28 Account of Observed Forms of Larynx. 



The sixth hronchial ring is one of the true thin half-rings, and follows the movements of 

 those before it, but the next is separated from it by the external membrana tympamformis. 

 Special vocal bands exist merely as folds of the mucous membrane on the moveable half- 

 rings. The cartllayo arytaenoidea in the memlrana tijmpaniformis is small, with four corners, 

 and is fastened to the third bronchial riug. 



Tt/rannns crudells Sw. (3Iiisc. despofes Licht.) has three perfect rings at the com- 

 mencement of the bronchus. The muscle is attached to the fourth ring, but appears 

 to move the superior rings also ; it is less broad than in the previously mentioned bird. 



Tyranniis ferox Cuv. {Muscicapa ferox Gm.), genus Tp-annula Sw., has only one perfect 

 bronchial ring; the broad muscle is inserted into the next half-ring. The cartilago arytaenoidea 

 in the membrana tympaiuformis is very large, and broader at the end turned away from 

 the division of the trachea ; it projects into a lateral process, which is united to a second 

 small cartilage by a band. The latter lies between the ends of the fourth and fifth 

 bronchial rings. 



In Elaenia brevlrostris v. Tschudi (Wiegm. Archiv. 1844) also there is only one 

 complete bronchial ring. The membrana tympaniformis contains a very considerable cartilago 

 arytaenoidea. The muscle, of the same character as in the Tyranninae, is inserted into the 

 second bronchial ring. The posterior portion of the larynx is without muscle. 



In Elaenia pagana Sund. {Muscicapa pagana Licht., Platyrhynchus paganus Spix.) the 

 muscle, and the cartilago arytaenoidea are similar ; but a complete bronchial ring is wanting. 

 The broad thick muscle is inserted into the second half-ring. 



Machetornis rixosa Gray, which Herr Stannius most kindly gave me, has an unusually 

 thin muscle, but completely agrees in the structure and muscular supply of its larynx 

 with the rest of the Tyrannidae, and true species of Tyrannus. 



In the Peruvian species of PlatyrhyncJim, which could not be exactly named on account 

 of the incomplete supply of its feathers, there are two or three perfect bronchial rings. The 

 muscle, as in Tyrannus and Elaenia, does not touch the hinder portion of the larynx, and 

 is inserted without contracting into the first, slightly moveable, half-ring. 



The genus Eyrocephalns Gould., P. coronatus G. [Muscicapa coronata L. Gm.) diflJers 

 from the foreo-oing Tyranninae. In it the lateral muscles of the trachea turn towards its 

 anterior wall, in the lower part of the trachea, while they terminate in a common 

 point at its end, as in Pachyrhamphus among the Ampelinae. The first of the bronchial 

 rino-s is perfect. The muscles for the movement of the bronchial rings are reduced to a 

 minimum ; a scarcely recognisable remnant of muscle goes from the last tracheal, to the 

 anterior edge of the second bronchial, ring. The cartilago arytaenoidea is present. 



