THE LIMIT BETWEEN ECTODERM AND ENTODERM IN 
THE MOUTH, AND THE ORIGIN OF TASTE BUDS.’ 
I. AMPHIBIANS. 
BY 
J. B. JOHNSTON. 
WitH 21 TExtT FIGURES. 
It has been generally recognized that in man it is not possible to 
locate exactly the limit between ectoderm and entoderm after the 
rupture and disappearance of the pharyngeal membrane. At the same 
time it is clear that the tongue arises from the lower ends of the 
visceral arches and that the floor of the mouth is in the greater part 
lined by entoderm. In the roof the facts are not so clear, but it is 
believed that the stomodzeum is much deeper above than below. Ob- 
viously it can not include the eustachian tube nor the nasal cavity, 
although the latter is of ectodermal origin. How much of the max- 
illary process and the palatal shelf is covered by ectoderm, and how 
much by entoderm, is not known. 
The taste buds are all located in the pharyngeal portion or floor 
of the mouth, with the exception of those in the soft palate. Whether 
the soft palate is covered by ectoderm or entoderm remains to be 
determined. In view of the fact that at least the great majority 
of the taste buds are found in the area which all authors agree is 
lined by entoderm in the embryo, the question may be asked what 
reason, if any, is there for considering that the taste buds are not 
of entodermal origin? The chief reason is the general doctrine that 
nervous structures are of ectodermal origin. The history of that 
doctrine can not be traced here, but it may be said that it does not 
appear to be based upon an exhaustive study of the origin of all 
‘Neurological Studies from the Institute of Anatomy, University of Minne- 
sota, No. 7. 
THH AMERICAN JOURNAL OF ANATOMY.—VOL. 10, No. 1, JAN., 1910. 
