and the External Characters of the Passerines. 



rings of the bronchi may be moved in both forms; for example, among- the Picarii, iu 

 Trochiliis and Colius, and even in some Tyrannidae. 



On account of Chasmarhi/nckus, the exact separation of these forms of larynx becomes 

 very hazardous, and almost impossible. For although these birds are evidently closely 

 allied to the Ampelinae, and eminently resemble them in the posterior covering of elliptical 

 scales, their larynx pireseuts a combination of the peculiarities of the Singing Birds and of 

 the Picarii ; while, on the one hand, their muscular supply is more developed than it is 

 in the Singing Birds, on the other it is not separated into different muscles, but yet it 

 moves several half-rings ; embraces the first in its whole breadth, the second at its 

 extremities only, and acts on the latter just as do the muscles of the Singing Birds, being 

 distributed to the anterior and posterior ends of the half rings. Chasm arhynclius therefore 

 might be just as well placed among the Singing, as the Shrieking Birds. The question 

 now arises, whether there are other characters in the external structure of the birds, 

 which can serve as a sure sign of internal differences, and which can lead us, on 

 account of their non-variability to understand Nature, where she leaves usn in doubt as to 

 the real bearing of the internal structure. 



A difference, to which Count Keyserling and Professor Blasius first drew attention, in 

 Wiegmann''s Archiv. 1839, I. 332, apj)ears to be of considerable importance in this matter. 

 According to them, the foot of all birds provided with the so-called muscular organ 

 of voice, is clothed posteriorly with a large horny covering — this is the so-called tarsal 

 space (bilaminate planta) — or the foot of these birds is covered on its hinder surface 

 with oblique plates as in the Larks (with which also Maenura would be included, if its 

 larynx can be placed with the vocal larynx, since it has two series of plates on the 

 hinder part of the foot). In birds without the muscular organ of voice, or the Picarii 

 of Nitzsch, the foot according to the same observers, is always without the corresponding 

 horny covering, or even the oblique plates of the Larks, and is covered with scales, 

 reticulated, or naked. 



The importance of this character has been contested by Burmeister, in Wiegm. Archiv. 

 1840, 220, on the ground that in many Singing Birds the posterior parts of the foot 

 are either covered with scales, or granules, or are naked ; as the Ampelidae, Coraeina, 

 Cephalopterus, Chasmarhynclms, Ampelis, Eiori/laimus, Hiipicola, Pipra, Phihalura, Tyrannus, 

 and Psaris. 



Blasius and Keyserling (Id. 1840, 362) do not regard these exceptions as affecting 

 the question, for they do not regard the Ampjelidae as Singing Birds, and see no reason 

 why they should be so; they say that the position of Psaris is doubtful, and that 



