THE OSSICULA AUDITUS AND MAMMALIAN 
ANCESTRY. 
J. S. KINGSLEY AND W. H. RUDDICK. 
THE various students who have investigated the mammalian 
ear-bones have arrived at the most diverse views as to their 
homologies, and it was with the idea of satisfying ourselves 
which of the several accounts of these structures was correct 
that we began our studies. As we progressed, however, it 
became apparent that these ossicles threw no little light upon 
the broader question of the origin of the mammalia. In our 
final paper we will give full details of all of our observations, as 
well as a discussion of the results of other students. The pres- 
ent paper states our views of the homologies of these ossicles 
in a brief manner and shows the bearings which these have 
upon the problem of mammalian descent. The material which 
we have studied has been embryos and larve of Amphiuma, 
Pipa, Ichthyophis, Sceleporus, rat, and pig, and our methods 
have been largely those of wax reconstruction from sections. 
Distinct auditory ossicles occur in no fish-like form, but from 
urodeles to man, in one shape or another, they are present in all 
forms. In urodeles there is a large fenestra ovalis in the outer 
wall of the otic capsule, and in this, connected to its margin 
by membrane, is a cartilaginous plate which is usually called 
the stapes. It is unnecessary for our present purpose to con- 
sider whether this element is formed from the otic capsule, or 
is the homologue of the hyomandibular of the fishes, or, again, 
is an independent structure. In most urodeles this stapes is 
attached to other structures by ligaments alone, but in Amphi- 
uma as well as in Plethodon (¢este Winslow) and in all Czcil- 
ians which have been studied, the stapes articulates directly 
with a stapedial process which is given off from the posterior 
side of the quadrate. At first this quadrate is free from the 
cranium, and is connected only with the slender Meckelian car- 
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