Charles R. Stockard 491 
mouth opening is formed. Here, however, it is seen that the entire por- 
tion or mass of embryonic tissue below the mandibular cleft has in- 
creased considerably in bulk and that the trough-lke furrow still ex- 
tends along the mouth floor in this region. The furrow deepens during 
development and finally cuts or separates the ventral tissue into two 
forward halves, to be described in detail further on. All of this ventral 
mass is the anlage of the so-called “ tongue,” it is seen to be enormous 
and much too far forward for the anlage of such an organ. In all 
respects, however, it corresponds in position and extent to sections of 
the lower jaw portions of most embryos. 
Two of Greil’s, 05, figures which appeared in his paper on the develop- 
ment of the mouth in Triton are shown in outline, Figs. 5 and 6, to 
illustrate the identity of the ventral tissue in my figures with the lower 
jaw tissues. From this identical ventral tissue, as will later be seen, the 
true lower jaw or so-called “ tongue ” develops in a remarkable way. Fig. 
10 shows the mandibular arch greatly curved, but if the embryo at this 
age was flattened dorso-ventrally, as it is at the stage from which Fig. 4 
was made, then Fig. 10 would give the curve of the mandibular arch 
similar to that seen in Fig. 4. 
THE DEVELOPMENT OF THE “ TONGUE” SHOWS IT TO BE THE Homo- 
LOGUE OF THE VERTEBRATE LOWER JAW. 
It may be said that almost nothing is known of the “ tongue ” develop- 
ment in myxinoids. This is strange, since one would think that an 
organ so unique and peculiar as this one is would have been examined by 
the first workers that procured the embryos of these animals. I wonder 
particularly that Kupffer in studying the head development in Bdellos- 
toma did not center his attention upon this organ instead of giving it 
only casual mention. 
Géppert, 02, made in substance the following statement in Hertwig’s 
handbook of embryology, L. 6, p. 36: “The tongue of Petromyzon is 
first attained when the ammocoete metamorphoses, as the complete 
change of life is contemporary with the transformation of the structures. 
The cartilage of the tongue arises according to P. Bujor, g1, in the mas- 
sive connective tissue of the ventral wall of the larval mouth. The 
same author found the tongue muscles evidently first arising from the 
floor of the mouth in the neighborhood of the velum and_ thyroid 
gland. Bujor says that they have nothing to do with the tongue muscles 
of the higher gnathostomes; and they are controlled exclusively by the 
vagus according to Neal, 97, who finds that the so-called ramus recurrens 
