MYODOME AND TRIGEMINO-FACIALIS CHAMBER 303 
the parachordal of its side. Nothing is said of the relations of 
the eye-muscles, arteries, and veins to these cartilages. 
Sewertzoff (’97, ’99), in his work on embryos of this same fish 
(Acanthias), did not find these cartilages, and he says that the 
alisphenoid, which is van Wijhe’s antotica, is primarily a wholly , 
independent cartilage and hence not an outgrowth of the par- 
achordal. He considers it to be a prechordal structure, and 
says that it is apparently developed in close relations to the eye- 
muscles, the four rectus muscles and the obliquus superior all 
having their insertions on it. The only other fish in which this 
cartilage has been described is, so far as I know, Lepidosteus, 
where it has been described by Veit and has been already re- 
ferred to when considering that fish. The cartilage is there said 
to give insertion to the rectus externus, this cartilage of this fish 
thus apparently corresponding, functionally, to the base of the 
alisphenoid cartilage of Sewertzoff’s descriptions of Acanthias, 
as it does also to the eye stalk of the adult selachian. A polar 
cartilage, although only described in these two fishes, has been 
recognized and described in certain of the Sauropsida and 
Mammalia. 
In 5-mm. chick embryos and 8 to 9-mm. embryos of the duck, | 
Sonies (’07) finds no cartilage as yet developed in the cranial 
region. The notochord is said to extend far up in the plica 
encephali ventralis, and its tip is there bent slightly ventrally 
and is lost in connective tissues behind the hypophysis. In 
slightly older stages, an unpaired cartilage, the cartilago acro- 
chordalis, develops around the anterior end of the notochord, 
the cartilage inclining dorso-anteriorly and the notochord per- 
forating it from its dorsal surface. The parachordals are said 
to then develop, posterior to this acrochordalis cartilage, as a 
simple unpaired median plate, for, although always thickest 
along their lateral edges, they are always continuous with each 
other dorsal to the notochord and, in most instances, also con- 
tinuous ventral to it. These two primarily independent and 
unpaired cartilaginous plates, the acrochordalis and parachor- 
dalis, then become connected with each other, on either side, 
by a short cartilage which is called the cartilago basiotica, these 
