300 EDWARD PHELPS ALLIS, JR. 
to the chamber of a diverticulum of a plica hyomandibularis 
(Driiner, ’03). 
The conditions in Echidna remain to be considered. In an 
earlier work (Allis, 14 b) I came to the conclusion that the cavum 
epiptericum of Gaupp’s descriptions of embryos of this animal 
was the strict equivalent of the trigemino-facialis chamber of 
Amia less its pars facialis, this conclusion being based on my 
interpretation of Gaupp’s descriptions of the venous vessels of 
the region. According to him (’08, p. 598), there is, in the 
cavum cerebrale cranii of this animal, a large cross-commis- 
sural venous vessel, anterior to the hypophysis and issuing on 
either side through the fenestra pseudo-optica into the cavum 
epiptericum. There, one part of this vessel turns forward and 
passes into the orbit, the other turning posteriorly in the cavum 
epiptericum and becoming the sinus cavernosus. This so- 
called sinus cavernosus is said to pass ventral to the ganglion 
trigeminum, and it is shown, in a figure of a transverse section 
through this region, lying ventrolateral to the base of the taenia 
clino-orbitalis, the hypophysis lying mesial to the taenia. Pos- 
terior to this point, and hence apparently posterior to the sella 
turcica, the sinus cavernosus turns laterally and falls into the 
sinus transversus, the latter sinus descending almost vertically 
in front of the otic capsule. The fusion of these two veins is 
said to form the vena capitis lateralis, which issues from the 
cranial cavity through the hindermost corner of the fenestra 
sphenoparietalis and immediately enters the sulcus facialis on 
the external surface of the chondrocranium. In a slightly older 
embryo the sinus cavernosus is said (l.c., p. 629) still to be 
connected with the sinus transversus, but to be now also pro- 
longed posteriorly as the sinus petrobasilaris, which runs pos- 
teriorly in the cavum cerebrale cranii, sends a branch outward 
through the foramen jugulare, and then itself issues through the 
foramen occipitale magnum. 
From these descriptions I concluded (’14 b) that the so-called 
sinus cavernosus, plus the vena capitis lateralis, must form a vein 
the homologue of the vena jugularis of fishes. That vein could 
not then enter the cavum cerebrale cranii, as Gaupp says it does, 
