HYOMANDIBULA OF THE GNATHOSTOME FISHES 599 
mandibula (Ph) with the hyosuspensorial ligament, and at the 
point where this strand joins the ligament, in intimate relation 
to the ligament, a hitherto undeveloped cartilage appears. This 
second cartilage, called by Krawetz the symplectic, is shown, as 
above described, in his figure 10 b, said to be of a model of an 
embryo of Stage 46/47, the cartilage there lying on the dorso- 
lateral surface of the two strands of ligamentous tissue at their 
point of junction, and in no way imbedded in them. Inaslightly 
older embryo Krawetz shows, in transverse section (1. c., fig. 20), 
what is said to be the same cartilage, but it now lies directly be- 
tween, and hence imbedded in the two ligamentous strands above 
described, at their point of junction. On the other side of the 
head of this specimen the hyomandibula (Ph) is said not to be 
present, and the symplectic, shown in sectional view in Kra- 
wetz’s figures 21 and 22, is said to have here the position of the 
hyomandibula (Hx) of Sewertzoff’s descriptions, but its dorsal 
end has not yet reached the processus oticus palatoquadrati. 
These two so-called symplectic cartilages, so markedly different 
on opposite sides of the head of the same specimen, are quite 
certainly identical, as Krawetz concludes, the cartilage evidently 
undergoing rapid development at about this Stage 47. As one 
of the two is also certainly identical with Sewertzoff’s hyomandi- 
bula they will both be hereafter referred to, as that cartilage is, 
as the cartilage Ex. 
Inaslightly older embryo, Stage 47/48, Krawetz finds hyoman- 
dibular (Ph) and symplectic (Hx) cartilages on both sides of the 
head of the same embryo, and each symplectic cartilage (Hx) now 
reaches the related processus oticus palatoquadrati, exactly as the 
cartilage shown by Sewertzoff does. Krawetz (1. ¢., p. 359) con- 
cludes that the two cartilages Ph and Hx represent the entire 
dorsal half of the hyal arch, and as the cartilage Ph is consid- 
ered by him to represent the hyomandibula the cartilage Ex be- 
comes, doubtless by comparison with the conditions in the Tele- 
ostomi, the symplectic, and is said to represent the hyomandi- 
bula and symplectic combined of Huxley’s desériptions of the 
adult. The antero-lateral end of the hyomandibula (Ph) is 
shown, at this stage, attached by ligament to the internal surface 
