NOTE ON THE DEVELOPMENT OF AMPHIBIANS. 
303 
forms the wall of the infundibulum. The lower anterior wall 
of the pharyngeal cavity is fused with the epiblast at M., form- 
ing the oral fusion. A wedge-shaped mass of epiblast ( Hph .) 
extends inward between the oral fusion and the wall of the 
infundibulum ; this is the rudiment of the hypophysis. It is 
not necessary to interpret this condition as an ingrowth of 
the epiblast. I am inclined to think that the wedge-like 
shape of the epiblastic mass is due to the pressure of the more 
rapidly growing brain. It is evident from this section that at 
this stage of the development of Amblystoma there is no ap- 
pearance of a stomodaeum or epiblastic mouth-cavity. From 
this time on the rudiment of the lower jaw begins to extend 
forward, and grows beyond the oral fusion and hypophysis 
toward the nasal tip of the head. The epiblast retains its 
connection with the hypoblast, and also for a time with the 
hypophysis ; thus the epiblast posterior to its point of fusion 
with the hypoblast is pressed close against the epiblast anterior 
to the point of fusion. These two united layers of epiblast 
form an apparently solid mass extending from the hypoblast 
to the surface of the head ( M .). This stage is illustrated in the 
nearly median sagittal section, fig. 17 g. The hypophysis 
[Hph.) has broken loose from the in-folded mass of epiblast, 
and still remains adjacent to the posterior wall of the infun- 
dibulum (In.). The point for the ultimate external opening 
of the mouth ( M .) has been moved by the growth of the lower 
jaw, forward to a position anterior to region of the optic 
chiasma ( Ch .). The position of the perfected mouth-opening 
is shown in fig. 18. The condition of the rudiment of the 
mouth, as represented in fig. 17 g, is that which has been 
described by other writers as a solid ingrowth of epiblast or a 
stomodaeum ; but it is evident from the above-described manner 
of development that the term ingrowth leads to a false con- 
ception as to the origin of the part referred to. The primary 
development of the hypophysis, and the growth forward of the 
lower jaw, are fundamentally the same in Amblystoma as I 
found them in the Lizard. 
During the process above described, the parts of the brain 
