320 The Alligator and Its Allies 
paraphysis is very large and is directed backward 
instead of forward, as is usually the case among 
the lower vertebrates (if the alligator may be so 
classed). Itis shown in Figure 17a of a preceding 
stage and will be again shown in a sagittal section 
to be described later. The same areas of more 
dense and less dense mesoblast noted in the preced- 
ing figure are seen here. 
Figure 20c, though still in the head region, shows 
several features that were not seen in the preceding 
figures. On the left of the hindbrain (hb) the 
auditory vesicle (0), which is now considerably 
more advanced than in earlier figures, is seen as a 
larger, flask-shaped cavity and a smaller, round one. 
Between the larger cavity and the hindbrain is the 
root of a cranial nerve (cn), apparently the eighth, 
since in another section it comes in close contact 
with the wall of the larger part of the auditory vesi- 
cle just mentioned. On the right side, ventral to 
the hindbrain, another and much larger nerve (cn) 
isseen. Nearly in the center of the figure is seen a 
small, irregular, thick-walled cavity (p); this is the 
pituitary body, and its connection with the roof of 
the pharynx may easily be made out in another 
section. The mesoblast in this region of the sec- 
tions contains numerous large and small blood- 
vessels and exhibits certain denser areas which 
probably represent the beginnings of the cranial 
cartilages. No sign of the forebrain is seen (the 
plane of the section passing in front of that region), 
