AND OF THE MEMBRANOUS LABYRINTH AND AUDITORY NERVE. 
199 
Explanation of the Plates. 
PLATE VIII. 
Fig. 1. An embryo chick at the thirty-first hour of incubation. 
Fig. 2. An embryo chick at the thirty-third hour. 
Fig. 3. An embryo chick at the thirty-sixth hour. The first rudiment of the eye is 
here seen to be visible in the form of a protrusion from the anterior cere- 
bral cell. 
Fig. 4. An embryo chick at the forty-sixth hour. The optic vesicle is seen now very 
distinct, presenting a slight contraction at its connection with the cerebral 
cell from which it arises. 
Fig. 5. The cephalic extremity of a chick at the same period more highly magnified. 
This Plate is intended to represent the cavity which exists both in the cere- 
bral cell and optic vesicle, and the communication between them. 
Fig. 6. The cephalic extremity of an embryo at the fifty-fifth hour viewed from the 
dorsal aspect, principally intended to represent the mode of formation of 
the crystalline lens. 
Fig. 7. The under surface of the eye of a chick at the seventieth hour. This figure 
shows the spherical form of the eyeball, its contracted tubular end, the 
optic nerve, the mode of formation of the lens, and the fissure which exists 
on the under surface of the eye. 
PLATE IX. 
Fig. 8. The cephalic extremity of an embryo chick at the sixty-second hour (lateral 
view). 
Fig. 9. In this Plate the retina is seen overlapping the margin of the lens at the latter 
half of the third day. 
Figs. 10 and 11. The eye of an embryo chick on the fourth day. 
Fig. 12. The eye of an embryo chick on the fifth day. 
Fig. 13. In this Plate the first rudiment of the ear is visible in the form of a small 
vesicular protrusion from the central part of the medulla oblongata (from 
an embryo chick at the fiftieth hour of incubation). 
Fig. 14. An embryo chick at the fifty-sixth hour. The ear-bulb is now seen to be of 
a pyriform shape, and communicating with the cavity from which it arisesi^ 
Fig. 15. The cephalic extremity of an embryo chick at the sixty-fifth hour of incuba- 
tion. The rudimentary vestibule and auditory nerve are now seen fully 
formed. 
Fig. 16. The ear of an embryo chick at the seventy-second hour of incubation. The 
