292 



Dr. A. A. Gray. 



[Jan. 26, 



this respect therefore, the labyrinth is like that of the ungulates, with the 

 exception of the gazelle. 



The labyrinth of the kangaroo is not of such an ancient type as we might 

 have expected, save in one respect — the presence of large otoliths. It is 

 unfortunate that the writer has only been able to obtain one example of the 

 marsupials, and it may be that in other species of this order a more ancient 

 type of labyrinth may yet be found. In this connection it should be pointed 

 out that the diprotodont class of marsupials is generally considered to be of 

 more recent origin, and this, if true, may account for the fact that the 

 labyrinth of the kangaroo is not of such an ancient type as we might have 

 expected. 



The Labyrinth of Birds. 



It is quite outside the scope of this paper to describe in detail the typical 

 labyrinth of birds. That work has already been done by several writers and 

 n particular by Eetzius, to whose writings the reader is referred. The 

 present purpose is to show the likenesses and differences which exist 

 between the various species. The reader need only be reminded that there 

 are, as in almost all vertebrates, three canals which occupy nearly the same 

 position relative to one another as they do in the mammals. On the whole, 

 perhaps, they vary more in their disposition than do those of the mammals. 

 One feature seems to be peculiar to the labyrinth of the bird : the horizontal 

 canal, instead of terminating almost in the plane of the posterior canal, 

 passes underneath the latter and projects backwards behind the plane in 

 which it lies. The result of this arrangement is that the two canals form 

 a cross of which the limbs are almost at right angles to one another. At the 

 point of crossing there is a channel of communication between the two 

 canals and it has been supposed that this is a constant feature of the 

 labyrinth of the bird. It certainly is a very general condition, but, as will 

 be seen later, it is not absolutely true of all the birds. 



The perilymphatic space of the semicircular canals of the bird is always 

 well marked so far as the present writer's investigations go. This is a 

 notable distinction of the labyrinth of the bird from that of the mammals. 



The shape of the canals in the bird is in general that of an ellipse rather 

 than of a semicircle. The superior canal, however, varies considerably 

 in shape, and no constant types can at present be described. This canal is 

 always the largest, or rather has been found to be so, in all the examples 

 hitherto examined. 



The vestibule is relatively small. It usually contains otoliths of a size 

 easily seen by the naked eye. They are flattened and are of various shapes. 

 The most usual number of otoliths found in the vestibule is two. 



