320 The Allio^ator 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). It is 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 Qib) the 

 auditory vesicle (c), which is now considerably 

 more advanced than in earlier figures, is seen as a 

 larger, flask-shaped cavity and a smaller, rotmd one. 

 Between the larger cavity and the hindbrain is the 

 root of a cranial nerve {en), 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 {en) 

 is seen. 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), 



