254 ANATOMY OF THE RABBIT. 
nerve, and the submaxillary ganglion, associated with the 
lingual nerve. 
13. Examination of the middle ear. 
By breaking away the ventrolateral portion of the tympanic 
bulla and clearing the surface, the structures of the tympanic cavity 
may be studied. They are chiefly those already described in 
connection with the skeleton (p. 147), but the following soft parts 
may be identified. 
(a) The tympanic membrane (membrana tympani) is 
stretched almost vertically across the lower end of the 
external acoustic meatus. 
(b) The tensor tympani is a slender muscle, the origin of which 
forwards from the alisphenoid is concealed. It is inserted 
on the manubrium mallei. 
(c) The stapedius is a minute muscle arising from the periotic 
bone above the cochlear fenestra and inserted on the stapes. 
(d) The chorda tympani is a delicate nerve which crosses the 
tympanic cavity, lying between the long crus of the incus 
and the manubrium mallei. 
The nerve is a continuation of the intermediate nerve, a sensory 
root of the facial, which arises independently of the chief or motor root 
and joins the facial in the facial canal of the periotic bone. Its peri- 
pheral coanections are with the lingual nerve and the submaxillary 
ganglion. 
(e) The internal carotid artery traverses the carotid canal 
of the tympanic bone. By breaking away the posterior 
portion of the bulla, the entrance of the vessel into the 
external carotid foramen may be seen. 
The dissection of the parts of the ear as here outlined includes only the 
external and middle portions together with the associated acoustic nerve and its 
entrance to the periotic bone. The parts of the internal ear (Fig. 81) are not 
readily made out without the use of special methods, though their position may 
be estimated by carefully breaking away the surface of the ventral portion of the 
periotic. They include (1) the bony labyrinth, consisting of a series of con- 
nected spaces lodged in the interior of the petrous bone, and comprising the 
cochlea, vestibulum, and the bony semicircular canals; and (2) the mem- 
branous labyrinth, consisting of a second series of spaces contained within the 
first, and comprising the duct of the cochlea, the sacculus, the utriculus, 
and the semicircular ducts, together with their connections and the endolym- 
phatic duct andsac. The membranous labyrinth contains the sensory portion 
of the ear and its cavity is occupied by a fluid material, the endolymph. The 
wall is separated from that of the bony labyrinth by an extensive perilymphatic 
space also occupied by a fluid material termed the perilymph. 
