‘2 3 uae 
ORGANS OF TASTE. 725 
nerve growing out from the neural crest. The vesicle soon becomes pear-shaped ; its 
upper tapering part is named the recessus labyrinthi, and forms the future ductus 
endolymphaticus. About the fifth week, the lower part of the vesicle is prolonged for- 
wards as a tubular elongation, the future ductus cochlearis. This is at first straight, but 
soon becomes curved on itself, so that at the twelfth week all three coils are differentiated. 
From the upper part of the vesicle the semicircular canals are developed and appear as 
hollow disc-like evaginations, the central parts of the two walls of which coalesce and dis- 
appear, leaving only the peripheral rings or canals. The three canals are free about the 
beginning of the second month, and are developed in the following order, viz. : superior, 
posterior, and external. The intermediate part of the otic vesicle represents the vestibule, 
and is divided by a constriction 
into an anterior part, the saccule, 
communicating with the ductus Bi acts 
cochlearis, and a posterior portion, labyrinthi ——____ 
the utricle, receiving the extremities = s- 
of the semicircular canals. Thecon- 
striction extends for some distance 
into the ductus endolymphaticus, 
and thus the utricle and saccule 
are only indirectly connected by a 
Y-shaped tube. Another constric- 
tion makes its appearance between 
the saccule and the ductus coch-  @oentar _ 
learis, near its commencement, and part 
forms the canalis reuniens of 
Superior 
semicircular 
canal 
Posterior 
semicircular 
canal 
External 
semicircular 
canal 
Vestibular —_ fb 
part 
Utricle 
Hensen. The epithelial lining is 
at first columnar, but becomes Saerale 
cubical throughout the whole Coclen x 
labyrinth, except opposite the 
terminations of the auditory nerve, 
where it forms the columnar , ' 
els f th 1; eae A, Left labyrinth of a human embryo of about four weeks; B, 
one SEAN NG IEEE) (as Left labyrinth of a human embryo of about five weeks (from 
utricle and saccule, of the cristeze W. His, jun.). 
ampullze, and of the organ of Corti. 
On the floor of the ductus cochlearis two ridges appear, of which the inner forms the 
limbus laminze spiralis, whilst the cells of the outer become modified to form the rods of 
Corti, the hair cells, and the supporting cells of Deiters and Hensen. 
The mesoderm surrounding the otic vesicle is differentiated into: (1) a fibrous 
layer, the wall of the membranous labyrinth; (2) a cartilaginous external capsule, 
the future petrous bone; and (3) an intervening layer of gelatinous tissue, which is 
ultimately absorbed to form the perilymphatic space between the bony and membranous 
labyrinths. 
Fie. 532. 
ORGANS OF TASTE. 
The peripheral organs of the sense of taste (organon gustus) consist of groups of 
modified epithelial cells, termed the taste buds, which are found on certain parts of 
the tongue and its immediate neighbourhood. 
Taste buds are present in large numbers around the circumference of the 
papillz vallatze, while some are also found on their opposing walls (Fig. 533). They 
are very numerous over the fimbrize linguee, which correspond with the papillee foliate 
of the tongue of the rabbit, and are also found over the posterior part and sides of 
the tongue, either on thé papillee fungiformes or throughout the stratified epithelium. 
They exist, also, on the buccal surface of the soft palate and on the posterior aspect 
of the epiglottis. 
Structure of Taste Buds (Fig. 534)—They are oval or flask-shaped, and 
occupy nests in the stratified epithelium of the regions mentioned. The deep 
extremity of each is somewhat expanded and rests upon the corium; the free end 
is perforated by a minute pore, termed the gustatory pore. They consist of modified 
epithelial cells, which are grouped under the two varieties of—(@) supporting cells, 
and (6) gustatory cells (Fig. 535). The supporting cells are elongated, nucleated 
q 
