and the External Characters of the Passerines. 41 



8cytalo]}us). Further, from the characters of Prionitis (a bird without any laryngeal 

 muscles), which j)ossesses three series of hinder plates, we may see that the plates are 

 the commencement of the granules. 



In the third category of Insessores, the external characters are of no use to us in 

 the Tracheopliones with the tracheal organ of voice. There is among them Myiothera, 

 a bird with the covering of its foot undivided at the sides. Conopophaga and Tiuactor 

 have indeed no tarsal scutes, but the anterior plates extend back to the inner side of 

 the foot, and leave a space on the external hinder side only ; other Traclieopliones resemble 

 the Larks in having two posterior series of plates, which meet on the hinder edge of the 

 foot : Thamnojihiltis, CJiamaeza, and Scytalojius. Other members of this family resemble the 

 Picarii in the anterior plates, reaching, on each side, to a granulated space : Anahates 

 and Cinclodes. In Si/nallaxis and Bendrocolaptes the anterior series of plates embraces 

 the foot posteriorly, on its inner side, but on the external hinder side there lies a series 

 of small scutes. 



Certhia and Ticlioclroma, also, among the Singing Birds, have a series of plates on 

 the hinder side externally, but the inner side is encased. There are eonsequentl}', 

 among the Singing Birds, more forms of covering for the feet than the two described 

 by Blasius and Keyserling. 



The following practical rules may be deduced from this discussion, which may be 

 useful in classifying birds not yet examined. 



(i) There is no external character, from which, under all circumstances, it is possible 

 to conclude with certainty what is the internal structure of the Passerinae, and chiefly, 

 what is the structure of the organ of voice ; and the characters of the covering of the 

 feet are not, in single eases, to be relied on. 



(2) The granulated or naked character of the dorsal surface of the foot is, so far 

 as is yet known, a sign of the want of several separate anterior and posterior muscles 

 in the muscular organ of voice ; if, that is, the anterior plates extend, without break, from 

 the lateral space to the granular posterior covering, or to the naked tract; whence 

 we may conclude that Pi/roderus, Tijuca, Querula, Gj/mnoderus, Ptilogonys, Vhi/fotoma, 

 Lipaiigus, and Jgriornis in the New World, and Calyptomena and Promerops in the Old 

 World, although their larynges have not yet been examined, most probably do not possess 

 the muscular organ of voice, with many muscles. Promerops clearly belongs to the 

 Upupinae, the rest partly to the Ampelidae, partly to the Tyrannidae. 



(3) Among the birds of the Old World no example is as yet known of the bilaminate 

 tarsus existing without the muscular organ of voice ; and consequently we may with great 



G 



