THE MEMBRANOUS LABYRINTH 883 
2. The saccule (Sacculus) is situated in the recessus sphericus of the vestibule. 
From its lower part the ductus reuniens proceeds to open into the ductus cochlearis, 
a little in front of the blind end of the latter. A second narrow tube, the ductus 
endolymphaticus, passes from the posterior part of the saccule, and is joined by the 
ductus utriculo-saccularis; it then traverses the aqueeductus vestibuli, and ter- 
minates under the dura mater on the posterior part of the medial surface of the 
petrous temporal bone in a dilated blind end, the saccus endolymphaticus. 
3. The semicircular ducts (Ductus semicirculares)' correspond in general to 
the osseous canals already described, but it may be noted that while the ampulle of 
the ducts nearly fill those of the osseous canals, the other parts of the ducts only 
occupy about one-fourth of the bony cavities. 
4. The cochlear duct (Ductus cochlearis) is a spiral tube situated within the 
cochlea. It begins by a blind end (Cecum vestibulare) in the cochlear recess of 
the vestibule, and ends by a second blind end (Czecum cupulare), which is attached 
to the cupola of the cochlea. The vestibular part is connected with the saccule 
by the ductus reuniens. The duct is triangular in cross-section, and it is usual to 
regard it as having three walls. The vestibular wall or roof, which separates the 
cochlear duct from the scala vestibuli, is formed by the very delicate membrana 
vestibularis (of Reissner), which extends obliquely from the lamina spiralis ossea 
-6 
Fic. 707.—Lerr Mempranovus LasyrintH (EN- Tic. 708.—ScHeMATIc SECTIONAL Vi=w OF LABYRINTH 
LARGED). (GZENLARG=D). 
1, Cochlea; 2, fenestra vestibuli; 3, fenestra coch- 1, 2, 3, Dorsal, lateral, and ventral ducts; 4, 
3 
lee; 4, ductus endolymphaticus; 5, dorsal, atera 
ventral, duct. (After Ellenberger, in Leisering’s 
las.) 
utricle; 
» sa 6, cochlea; 7, acoustic nerve. 
(After Ellenberge 
in Leisering’s Atlas.) 
to the outer wall of the cochlea. The tympanic wall or floor intervenes between 
the cochlear duct and the scala tympani; it is formed by the periosteum of the mar- 
ginal part of the lamina spiralis and the membrana basilaris, which stretches be- 
tween the free edge of the lamma and the outer wall of the cochlea. The outer 
wall consists of the fibrous lining of the cochlea, which is greatly thickened to form 
the ligamentum spirale cochlee. 
Structure..~—The membranous labyrinth consists in general of an outer thin 
fibrous layer, a middle transparent tunic, and an internal epithelium, composed of 
flattened cells. But in certain situations special and remarkable structures occur, 
among which are the following: (1) The macule acoustice appear as small whitish 
thickenings of the inner walls of the saccule and utricle. The-epithelium here 
consists of two kinds of cells, viz., supporting cells and hair cells. The latter are 
flask-shaped and are surrounded by the fusiform supporting cells. The free end 
of each hair cell bears a stiff, hair-like process composed of a bundle of cilia. Fibers 
of the saccular and utricular branches of the vestibular nerve form arborizations 
about the basal parts of the hair cells. Adherent to the surface of the maculz 
1 Also termed the membranous semicircular canals. 
2 For the finer structure reference is to be made to the histological literature. 
