286 



Dr. A. A. Gray. 



[Jan. 26, 



in animals which have not, as is evidenced by the monkeys on the one hand 

 and by the sloth on the other. It is found in animals which migrate, such 

 as the seal, and is absent in others which also migrate, such as the porpoise. 

 In so far as the function of equilibration is concerned, the space appears to be 

 of no value, for it is found in the climbing monkey, and is absent in the 

 lemurs, which also are nearly all arboreal. In short, the space may apparently 

 be retained or dispensed with according to the necessities of the case. What 

 these necessities are we do not yet know, but it is very probable that if more 

 room is required for the surrounding structures the perilymphatic space of the 

 canals will disappear. 



The otoliths of mammals have hardly in previous times been examined 

 carefully, it being assumed that they are small, a natural assumption from 

 the fact that in the human subject they are of very trivial dimensions. This 

 assumption is in the main correct, but the writer has already discovered two 

 exceptions, the porpoise and the seal, and another falls to be recorded in this 

 paper, the kangaroo. 



The labyrinths which are described in this paper are : the lion, the Indian 

 gazelle, the three-toed sloth, and the kangaroo among mammals ; the crested 

 screamer and the ostrich among the birds. 



The Labyrinth of the Lion (Felis leo). (Plate 16, fig. 1.) 



The membranous labyrinth of the lion differs in hardly any respect from 

 that of other felidae except in the matter of size. The cochlea is of the 

 sharp-pointed type, and measures 9 mm. in diameter in the lowest whorl. 

 The second whorl measures 6 mm. in diameter. The scala tympani shows a 

 marked bulging at its lower extremity just before it reaches the round 

 window. This is a common feature in the carnivora and in some of the other 

 mammals. The slant height of the cochlea from the upper margin of the 

 round window to the apex of the organ is 4 - 5 mm. in length. There are 

 three turns in the spiral of the cochlea, this being a fraction of a turn more 

 than that of the puma, and a quarter of a turn less than that of the dog. 

 The cat, like the lion, has three turns in its cochlea. 



The vestibule measures 5 mm. in its longest diameter, and there are no 

 otoliths in the cavity of a size sufficient to be recognised by the naked eye. 

 The oval window is elliptical in shape, being in this respect like those of the 

 other carnivora, except the seal, in which the aperture is semicircular (if the 

 contradiction in terms may be excused). 



The semicircular canals are very regular in shape, rounded, and without 

 any noticeable irregularities such as are found in some mammals. Each canal 

 lies in one plane, there being no lateral deviations. The superior is the 



