714 THE ORGANS OF SENSE. 
short process of the malleus—one to the anterior, the other to the posterior margin 
of the notch of Rivinus. <A recess, the pouch of Prussak, is situated between the — 
membrana flaccida and the neck of the malleus. Communicating behind with the — 
tympanic cavity, this pouch may serve as a reservoir to confine pus or other fluid, 
since its opening into the tympanum is above the level of its fioor, a condition — 
analogous to the opening from the antrum of Highmore into the nasal cavity. The : 
fold of mucous membrane which extends downwards to envelop the chorda tympani 
nerve gives rise to two pouches, one in front of, and the other behind, the handle — 
of the malleus; these are named the anterior and posterior recesses of Troltsch. 
The epithelium which lines the mucous membrane is flattened over the membrana 
tympani, promontory and ossicles, but ciliated and columnar over the greater 
portion of the rest of the cavity. 
Vessels and Nerves of the Tympanic Cavity. Tlie arteries which supply the tympanic 
cavity are: (1) The tympanic artery, a branch of internal maxillary, which reaches the cavity by 
way of the Glaserian fissure. (2) The stylo-mastoid branch of posterior auricular, which passes 
through the stylo-mastoid foramen and aqueduct of Fallopius ; it supplies branches to the mastoid 
antrum and air-cells, to the stapedius muscle, to the floor and inner wall of the tympanic cavity, 
and forms an anastomotic circle, around the membrana tympani, with the tympanic artery. (3) 
The middle meningeal artery sends a branch to the tensor tympani muscle, and, after entering 
the skull, gives off its petrosal artery, which is conducted to the tympanum along the hiatus 
Fallopii ; some twigs from the posterior division of the middle meningeal reach the antrum and 
epitympanie recess through the petro-squamous fissure. (4) The internal carotid artery, in its 
passage through the canal in the temporal bone, gives off one or two tympanic twigs, while (5) a 
branch from the ascending pharyngeal accompanies the nerve of Jacobson. The veins drain their 
contents into the pterygoid plexus, the middle meningeal vein, and superior petrosal sinus. The 
nerves which supply the muscles of the tympanic cavity have already been referred to (p. 718). 
The mucous membrane receives its nerves from the tympanic plexus, which is described on p. 648. 
The chorda tympani branch of the facial nerve passes from behind forwards through the tympamie 
cavity. 
Early condition of Tympanic Cavity.—During the greater part of intrauterine existence 
the tympanic cavity is almost completely filled by a soft, reddish, jelly-like embryonic tissue. 
The narrow, slit-like space is lined by epithelium, which is ciliated over the promontory, but 
squamous elsewhere. Towards the end of foetal life, the gelatinous tissue becomes thinned and 
the cavity correspondingly enlarged. At birth it is filled with fluid which becomes absorbed, 
coincident with the passage of air from the naso-pharynx, through the Eustachian tube. 
TE 
INTERNAL EAR. 
The innermost, and, at the same time, the essential part of the organ of hearing 
is situated in the substance of the petrous-temporal bone, and consists of two sets 
of structures, viz.: (1) a series of cavities hollowed out of the bone and constituting 
the bony labyrinth (labyrinthus osseus): these cavities are continuous with each 
Superior semicircular canal 
Aimpulla of superior 
semicircular canal 
is facialis A 
1 
Reeessus ellipticus 
Crista vestibuli | Superior 
semil- 
circular 
canal 
Canal Recessus sphiericus 
External 
semi- 
circular 
canal 
Cochlea 
Scal: mata 9 7 . 
= Scala tympani Posterior 
enestra rotunda F at a 
stra rotunda | | Lamina spiralis ossea me perm 
. | eater = cirenlar 
Fenestra ovalis | | | Posterior semi- Seala vestibuli | canal 
Ampulla of posterior semi- | | | eireular canal Opening of aqueductus | : : 
0 E : ‘ ening of er 
phe a a a Wraeea eee 7 cochlee | | Opening of crus commune 
Ampulla of external semi- Fenestra rotunda | Opening of aqueductus vestibuli 
circular canal Recessus cochlearis 
External semicircular canal 
Fic. 521.--Lerr Bony LABYRINTH (viewed from Fic. 522.—INTERIOR OF LEFT Bony LABYRINTH A 
the outer aspect). (viewed from outer aspect). 
other, and are named from before backwards the cochlea, vestibule, and semicircular 
canals (Figs. 521, 522); (2) a complex arrangement of membranous channels (Fig. 
524), situated within, but not nearly filling, the bony labyrinth and forming the 
iF 8 ey, S 
