276 GENERAL ORNITHOLOGY part ii 



point somewhere about the fenestra ovalis, or between that and the 

 Eustachian orifice, will discover a minnte foramen corresponding 

 to the stylomastoid foramen of mammals. It transmits cranial 

 nerve 7 (see p. 262), 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 

 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 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 in 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 

 difterent birds, they cannot easily be overlooked or mistaken. 

 Details of mere size and configuration 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 vai'iety of the irregular jvieumatlc openings 

 may be puzzling at first. To see these things clearly in a numnmaVs 

 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 memljrane 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 mouthpiece. Some mam- 

 mals would also show a hyoid bone which would have what are 

 the ceratohyals of a bird produced up toward the ear-parts, and 

 continued to these by a bone called stylohyal, or "styloid process of 

 the temporal " ; and any mammal's jaw would articulate directly 

 with 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 S2/-prastapedial element ; Fig. 83, sst) ; the 

 malleus of a mammal is the great quadrate bone of a bird ; the 

 stylohyal of a mammal is not fairly developed in a bird, unless con- 

 tained in or represented by another claw of the stapes (an infra- 

 stapedial element, isf) ; and in these facts is the reason why a bird's 

 lower jaw is articulated indirectly to the skull by means of the 



