1906.] Observations on the Labyrinth of Certain Animals. 289 



its internal and 5 mm. in its external diameter. The height of the vertex 

 of the canal above the vestibule is 3 - 5 mm. and the diameter of the canal 

 itself at the vertex is 1*25 mm. 



The canals of the Indian gazelle do not diverge from one another at quite 

 such large angles as those of the antelope and the sheep. In this respect 

 they resemble the canals of the pig, though the divergence is still less in the 

 last-mentioned animal. 



The Labyrinth of the Three-toed Sloth (Bradypus tridactylus). 

 (Plate 17, fig. 3.) 



Hitherto the writer has only had the fortune to obtain one example of the 

 edentata, that being the three-toed sloth. To judge from this example, the 

 labyrinth of these peculiar animals will be interesting and instructive to 

 study. 



The cochlea is intermediate in shape between the flattened and the sharp- 

 pointed type, but inclining rather to the former. In this respect the organ 

 differs from the great majority of mammals, since, as has been already 

 pointed out, there is only one other animal among all those which have been 

 examined which does not fall clearly into one of the two types, that animal 

 being the seal. 



The labyrinth measures 10 mm. in extreme length from the outermost 

 point on the posterior canal to the innermost point on the lowest whorl 

 of the cochlea. 



The lowest whorl of the cochlea is 5 - 5 mm. and the second 375 mm. in 

 diameter. The diameter of the tube of the cochlea in front of- the round 

 window is 2 mm. and there is no marked bulging of the floor of the scala 

 tympani in this region. In the latter respect the labyrinth resembles that of 

 man and the monkeys ; but the aqueduct of the cochlea of the sloth is much 

 thicker than in these two orders. There are two and a-half turns in the 

 cochlea and the slant height of the organ, measured from the upper margin 

 of the round window to the apex, is 3 - 75 mm. 



The longest axis of the oval window is rather less than 1*5 mm. in length, 

 and the longest diameter of the vestibule is 3 mm. There are no otoliths of 

 a size sufficient to be recognised by the naked eye. 



The canals of the sloth are quite unlike those of any mammal which the 

 writer has had the opportunity of examining. They are not semicircular in 

 shape, the horizontal canal being the only one that approaches this form, and 

 even it is irregular. The posterior and the superior canals are quadrilateral, 

 or roughly so. The common limb of these two canals arises from each 



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