638 
Nachdruck verboten. 
The Pseudobranchial and Carotid Arteries in Ceratodus Forsteri. 
By Epwarp PHELPS Axis jr., Menton, France. 
In Greiu’s (1913) recently published work on embryos of Cerat- 
odus, the descriptions of the successive stages in the development of 
the arterial vessels related to the mandibular and hyoidean visceral 
arches differ somewhat from those given in 1905 by KELLIcCoTT, and 
a comparison of the resulting vessels with those found in other fishes 
has led to certain conclusions which, if correct, would seem to be of 
some importance. 
GREIL’s descriptions include embryos from the so-called stage 39 
of SEMON’S descriptions to stage 48. In the oldest of these embryos 
the trabeculae have not yet fused with each other in the pituitary 
region, and there is accordingly still a large fenestra basicranialis 
anterior in the floor of the cranial cavity. The anterior edge of the 
parachordal plate forms the hind edge of the fenestra and must re- 
present the hind wall of the future pituitary fossa. The hypophysis 
is shown lying immediately anterior to the ventral edge of the anterior 
end of the parachordal plate, and between it and the anterior end of 
the plate, in the younger stages figured, lies the anterior commissure 
of the lateral dorsal aortae (aortal roots, GREIL). This commissure, 
in stages 39—41, arises from the lateral dorsal aorta of either side 
between the points where that aorta is joined by the dorsal ends of 
the mandibular and hyoidean aortic arches, as it does in the adult 
selachian. In later stages, the points of origin of the commissure 
shift rapidly forward relatively to the dorsal ends of the mandibular 
aortic arches, and in stage 43 they lie anterior to those arches. 
The commissure retains its original position immediately posterior to 
the hypophysis, but it has now become a commissure between the 
internal carotid arteries instead of between the lateral dorsal aortae. 
In still later stages the commissure aborts, and in stage 48 the con- 
ditions are as follows: 
The mandibular aortic arch of either side joins the lateral dorsal 
aorta on the ventral surface of the chondrocranium posterior to the 
anterior end of the parachordal plate, approximately in the plane of 
the foramen prooticum basicraniale of GreEIL’s descriptions, that fora- 
” 
