180 TRANSACTIONS OF THE [may 11, 
This is called the horizontal canal. The proximal end is 
in close relation with the proximal end of the anterior 
canal at the recessus utriculus (r. u.); while the distal end 
enters the sinus utriculus through its posterior wall a little 
above the plane of the canal. 
The posterior canal (p.c.) is almost completely separated from 
the body of the ear. At the proximal end just after the canal 
bends inward and forward is an enlargement, the ampulla of the 
posterior canal; from this ampulla, inclosed in a capsular canal 
is a thin membranous tube which connects the ampulla with the 
distal end of the canal. This tube is the connecting tube of 
posterior canal (p.c.t.). It is much larger than the rest of the 
canal and completely fills the capsular canal. 
The only communication which the posterior canal has with 
the body of the ear is a small, short tube, the ductus canalis pos- 
terioris (d.c. p.). It arises from the middle of the connecting 
tube, passes under the distal end of the horizontal canal, and 
enters the sacculus pointing toward the lagena. 
AMPULL. 
The proximal ends of all the canals are swollen into vesicle- 
like bodies having the side farthest from the center flattened at 
the point where the nerve enters. These enlargements are the 
ampulle (a. a., p. a., h. a.). 
The ampulla of the anterior canal is directly above the utricu- 
lus (u.) and opens freely into it. The ampulla of the horizontal 
canal is connected with the utriculus by means of a short tube, 
the ampullar tube (a. t.). It enters the utriculus under the pos- 
terior part of the anterior ampulla. The ampulla of the pos- 
terior canal has been mentioned. It is larger and longer than 
either of the others. 
NERVE SupPtiy. 
The auditory or eighth cranial nerve passes from the brain 
and enters the capsular cavity in the same plane as the lower sur- 
face of the brain and at nearly right angles to the axis of the 
body. Upon entering the capsular cavity the nerve (n.) comes im- 
mediately into contact with the anterior portion of the sacculus 
(s) just under the recessus utriculus (r. u.). At this point the 
nerve divides into two branches. One branch supplies the sac- 
culus, lagena and posterior ampulla; the other the recessus 
utriculus and the ampulle of the anterior and horizontal canals. 
The former branch is made up of two parts: the ramulus pos- 
terioris, that supplies the ampulla of the posterior canal, and 
the ramulus saccularis, which supplies the ventral part of the 
