1906.] Observations on the Labyrinth of Certain Animals. 291 



The whole labyrinth measures 8 mm. in length from the outermost point 

 on the vertex of the posterior canal to the innermost point on the lowest 

 whorl of the cochlea. 



The diameter of the lowest whorl of the cochlea is rather less than 4 - 5 mm. 

 in length, while that of the second whorl is only 2*5 mm. in length. There 

 is a marked bulging of the floor of the scala tympani in the region of the 

 round window and the tube of the cochlea at this point measures 2 - 5 mm. in 

 diameter. There are a little more than two and a-half turns in the cochlea 

 and the slant height of the organ from the apex to the upper margin of the 

 round window is 3*75 mm. The general shape of the cochlea is like that of 

 the ungulates and more particularly like that of the pig. The aqueduct of 

 the cochlea is a short tube of about l - 5 mm. in length, this being perhaps 

 the most peculiar feature of the organ in this animal. The aqueduct is 

 thick in proportion to its length and is straight. It is not triangular as in 

 most of the mammalia, but is flattened from above downwards. 



In proportion to the rest of the labyrinth the vestibule is rather large, 

 measuring 4 - mm. in its longest diameter. The longest axis of the oval 

 window is 2'0 mm. in length. There are two otoliths of considerable size 

 in the vestibule. They are larger than those found in any other mammal, 

 with the single exception of the seal, even the porpoise not being an exception 

 in this respect. Both otoliths lie on the inner wall of the cavity, one 

 anteriorly immediately behind the ampullae of the superior and external 

 canals, while the second lies a little below the first. They are both flat, and 

 are of irregular outline. 



The semicircular canals are very like those of other mammals and are 

 beautifully regular in outline, reminding one of the same structures in the 

 antelope, though of course much smaller. The superior canal measures 

 3'5 mm. in its internal, and 5 mm. in its external diameter. The height of 

 the vertex of the canal above the vestibule is 3 mm., and the diameter of 

 the canal itself at the vertex is 0'5 mm. The internal diameter of the 

 posterior canal is 3 mm., and the external diameter of the same canal is 

 4*5 mm. The height of the vertex of the canal above the vestibule is 3 mm. 

 and the diameter of the canal itself at the vertex is 0'5 mm. Thus the 

 posterior canal is smaller than the superior. The smallest of the three canals 

 is the external, which measures 3 mm. in its internal and 4 mm. in its 

 external diameter. The height of the vertex of the canal above the 

 vestibule is 2 - 75 mm., and the diameter of the canal itself at the vertex is 

 - 5 mm. 



There is a very small perilymphatic space in the canals ; it is more notice- 

 able in the angles formed by the ampullae with the canals themselves. In 



z 2 



