ON THE RELATIVE DIMENSIONS OF THE 



OSSEOUS SEMICIRCULAR CANALS 



OF BIRDS. 1 



MAY AGNES HOPKINS. 



The purpose of this paper has been to determine whether there 

 is any relation of the comparative dimensions of the bony semi- 

 circular canals of the ear of birds, either to mode of locomotion, 

 or to genetic affinities. 



These precise questions have apparently not been considered, 

 except in a short paper by Farrar (1831) that was inaccessible 

 to me. Indeed there has been no extended comparative study 

 of the dimensions of these bony canals, though the inner ear 

 labyrinth has been carefully investigated, notably by Retzius 

 (1884). 



In all cases my dissections were made on dried adult skulls. 

 The material used was the collection of the University of Texas. 

 All the American specimens studied had been identified by Prof. 

 Montgomery, and exotic ones by the dealers from whom they 

 were secured. 



The work was done entirely under the direction of Prof. Mont- 

 gomery, to whom lam greatly indebted for his valuable assistance 

 and encouraging sympathy. 



i. MODES OF LOCOMOTION IN BIRDS. 



Archaopteryx, the earliest known bird, was a good flyer if we 

 may judge from its possession of a sternal keel, but it also used 

 its fore-limbs as grasping organs since they were provided with 

 free unguiculate digits. 



What has given birds their superiority over the reptiles was 

 the acquisition of flight, and the main avian peculiarities are refer- 

 able to this mode of locomotion. Birds may have developed 

 flight in one of two ways by saltatory locomotion, whereby 

 the hind limbs were used as propellers, and the fore-limbs as 

 organs of balance ; or by scansorial locomotion on trees, whereby 



Contributions from the Zoological Laboratory of the University of Texas, No. 74. 



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