THE EAR. 423 
-situated in the tympanic bulla. On removing the medial wall 
of the bulla, a bony plate is seen separating its cavity into two 
chambers. This plate of bone extends in from the lateral wall 
of the bulla, forming a complete partition except at the dorso- 
caudal part, where a notch in the bone forms a free communi- 
cation between the two chambers. The lateral chamber, or 
tympanum proper, contains the bones of the ear and is limited 
externally by the tympanic membrane. At its cranial end is 
seen the opening of the tuba auditiva, or Eustachian tube. 
The tuba auditiva, or Eustachian tube, is a cartilaginous tube 
about one and a half to two centimeters long, passing from the 
nasopharynx to the middle ear and placing these two cavities 
in communication. The pharyngeal opening is at about the 
middle of the length of the nasopharynx, near the dorsal border 
of the lateral wall; it is a narrow slit two or three millimeters 
long. Thence the tube passes caudolaterad on the ventral 
surface of the sphenoid bone, and enters the tympanic cavity 
through the opening just laterad of the styliform process of the 
tympanic bulla. The tube has a thick, cartilaginous medial 
wall, while the lateral wal] is thin and formed 
of connective tissue. The lumen of the tube 
is a curved slit in cross-section. 
Bones of the Ear (ossicula auditus). —There 
are three small bones in the middle ear, the 
malleus (hammer) (Fig. 171, 1), incus (anvil) 
(Fig. 171, 2), and stapes (stirrup) (Fig. 172). 
The malleus (Fig. 171, 1) consists of a 
Fic. 171.—MALLE- 
US AND INCUS, 
UNITED IN THE 
slender handle (a) with a small neck (4) at- 
tached at an angle to the caudal end of the 
handle. At the end of the neck is a rounded 
head (c) which articulates with the incus (2), 
and together with one part of the incus lies in 
a small fossa dorsad of the fenestra vestibuli. 
From the medial aspect of the neck extends a 
short process of bone (@) to which is attached 
the tendon of the tensor tympani muscle. One 
NATURAL Posi- 
TION. 
I, malleus; 2, in- 
cus. a, handle of 
maiteus; 4, neck; c, 
head; @, process for 
attachment of ten- 
don of M. tensor 
tympani; ¢, wing- 
like plate and pro- 
cess of neck; f, g, 
the two processes of 
the incus. 
side of the neck is produced into a thin wing-like plate, bear- 
ing on its edge a pointed process (¢). 
