38 Oil the Relations between the Structure of the Organ of Voice, 



us in it a marvellous abundance of variations, we may compare it with the sexual parts, 

 as shown in the examination of the Struthious Birds which I laid before the Academy 

 in 1836. 



V. On the Eelations between the Structuee of the Organ of 

 Voice, and the External Characters of the Passerines. 



If we put aside the chief peculiarities of the genera, and review the most ordinary 

 types of the larynx in the Passerines, including the Scansores, or rather the Insessores, 

 we find that there arc three chief forms of vocal organs to be examined : (1) the highly 

 muscular larynx with anterior and posterior muscles, as found in the Songsters, Passeruii 

 Polymyodi (which sing with many muscles); (2) the tracheal organ of voice of the TracheopJioni 

 with one or two lateral muscles ; (3) the larynx of the Picarii with one or several lateral 

 muscles. I do not use the names Polymyodi, TracJieopJioni, Picarii, to distinguish 

 divisions of the Insessores, but only provisionally for forms of the larynx. The essential 

 point of difference between Polymyodi and Picarii is not to be regarded as lying in the 

 different number of muscles which are present, for there are intermediate steps in this, 

 and indeed four or five muscles on either side of the larynx, as in the Singing Birds, 

 or three, as in the Psittacidae, are not very different ; but the characteristic of the larynx, 

 of the Polymyodi is that the influence of their muscles is divided, and is exerted 

 on both the anterior and posterior ends of the moveable rings of the bronchi, while in 

 the Picarii they only act on one part of the ring, the extent of which may vary, and 

 may indeed be over the greater part of the breadth of one ring, as in Tyrannns, Fluvicola, 

 and Pifra. From this point of view the larj'nx of Maenura, although it differs from 

 that of the Songsters in the number of muscles, would be still placed in the general tj'pe 

 of the Polymyodi, in so far as that the muscles act symmetrically on the ends of the 

 half-rings. The larynx of the Picarii is not necessarily limited to one laryngeal muscle, 

 l)ut may possess several, as in the TrochiUnae, and Psittacinae, but they then lie in the 

 same plane, either over or under one another, and are not, as in the Songsters, separated 

 into those on the anterior and those on the posterior face of the larynx. A maximum 

 and minimum is as possible in the larynx of the Picarii, as in that of the Songsters ; 

 a minimum is found in the Maenuritiae, which according to Eyton possess only an 

 anterior and posterior laryngeal muscle, which, however, act on several rings. Several 



