C '*5 ) 
acrofs. The firft Cavity is from the Right to the Left 1 1 Inch, 
and from before to behind i f Inch. The fecond Cavity » Inch 
in length, and f inch at its broadefi: part. The OJficles , wt. the 
Malleolus (a) Incus (E) (/. J are of a proportional big- F/g. n 
nefs, as you fee in the figure, where they are fhewn in their 
true Dimenfions, running from the Malleolus , which touches the 
Membrana Tympani, to the Bafts of the Stapes , which fhuts the 
foramen Ovale (c.) It has but a fmall Cochlea in proportion (dS) Fig. ir. 
whereinto a Branch of the Soft Portion enters-) and another 
Branch of the faid Portion goes into the Cavitas Tympani , whofe 
upper part is covered by the lower fide of the Os Peirofum (b.b.) 
1 was at fome Pains to file down a great part of the Os Petrofum, 
where [ obferv’d how the Hard Portion paft outward from the 
Hole for the Carotid Artery, as is faid, and how the Soft Portion 
after it had entred the Proceffus Petrofus (e.) did divide it r elf in 
to thefe two juft now mention’d Portions, to the Cochlea, and 
Cavitas Tympani. 1 fearch’d for the Labyrinth , or Lined Semilu- 
nares , but could find none ^ by which I concluded, that thefe 
Caverns in the bottom ot the Cavitas Tympani did ferve for the 
fame Ufes in this Animal, as ti e Meanders of the Labyrinth do 
in others-, and that this fecond Cavity did ferve for receiving and 
continuing the Undulations of the Air, for the longer retaining 
of the Sound, as we fee the cavous Apophyjis zJTfafioides does in 
Sheep, Gats, Dogs, &c. and theSpongious one in Men. The Fora- 
men Ovale is but little, and the Bafe of the Stapes very thin and 
(lender (h.) whereby 1 fuppofe the Senfation of Hearing is rather 
perform’d by the Vibrations of the Air upon the Cavitas Tympani , 
than by any afliftance it had from the Cochlea. The upper part 
of the Septa which circumfcrib’d the Caverns in the Cavitas Tym- 
pani, is thicker, and the lower part very (lender ; and I doubt 
not but they communicate with one another by feveral hiatus - , 
whereby what humidity is in the bottom of the Caverns may be 
convey’d from each other, till it come to the Orifice of the A- 
cjHedutt parallel to it, and thereby difeharge it into the Mouth ; 
for the boney part of this Aqucdutt defeends in a (freight Line, 
from the fore part of the bottom of this Cavitas Tympani 5 \ In- 
ches flat, being from the Right to the Left about \ Inch, and from 
before to behind 3 Lines, or 4 of an Inch. I am forry I did not 
know the Os Petrofum would fo eafily feparate for I might have 
obferv’d more narrowly the Structure of the Ear before the 
Scull was boil d ; and ’tis by an accidental Separation of this 
* R Bone, 
