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no reason why this should not be regularly done, for the purpose of 
adding to the specific and generic characters cited. On the whole, the 
ossicles appear to be quite conservative, large groups of rodents having 
them of the same general pattern. Thus, we figure (fig. 1) the malleus 
and incus of Proechimys semispinosus, from Colombia (Leo. E. Miller, 
Am. Mus. Nat. Hist.), which are almost identical in form with those of 
the African Aulacodus. On the other hand, good specific characters 
are not wanting; thus the malleus of Epimys hinder (fig. 2) is easily 
distinguished from that of E. norvegicus. In some cases unexpected af- 
finities seem to be indicated; thus the ossicles of Graphiurus are more 
like those of the squirrels than the true mice. 
The degree of modification or specialisation dif- 
fers greatly, the most extreme form of malleus 
being apparently that of Epirys, a genus probably 
of comparatively recent evolution. 
In the human ear, the end of the stapedial 
process (processus longus) of the incus is about 
Feige Cee on a level with the middle of the manubrium. In 
(Am. M. N.H) Leo E. Paraxerus (fig. 3) and Graphiurus (fig. 4) the 
MillemCell same general relation holds, though the bones 
are very different in detail. In the true mice, however (cf. Dendromus, 
fig. 5; Arviacanthis, fig. 6; Thamnomys, fig. 7) the incus is very short, 
and the stapedial process does not nearly reach the base of the manu- 
brium. This would have the effect of strengthening the vibrations while 
decreasing their amplitude, and would give the animal an advantage 
in hearing notes of high pitch. Thus there appears to be a definite re- 
lation between the size and shape of the ossicles and the voice of the 
animals, although this can at present only be stated in general terms. 
The ossicles, then, exhibit a certain parallelism with recognition marks, 
probably tending to makes the rodents especially sensitive to the voice 
of their species. Perhaps some day an energetic student will collect 
phonographic records of the voices of mammals, and it will be possible 
to determine more exactly how these are related to the structure of the 
ears. It may be also noted that the chirping Orthoptera, much preyed 
on by mice, often have very high pitched “voices”, so much so that they 
are sometimes inaudible to some human beings. It may be advantageous 
to the Orthoptera to be able to call one another in notes so shrill that 
to some animals they are inaudible, but it may also be advantageous 
to the mice to be well fitted for hearing those high sounds. 
The classic work on earbones is that of A. H. G. Doran, in Trans. 
1 We have more recently obtained evidence suggesting that this type is really 
an ancient one. 
