2 | MEM BRANOUS a bw RENT Hy ree) 
reagents, splits into several finer filaments. The nerve fibres pierce the membrana 
propria and end in arborisations around the deep extremities of the hair cells. A 
collection of small, rhombic crystals of carbonate of lime, termed otoconia, adheres 
to each of the macule. 
The membranous semicircular canals (ductus semicirculares) are elliptical on 
transverse section (Fig. 525) and possess a calibre equal to about one-fourth of that 
of the bony tubes, to the 
ereater circumference of Soe Wall of 
= < X ia ot on < 2 3S: y Ce € 
which they are attached. Ee pony cena) 
The peripheral portion of — upithelinn : lie = 
the ellipse is fixed,to the — jumics WWE (d Bo branous canal. 
periosteal lining of the ribrons — / IN Hin 
bony canal, whilst the SSS WN © Poriontene 
opposite part is free, ex- > 
cept that it 1s connected 
by irregular bands, the lh 
ligamenta labyrinthi can- [yea 
aliculorum, which pass bh a 
through the perilymphatic a 
space to the bony wall. \ 
The membranous canals 
are dilated in the bony 
ampulle and the mem- 
branous ampulle (am- 
pullee membranaceve) are 
distinctly marked off from 
the concave aspect of the i eee Ze 
z ae <-. ee 
canals. 
EKach membranous ck ay Cy i, m2 ; 
Primcannista cof Ghire: Fic. 525.—TRANSVERSE SECTION OF HUMAN SEMICIRCULAR 
Cana GONSIStS O ECE CANAL (Riidinger). 
layers, vlz.: (a) an outer 
fibrous stratum which contains blood-vessels, together with some pigment, and fixes 
the tube to the bony wall; (>) an intermediate, transparent tunica propria, presenting 
a number of papilliform elevations which project towards the lumen. The fibrous 
layer and tunica propria are thinnest along the attached surface of the tube, and 
in this region also the papilliform elevations are absent; (¢) an internal epithelial 
layer, composed of pavement cells. In the ampulle the tunica propria is much 
thickened and projects into the cavity as a transverse elevation, termed the septum 
transversum, which, when seen from above, is somewhat fiddle-shaped ; its most 
prominent part is covered by auditory epithelium forming the crista acustica, at 
each end of which is a half-moon-shaped border of small columnar cells, the planum 
semilunatum. ‘The cells covering the crista acustica consist of supporting cells and 
hair cells, and are similar in their arrangement to those in the macule of the 
utricle and saccule. The hairs of the hair cells are, however, considerably longer, 
and project as far as the middle of the ampullary lumen. In fresh specimens they 
appear to end free, but in hardened preparations are seen to terminate in a soft, 
clear, dome-like structure, the cupola terminalis, which is striated, the strize converg- 
ing towards its concavity. The nerves form arborisations around the bases of the 
hair cells. 
The membranous cochlea (ductus cochlearis or scala media) commences in the 
recessus cochlearis of the vestibule by a blind extremity (cecum vestibulare), close 
to which it receives the ductus reuniens of Hensen (vide p. 718). It forms a 
spirally-arranged canal inside the bony cochlea and ends at the apex of the latter 
in a second blind extremity, the lagena, or cecum cupulare, which is fixed to the 
cupola and partly bounds the helicotrema. As already stated (vide p. 717), the mem- 
brana basilaris extends from the free edge of the lamina spiralis ossea to the outer 
wall of the cochlea. A second, more delicate membrane, the membrane of Reissner, or 
membrana vestibularis, stretches from the thickened periosteum covering the upper 
surface of the lamina spiralis ossea to the outer cochlear wall, some little distance 
Rese 
