114 THE DEVELOPMENT 



From the relative positions of these two structures, it would 

 ajjpear that the smaller protuberance prevented the actual closure 

 of the internal nares by the larger, there being always a small 

 channel left just at the blunt apex of the latter. In another 

 section, the larger of these two bodies lies so distinctly behind the 

 aperture that it could not have covered it, the blunt tip barely 

 reaching the posterior border of the canal. The granular matter 

 lying near the external opening is distinctly arranged in the tbrm 

 of a number of rods lying closely packed together. 



This, although the largest, is by no means the only invagina- 

 tion in the upper portion of the mouth. Each invagination is 

 connected with a minute protuberance on the surface of the 

 palate by means of delicate canals. From an examination of 

 some of these protuberances and slight invaginations, where the 

 process has apparently only just commenced, it would appear as 

 though the epidermis split into two parts, one becoming invagi- 

 nated and the other raising itself into a slight knob, the latter 

 being decidedly noticeable, whilst there is still scarcely any trace 

 of the former. If these, as I have every reason for believing, be 

 really glandular structures, it would indicate that the external duct 

 is formed rather before the internal gland. 



Immediately behind the pad previously mentioned, there is a 

 raised portion of the epidermis on the lower jaw, looking exactly 

 like a small papilla ; but as it stretches backward to a consider- 

 able extent along the floor of the mouth, I believe this must 

 represent the first formation of the tongue, and especially as no 

 other trace of this organ can be discovered. If I am correct in 

 this suggestion, the tongue also arises from the epidermal layers, 

 not by an invagination, but by the opposite i:)rocess of an 

 outgrowth of the epidermis, the lines producing this outgrowth 

 being most distinctly visible in a section of April ist, which, 

 however, I believe to be somewhat more advanced in develop- 

 ment than the average of that day. The only structure I can 

 make out in this protuberance with a |-inch object-glass is that of 

 almost flattened papillee or slight prominences covering the 

 raised layer. 



In Plate XI., Figs, i to 4, will be found diagrams, in which 

 rough attempts have been made to delineate some of the many 



