186 GENEBAL ORNITHOLOGY. 
several elements which have received special names. In skulls prepared with sufficient care, 
the stapes may he seen m situ, as in fig. 71, st, — an extremely delicate rod, stepped into the 
fenestra ovalis by its foot, the other end protruding freely, and bearing in many cases its 
hammer-like or claw-like stapedial elements. A stapes I have just 
picked out of an eagle's ear is a fourth of an inch long, with a stout 
foot, but a stem as fine as a thread of sewing silk, and at the tympanic 
end a still finer hair-like process half as long as the main stem, from 
which it stands out at a right angle. The ossification is perfect, and 
there appears to have been another similar process which has broken 
off from the cross-like figure shown in fig. 71, st In a raven's skull 
before me the stapes has fallen into the fenestra ovalis, and lies there with 
its head sticking out, though perfectly loose. I cannot withdraw it intact, 
as the expanded foot fits the hole too closely to pass through in any 
position I have succeeded in placing it. It appears to be about as large 
as the eagle's. Close examination at a point somewhere about the fe- 
nestra ovalis, or between that and the eustachian orifice, will discover a 
minute foramen, corresponding to the stylo- mastoid " foramen of mam- 
mals. It transmits cranial nerve 7 (see p. 177), or the facial nerve, which 
has burrowed through the bony acoustic capsule from the brain-cavity 
and entered the tympanic cavity on its way to the surface. There are 
sometimes ttvo such minute foramina, close together, both conducting to 
the brain cavity (neither in common with the internal auditory meatus) ; 
as in the eagle, in which large bird a fine bristle just passes through each. 
Thus in the dry skull of a bird, all the hard parts of the middle ear or 
tympanic cavity, as well as the eustachian tube, can readily be inspected 
from the outside ; even the limits of the opisthotic and prootic bones can be determined to some 
extent, and the ossiculum auditus be seen m situ. There will also be noted, in most birds, the 
articular facet upon the prootic bone for the inner head of the quadrate, as weU as upon the 
squamosal for the outer head of the quadrate ; however these may shift in position, in dif- 
erent birds, they cannot easily be overlooked or mistaken. Details of mere size and configura- 
tion aside, the above general description will apply pretty well to any bird, and should suffice 
for the identification of the objects seen on looking into the ear, though the number and 
variety of the irregular pneumatic openings may be puzzling at first. To see these things 
clearly in a mammaVs ear would require special preparation of the parts, as they lie inside a 
tympanum which is itself at the bottom of a contracted tube. In such an ear, properly laid 
open, would be found a chain of three ossicles crossing the tympanic cavity from the inner 
surface of the tympanic membrane to the opposite surface of the membrane closing the fenestra 
ovalis — the malleus, incus, and stapes, or hammer," anvil " and stirrup ; " and the latter 
would be stirrup-shaped, not trumpet-like with a cross-bar at the mouth-piece. Some mam- 
mals would also show a hyoid bone which would have what are the cerato-hyals of a bird 
produced up toward the ear-parts, and continued to these by a bone called stylo-hyal, or 
styloid process of the temporal"; and any mammal's jaw would articulate directly mth the 
squamosal, — the chain of three ossicles being entirely inside the ear. As to comparing the 
parts now : the mammalian stapes is the stapes or columella of a bird, — its stem and foot at 
least ; the incus of a mammal is represented by one of the claws of the cross-bar of a bird's 
stapes (the sitpra-stapedial element; fig. 83, sst)-, the malleus of a mammal is the great 
quadrate bone of a bird; the stylo-hyal of a mammal is not fairly developed in a bird, unless 
contained in or represented by another claw of the stapes (an m/?'a-stapedial element, ist) ; 
and in these facts is the reason why a bird's lower jaw is articulated indirectly to the skull 
by means of the quadrate, and also why a bird's hyoid bone is not articulated or in any way 
Fig. 83. — Mature 
stapes of fowl, about x 
4 ; after Parker, st, its 
foot, fitting fenestra 
ovalis ; mst, main shaft, 
or medio-stapedial ele- 
ment ; sst, supra-sta- 
pedial ; est, extra-sta- 
pedial ; ist, infra-sta- 
pedial, its end repre- 
senting a rudimentary 
stylo-hyal ; /, a fenestra 
in the extra- stapedial. 
(See st in situ, tig, 71, 
and its embryonic for- 
mation, fig. 67.) 
