248 EDWARD PHELPS ALLIS, JR. 
they still persist, an embryo belonging to his third stage and 
said to be 6.6 mm. in length (l. ¢., fig. 8). The lateral edges 
of the anterior prolongations of the parachordals are also not 
affected, as shown in that figure, their mesial edges alone being 
depressed. This depression of the edges must then represent 
a ventral growth of the cartilage, for it is difficult to compre- 
hend how it could have been the result of any pressure of the 
rectus muscles. | 
In Swinnerton’s fourth stage, those parts of the trabeculae 
which border on the fenestra hypophyseos are said to have been 
suppressed, and it is said (/. ¢., p. 518) that: 
In the hinder or parachordal portion, the interparachordal fossa 
has been carried so far away in front of the notochord that the plate 
formed by the median union of the parachordals now furnishes a con- 
siderable portion of the basis cranii. Those parts lying immediately 
on either-side of the fossa have now begun to undergo a movement of 
depression, by which they have already come to he slightly below the 
level of the basis cranu. 
Swinnerton says that this movement of depression is perhaps 
associated with a similar movement on the part of the rectus» 
muscles, but, as just above stated, this ventral growth of the 
parachordal cartilage begins in earlier stages, and it seems im- 
probable that it can there be due to any action of these muscles. 
In later stages of development, it is said (l. c., p. 527) that: 
The process of depression of those parts bounding the interpara- 
chordal fossa laterally has continued, so that this region now appears 
to be a mere downward process of the prootic, with its cartilaginous 
extremity mortised into the sides of the parasphenoid. This appear- 
ance is enhanced by the fact that posteriorly each process is continued 
into a ridge running along the under surface of the hinder portion of 
the prootic. These two ridges are continuous with those already de- 
scribed under the basioccipital, and there is a channel thus formed which 
runs a considerable length of the basis cranii, is closed ventrally by the 
parasphenoid, and opens anteriorly into the cavum cranii by means 
of the interparachordal fossa. 
It is then further said (I. ¢., p. 528) that: 
In the larval Amia this canal is not present, but there is a well- 
marked interparachordal fossa to which the eye muscles bear the same 
