CANINE INFLAMMATORY MASTOID DISEASE. 
351 
fell defined by the lower turn of the cochlea , and above the 
xnestra ovalis , where terminates the polished system of minute 
evers and sound-transmitters, the ossicles ( malleus, incurs, stapes, 
md os orbiculare), that form a chain across the cavity connecting 
be membrana tympani with the vestibule. Passing through the 
°enestia ovalis to the internal ear, the opening of the cochlea and 
he spiral way appear, and beyond, at the back, the semicircular Ca¬ 
lais. Returning and examining the posterior wall of the tym- 
)anum , an opening is revealed leading backward and upward to 
he chamber over the external meatus, the antrum mastoideum , 
; iid beyond, backward and outward (more downward in man) the 
tries of pneumatic cells or mastoid spaces , oftentimes many in 
lumber, perhaps but few, varying even in individuals of the same 
pecies. In most young creatures, especially the new born human, 
he antrum mastoid alone is found, the inner table of the bone 
>eing in an incomplete state of development, and the sense of 
learing problematical, if not absolutely in abeyance. 
Turning now to the central aspect of the os temp oris, observe 
ipon the inner wall of the mastoid the grove curving round upon 
he posterior portion of the petrous bone, that receives the lateral 
inns. If an old skull is at hand, eroded from long burial, evi- 
lenees of decay will most probably appear in the vicinity of this 
canal, which demonstrate how extremely frail is the osseous par- 
ition separating the antrum mastoideum from the middle lobe of 
;he cerebrum, in spite of a polish that inculcates a deceiving ap- 
! >earance of hardness and solidity. In the undeveloped crania of 
/oung animals this partition is most superficial, not infrequently 
entirely wanting, which accounts for discharges from the ears oc¬ 
curring coincidently with convalescence from maladies having no 
lefinite connection with the auditory apparatus, as scarletina in 
children. Note also, in the groove of the lateral sinus a foramen, 
vhich transmits the mastoid emissary vein from without through 
he external surface of the mastoid, transversing the pneumatic 
spaces on its way to form a junction with the sinus! Again, I 
vould call attention momentarily to the scalp surface of the mas- 
| ;oid, and to the thin delicate structure of the outer table of the 
3one directly over the cells or spaces! 
