718 THE ORGANS OF SENSE. 7 
cochlea. Moreover, the cavities of the utricle and saccule are indirectly connected, 
and thus all parts of the membranous labyrinth communicate with each other, and 
the contained endolymph is free to move from one portion to another. The vesti- 
ae bule, also, contains the 
Seen Sune al ductus — endolymphaticus 
\ Ampulla of superior @nd the commencement: of 
Ductus \ 
cochlearis~{ * : : ) 
Ductus reuniens—-> = | 
}semicireular canal the ductus cochlearis. 
Ampulla of external 
Duetus. -.- =~ 
endolymphaticus \ 
canal The utricle (utriculus), 
i the larger of the two sacs 
tater ail (Fig. 524), occupies the pos- 
utriculosaccularis — tero-superior portion of the 
ame Tr bony vestibule. Its highest 
part, or recessus utriculi, 
Fic. 524.—DIaAGRAMMATIC REPRESENTATION OF THE DIFFERENT lies in the Seu elhpiicns 
Parts OF THE MEMBRANOUS LABYRINTH. and receives the ampulle of 
the superior and external 
membranous semicircular canals. Its central part receives on its lateral aspect the 
non-ampullated end of the external canal, and is prolonged upwards and backwards 
as the sinus superior, into which the crus commune of the superior and posterior 
canals open. The ampulla of the posterior canal opens into its lower and inner part, 
or sinus inferior. The floor and anterior wall of the recessus utriculi are thickened 
to form the macula acustica utriculi, to which are distributed the utricular fibres 
of the auditory nerve. Whitish in colour, and of an oval or nearly rhombic shape, 
this macula measures 3 mm. in length and 2° mim. in its greatest breadth. 
The saccule (sacculus) occupies the recessus spheericus, in the lower and fore- 
part of the vestibule (Fig. 522). Smaller than the utricle, it is of an oval shape 
and measures 3 mm. in its longest, and about 2 mm. in its shortest diameter. It 
presents anteriorly an oval, whitish thickening, the macula acustica sacculi. This has 
a breadth of about 1°5 muin., and to it are Hearne the saccular fibres of the audi- 
tory nerve. The superior extremity of the saccule is directed upwards and back- 
wards, and forms the sinus utricularis sacculi, which abuts against, but does not fuse 
with, the wall of the utricle. From the lower part of the saccule a short canal, 
the ductus reuniens of Hensen, opens into the ductus cochlearis, a short distance 
in front of its vestibular or blind extremity. A second small channel, the ductus 
endolymphaticus, is continued from the posterior part of the saccule, and, passing 
between the utricle and the inner wall of the vestibule, is jomed by a small canal, 
the ductus utriculosaccularis, which arises from the inner aspect of the utricle. It 
then enters and traverses the aqueductus vestibuli and ends, under the dura mater 
on the posterior surface of the petrous bone, in a blind extremity, termed the saccus 
endolymphaticus ; this, according to Riidinger, is perforated by minute foramina, 
through which the endolymph may pass into the meningeal ly mphaties. 
The vestibule also contains the blind extremity (ceeum vestibulare) of the 
ductus cochlearis, which les immediately below the saccule in the recessus coch- 
learis of Reichert; from here it passes forwards into the spiral tube of the cochlea. 
The walls of the utricle and saccule are composed of connective tissue which 
blends, along their attached surfaces, with the periosteal lining of the vestibule. It 
is modified internally to form a homogeneous membrana propria, which is covered 
by a layer of pavement epithelium and is thickened at the maculz acustice. 
Towards the periphery of the macule the epithelium is cubical, while on them 
if is columnar. 
The structure of the maculee in the utricle and saccule is practically the same ; 
two kinds of cells are found, viz. (~) supporting cells, and (0) hair cells. The sup- 
porting cells are somewhat oer each containing, near its middle, a nucleus. 
Their branched, deep extremities are attached to the membrana propria; their free 
ends lie between the hair cells and form a thin inner limiting cuticle. The hair 
cells are flask-shaped and do not reach the membrana propria, but end in rounded 
extremities which he between the supporting cells. Each contains, at its deepest 
part, a large nucleus, the rest of the cell being granular and pigmented. From the 
tree end of each there projects a stiff hair-like process, which, on the application of 
Ampulla of posterior canal — a 
Saccus endolymphaticus 
