Longitudinal section through the posterior part of the head 

 and the neck of a ninety-six hours' chick. Picric acid, x 15. Showing 

 ninth and tenth nerves, with commissure and spinal ganglia and nerves. 



Fig. 25. — Longitudinal section througli posterior part of head and an- 

 terior part of neck of a 122 hours' chick. Picric acid. X 19. Showing 

 investing mass, infundibulum, mouth with pituitary diverticulum ; sixtii 

 nerve, commissure, and spinal nerves and ganglia. 



Fig. 26. — Longitudinal section through head of a 122 hours' chick. 

 Picric acid. X 17. Showing second, third, fifth, eighth, nintii, and tenth 

 nerves ; with some of the eye muscles, the mouth, and pituitary diverti- 

 culum. 



Fig. 27. — Horizontal section through the first five protovertebrae of a 

 ninety-three hours' chick. Picric acid. X 40. Showing spinal ganglia 

 and connecting commissure. 



Fig. 28. — Horizontal section through fifth, sixth, and seventh proto- 

 vertebrse of a ninety-three hours' chick. Picric acid, x 60. Shows 

 muscle-plates, spinal ganglia, and commissure. 



