308 EDWARD PHELPS ALLIS, JR. 
then there representing the cartilago acrochordalis, and the crista 
transversa representing the anterior end of the parachordal 
plate. 
Sonies calls attention (’07, p. 406) to the unusual position 
of the fenestra basicranialis posterior in Talpa, and suggests 
that the posterior pair of insulae polares correspond to the car- 
tilago acrochordalis of his own descriptions of the chick and duck. 
Terry (’17) says that this fenestra lies, in embryos of the cat, 
between the anterior end of the parachordal plate and the 
cartilago polaris (hypophyseal cartilage), thus agreeing with 
Noordenbos in his identification of it, and he says that it lies 
‘not within the basal (parachordal) plate, but anterior to it, 
as Noordenbos insists.”’ In his figure of a median vertical 
section of a 12-mm. embryo (l. c., fig. 17) he, however, shows 
it lying definitely beneath the turned up anterior end of the 
parachordal plate, in exactly the position I have assigned to it. 
Polar cartilages, lying between the trabeculae and parachor- 
dals, have thus been identified in Acanthias and Lepisdosteus 
among fishes, and in several of the Sauropsida and Mammalia, 
and it is probable that they form an integral element of the 
cranium in all of the Gnathostomata, though probably not 
always developed as wholly independent cartilages. The two 
cartilages embrace the ectodermal stalk of the hypophysis, the 
openang between them thus being the fenestra hypophyseos proper- 
ly so-called, but this fenestra is continued both anteriorly and pos- 
teriorly, at certain stages of development, in most of the Gna- 
thostomata. The anterior prolongation of it les between the 
hind ends of the trabeculae, and although it is generally con- 
sidered to persist, in the Teleostei and Holostei, as part of the 
fenestra ventralis myodomus of the adult, it is probable that 
it becomes largely, if not entirely, suppressed by fusion of the 
trabeculae. The posterior prolongation of it lies, in fishes, 
between the ventral edges of the ventral processes of the prootics, 
and, in the Aves and Mammalia, between the corresponding 
edges of the infrapolar processes. These processes must then 
be homologous structures, and if the ventral processes of the 
prootics of fishes are ventrolateral processes, as I conclude, 
