Die Tympanalgegend des Säugetierschädels. 525 
peeuliarities. with confidenee. The tympanie is exceedingly small, 
and is but slightly inflated into an ineonspieuous bulla, the anterior 
third of which is quite flat and narrows forward to a point. There 
is no tubular auditory meatus, the external opening into the bulla 
being a mere hole, but the anterior lip of this opening is drawn out 
into a short process, somewhat as in existing dogs. Behind the bulla 
is a large reniform vacuity or fossa, of which Leidy remarks: „At 
first, it appeared to me as if this fossa had been enclosed with an 
auditory bulla and what I have described as the latter was a pecu- 
liarly modified auditory process‘ ('69, p. 33). Several speeimens 
representing both the White River and John Day species of Daphaenus 
show that the fossa is normal and was either not enclosed. in bone, 
or, what seems less probable, that the bony capsule was so loosely 
attached that it invariably became separated from the skull on fos- 
silization. At the bottom of the fossa (i. e., when the skull is turned 
with its ventral surface upward) is seen the exposed periotie, or 
petrosal, which is only partially overlapped and concealed by the 
tympanic. Such an arrangement is far more primitive than that 
which is found in any other known member of the canine series, 
and is not easy to interpret. A clue to its meaning may, however, 
be found in the mode of development of the bulla in the recent 
Canidae. Here, as is well-known, the structure consists of an anterior 
membranous and posterior cartilaginous portion, which eventually 
ossify and ceoalesce into a single bulla. Reasoning from this analogy, 
we may infer that in Daphaenus the bulla was also composed of 
two portions, but that only the anterior chamber was ossified, the 
posterior one remaining cartilaginous. Communication between the 
two chambers was provided for by the space which separates the 
hinder edge of the anterior chamber from the petrosal. If this 
interpretation be correet, it supplies an interesting confirmation of 
the results derived from the ontogenetie study of the reeent genera. 
At all events, it seems much more probable that we have to do here 
with a primitive rather than a degenerate structure< (SCOTT, 1898°). 
WiınGeE (1895°) bringt Daphaenus denn auch zu seiner Familie der 
Amphictidae (s. S. 512). Scorr schließt jedoch, wie aus obigem Zitat 
hervorgeht, die Möglichkeit nicht aus, daß eine knöcherne Bulla, 
also ein Entotympanieum, vorhanden gewesen ist, in welchem Falle 
die Übereinstimmung mit Paradozurus größer gewesen wäre. 
Bei Oynodietis aus dem Eocän und Oligocän sind beide Teile 
verknöchert und miteinander verwachsen, aber ihre Grenze ist deut- 
