The Development of the Alligator 295 
roof is reduced to the usual thin, wrinkled mem- 
brane. Close to the floor of the hindbrain lies the 
notochord (nt), which is large and is distinctly 
vacuolated. To the right of the hindbrain a large 
mass of darkly stained cells (cz) is one of the 
cranial nerves, which is connected with the hind- 
brain a few sections anterior to the one under 
consideration. The pharynx (pf), which is cut 
near its extreme anterior end, is represented by 
three irregular cavities near the base of the fore- 
brain. Scattered throughout the mesoblast, which 
makes up the greater part of the section, are nu- 
merous blood-vessels (5v). 
Figure 15) is twenty sections posterior to Figure 
15a and passes through the tip of the bent-under 
forebrain (fb). On the left the section is anterior 
to the optic vesicle and barely touches the side 
of the optic stalk, which is seen as a small lump on 
the ventro-lateral wall of the brain. On the right 
the connection of the optic vesicle (ov) with the 
forebrain is shown. Dorsal to the optic vesicle 
just mentioned is a markedly thickened and slightly 
invaginated region of the ectoderm (); this is the 
nasal pit; on the left side of the figure the thickening 
is shown, but the section did not pass through the 
invagination. The hindbrain (tb) is somewhat 
narrower than in the preceding figure, but is other- 
wise about the same; the origin of a cranial nerve 
is seen on its left side (cz). The notochord (nt?) 
has the same appearance as 1n the preceding section. 
