4 Mr. Hunter’s Obfervations on lbs 
From this foramen begins the inner turn of the cochlea, 
which is the largeft, efpecially at its beginning; the other 
begins from the veftibulum. The cochlea is a fpiral canal coiled 
within itfelf, and divided into two by a thin fpiral bony plate, 
which is compleated in the recent fubjedl, and forms two per- 
fect canals. 
In the recent fubjeT, the foramen rotundum is lined with 
the membrane of the tympanum, which terminates in a blind 
end, forming a kind of membrana cochleae. The other open- 
ing, in the recent fubjedt, communicates with the fpiral turn, 
beyond the membranous termination of the foramen rotundum. 
The foramen ovale has a little projection inwards all round, 
on which the ftapes ftands : within this is the veftibulum, 
which is common to the other fpiral turn of the cochleae, and 
the femicircular canals ; this canal of the cochlea pafl'es out 
hrft in a direction contrary to its general courfe, but foon 
makes a turn into the fpiral. It is round, and not merely a 
divifion of the cochlea- into two by a feptum, but has a mem- 
brane of its own, which is attached to the thin bony plate, 
and lines that part of the cochlea in fuch a manner as to re- 
tain its ftrudture when the bone is removed. The cochlea in 
fome compleats one turn and an half ; in others, more. It is 
not a fpiral on a plane, or cylinder, but on a cone. 
I have already obferved, that by looking in at the foramen 
rotundum, we fee two fmall ridges ; the uppermoft is the 
fwell of the canal from the veftibulum juft deferibed ; the 
lower ridge, which is alfo a canal, may be obferved juft to 
pafs along the foramen belonging to this canal, clofe to the 
feptum between the two ; a circumftance, 1 believe, peculiar 
to this tribe. Its beginning is clofe to the veftibulum, but does 
not open from it, and paftes along the firft deferibed fpiral 
6 turn 
