Structure and Relationships of the Labyrinth. 525 
iW i 
et 7 —r (é 
PP : oO vAe oO 
R ad 
a Cc 
goes 
WI 
pope ce ! 
end creer (iat e 
ae 
ama ee 
d 7 
| of foe a ih , 
SCHEME OF THE ARRANGEMENT OF THE DucTus PERILYMPHATICUS, ETC., IN REPTILES, 
Birps, AND MAMMALS. 
ie) 
Fic. I.—Reptile, Monitor.—a., aqueduct of perilymph. c.c., cochlea. y., perilymph recess. 
d., dehiscence on roof of perilymph recess through which the perilymph is in direct 
communication with the cerebro-spinal fluid. This dehiscence becomes drawn out 
into the form of a short tube in the bird anda long tube in the mammal, and in 
these two divisions is termed the aqueduct of the perilymph. 7., round window, 
closed by a membrane, represented by a dotted line. 
¥ic. [J.—Bird, Rhea, etc.—o., oval opening between scala tympani of cochlea and _ peri- 
lymph recess ; it is not closed by a membrane. The other letters correspond with 
those in fig. 1, but it is to be noted that the oval opening, d., in the reptile 
becomes the tube, d., in the bird. The oval opening, o., is present in all birds 
hitherto examined and in at least some reptiles, e.g., alligator. 
Fic. I1J.—Echidna.—The letters correspond with those of figs. I, II, ete. 
Fie. [1V.—Marsupial, Kangaroo.—The letters correspond with those of the other figures. 
Fie. V.—Ungulates, Carnivora, etc.—The letters correspond with those of the other 
figures. 
Fig. V1l.—Primates, including Man.—The letters correspond with those of the other 
figures. 
DESCRIPTION OF PLATES. 
PLATE 19, Fra. 1. 
The Left Membranous Labyrinth of the Monitor, Varanus salvator, viewed from the 
outer aspect. x 5. The organ is rotated slightly counter-clockwise. The superior 
canal, s., is to the left ; the posterior, p., to the right ; and the horizontal, ., is seen 
between them. ‘The horizontal canal has no communication with the posterior canal 
at the point at which they cross. The large oval saccule is seen filling to a great 
extent the space between the canals, and the otolith apparatus, 0.s., occupies a large 
portion of the saccule. The single crystalline otolith of the utricle, 0.u., is seen 
internal to and behind the ampulle of the horizontal and superior canals respec- 
tively. The oval window, /fo., is seen opening into the lower posterior portion of the 
saccule below the arch of the horizontal canal. Immediately to the left of the oval 
