370 
chordal cartilage (he Figs. 3 and 4) extending from the portion nor- 
mally present in epichordal Anura below the first vertebre to that 
which forms the ventral portion of the urostyle. This hypochordal 
band is fairly broad posteriorly and carries a median ridge (ur Figs. 3 
and 4) which in the stage figured already shows signs of caleification. 
This ridge or keel is steepest posteriorly, and the hind end of it marks 
the posterior termination of the ossified part of the urostyle in its 
fully formed condition. The ridge gets shallower anteriorly and loses 
itself in the cartilage band at about the ninth vertebra. In front of 
this the band is rather narrower. It has parallel sides, and is convex 
below and flat on its notochordal surface. At the level of the fourth 
vertebra it becomes appreciably thicker in a vertical direction, but 
gets thinner again farther forward (see Fig. 4). It broadens out ho- 
rizontally at the level of the third vertebra, and attains the full width 
of the notochord beneath the first vertebra (Fig. 3). Here it is fused 
with the right and left halves of the neural arch, which descend to a 
much lower level than those of the succeeding vertebrae and nearly 
meet below the notochord. In earlier stages than that figured, those 
for instance in which the occipital articulation has not yet developed, 
the hypochordal cartilage is continuous with the basicranial cartilage. 
What is the ultimate fate of the ventral cartilage of Xenopus 
I cannot say, since I have no late larve of the genus in which to 
study its subsequent history. I consider it very doubtful, however, 
if it forms any part of the completed vertebrae, except in the case of 
the first one, or perhaps two, vertebra and the urostyle, into the com- 
position of which the hypochordal cartilage enters in the normal epi- 
chordal development. It most probably shares in the absorption ex- 
perienced by the notochord. In a number of epichordal forms, e. g. 
Alytes, Pelobates, a continuous median band is to be seen on 
the ventral surface of the notochord, but this band is not composed 
of cartilage (except in the regions of the first vertebra and the uro- 
style), and it is narrower and less sharply defined than in Xenopus. 
The hypochordal cartilage is certainly not so extensive in Pipa as in 
this latter genus, and Hasse (20, p. 254) observes as the result of 
his examination of Pipa embryos: — “von da an” i. e. the seventh 
vertebra “bis zum Schädel war die Chorda unten von einem Gewebe 
bedeckt, das man kaum als echten Knorpel anzusehen vermag”. 
In Xenopus the first two vertebre are distinct, although the 
zygapophyses are more feebly developed than in succeeding articul- 
ations; but the statements concerning these two vertebra are very 
much at variance. Mayer in his figure of the skeleton of Xenopus 
(27, Taf. 2, Fig. 6) shows the first and second vertebr& as distinct, and 
remarks (p. 33) that there are eight vertebre in Xenopus, but only 
