STRUCTURE AND CLASSIFICATION OF BIRDS 



pessulus is present. The syrinx of the stork, indeed, and of 

 the American vultures very nearly approaches what we 

 should on a priori grounds regard as the original form of 

 the syrinx. 



In the other direction the syrinx may be further increased 

 in complication ; this is brought about by an hypertrophy of 

 the intrinsic muscles. The simplest case is that of the 

 plover, Vanellus cayennensis, figured and described by 

 Gabrod,' whose figure is here reproduced. It will not need 



Fig. 45. — Sykinx of Vanella cayennensis, fkom in feont (aftee Gaeeod). 



much description ; the principal change is in the enormously 

 thickened pair of muscles. 



This modification of the syrinx, however, is seen at its 

 extreme in certain passerines and in the parrots. Here we 

 meet with a multiplication of the intrinsic muscles, which 

 may exist to the number of three or four pairs. A syrinx of 

 this kind, when found in the Passeres, is frequently termed 

 oscinine, the group of Passeres exhibiting the character being 

 the Oscines, a term, however, which is not now used in the 

 classification of the group. 



' ' On the Trachea of the Tantalus loculatc& and of VaMellus cayennensis,' 

 P. Z. 8. 1878, p. 625. 



