186 



GENEBAL OBNITHOLOGT. 



Fig. 83. — Mature 

 stapes of fowl, about X 

 4; after Parker. s«, its 

 foot, fitting fenestra 

 ovalis ; mst, main shaft, 

 or medio-stapedial ele- 

 ment : 88t^ supra-sta- 

 pedial; est^ extra-sta- 

 pedlal ; i3tj inira-sta- 

 pedial, its end repre- 

 senting a rudimentary 

 stylo-liyal ; /, a fenestra 

 in the extra-stapedial. 

 (See St in situ, fig. Tl, 

 and its embryonic for- 

 mation, fig. 67.) 



several elements which have received special names. In skulls prepared vrith sufficient care, 

 the stapes may be seen in 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 clav^-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 sUk, and at the tympanic 

 end a still finer hair-like process half as long as the main stem, fi-om 

 which it stands out at a right angle. The ossification is perfect, and 

 there appears to have been another similar process which has broken 

 oflf from the cross-like figure shovra in fig. 71, st. In a raven's skuU 

 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 ovaMs, 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 Vain-cavity 

 and entered the tympanic cavity on its way to the surface. There are 

 sometimes two 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 skuU 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 audit4s 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 well 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 wUl 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 pnenmaUc 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, imcus, and stapes, or " hammer," " anvil " and " stirrup ; " and the latter 

 would be stirrup-shaped, not trumpet-like vrith 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 vrith 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 «i«pra-stapedial element; fig. 83, ssf); 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 iwjfra-stapedial element, ist) ; 

 and in these facts is the reason why a bird's lower jaw is articulated indirectly to the skuU 

 by means of the quadrate, and also why a bird's hyoid bone is not articulated or in any way 



