294 



Dr. A. A. Gray. 



[Jan. 26, 



The superior canal is much the largest and, roughly speaking, is in the 

 form of an ellipse, with the long axis directed upwards and backwards. 



The superior canal measures 6 mm. internally and 8 mm. externally. The 

 height of the vertex of the canal above the vestibule is 6 mm. and the 

 diameter of the canal itself at the vertex is 1 mm. The posterior canal is 

 next in size to the superior and is also in the form of an ellipse. It 

 measures 4 mm. in its internal diameter and 6*5 mm. externally. The height 

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

 itself at the vertex is 1"5 mm. The common limb of the superior and 

 posterior canals is very much shorter than is the case in any of the 

 mammals. The horizontal canal is the smallest of the three and is elliptical 

 in shape, the major axis being in the antero-posterior plane. It measures 

 3 - 5 mm., in internal and 6 mm. in external diameter. The height of the 

 canal at the vertex from the vestibule is 3 - 25 mm. and the diameter of the 

 canal itself at the vertex is 1"5 mm. 



As is the case in most of the birds there is a communication between the 

 horizontal and superior canals at the point at which they cross, but the 

 opening is very small. The horizontal canal does not project so far back- 

 wards in the crested screamer as in the majority of birds and this gives to 

 these two canals an arrangement similar to that found in the mammals. 



The perilymphatic space is well marked in all the canals. 



The Labyrinth of the Masai Ostrich (Struthio masai). 

 (Plate 18, fig. 6.) 



In so far as the writer's investigations go, no examination has been made 

 of the labyrinth of this division of the order of birds. It is, however, one 

 of the most interesting on account of the fact that these birds are less 

 distantly removed from the reptiles than any others. 



Unfortunately both the labyrinths which the writer obtained were 

 broken, and it is therefore impossible to give a description of the complete 

 organ. The most important parts were not destroyed. 



So far as can be judged from the broken specimens, the whole organ 

 measures about 17 mm. in length. The cochlea is relatively small and only 

 measures 6 "5 mm. in length. It has a stumpy appearance and the backward 

 curve is very well marked. The nerve spreads out fanlike at the tip of the 

 organ and at this point there are several small otoliths arranged in the form 

 of a saddle with the concavity directed outwards. This plurality of the 

 otoliths at the apex of the cochlea is not found in any of the other birds 

 which have been examined, though the single otolith which is so often found 

 here is also saddle-shaped and has the concavity in the same direction. The 



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