302 COPE. [Vons ik 
border of the stapes, in a shallow cup-like expansion which abuts 
against the cranial wall. The shaft is cylindric. The meso- 
stapedial is a cartilage which is attached to the narrow extremity 
of the interstapedial much as an anther of a flower is attached 
to its filament. The proximal part of this element is shorter 
than the distal, and is connected with the superior part of the 
quadrate by a ligament, the mesostapedial. The distal part is 
deflected at a strong angle to the interstapedial, and is frequently 
somewhat spatulate by reason of an expansion distally. Its ex- 
ternal face is flat and is applied to the internal face of the epi- 
stapedial. The latter is a cartilaginous disk which closes the 
tympanic chamber externally. It fits like a lid on the cartilagi- 
nous annulus tympanicus, which extends beyond it all round. 
The annulus tympanicus is a thin and wide cartilaginous ring 
with a thickened margin, which is not continuous, but is inter- 
rupted at its superior outline. This interruption is occupied by 
the distal end of the interstapedial, and the proximal part of 
the mesostapedial. The distal part of the latter extend verti- 
cally across the median foramen. These structures have been 
described and figured by Parker (l.c.), who has found them to 
be generally similar in all the families of the order. J] have’ 
examined all the principal types, and give figures of them in 
the genera Xenopus, Discoglossus, Stereocyclops, Scaphiopus, 
Buto, Hyla, and Rana (PL. IL, Figs. 7-12; FU ies ay 
The ceratohyal is slender at the point of connection with the 
skull. This is just in front of and external to the cartilaginous 
base of the interstapedial. It is continuous with the cranial wall 
in some species. It is involved, just distal to its origin, in the 
annular igamentum tympani, which forms the posterior wall of 
the tympanic chamber; but it has no structural connection with 
it. 
The development of the Saliential skull has been studied by 
various authors, especially by Dugés, Huxley, and Parker. I 
have examined series of Rana virescens, R. clamata, and R. cates- 
briana for the purpose of determining the homologies of the 
auricular bones of this order, by a study of their development. 
It has been shown that the ceratohyal cartilage is, for the greater 
part of the life of the tadpole, articulated with the quadrate car- 
tilage, first on its inferior, and then later on its posterior face. 
Professor Parker believes that it is a dismemberment of the dis- 
