SVRINX 941 
inner tympaniform membrane may also be present. In typical 
cases the Trachea has no sounding membranes, and to such belong 
Steatornis, various Caprimulgi and Cuculi—notably Batrachostomus, 
Podargus, Crotophaga, Piaya and Guira ; but there are other members 
of these groups, as Agotheles, Nyctidromus, Cuculus and Centropus, 
in addition to certain Striges, as Asio accipitrinus, which shew stages 
intermediate between the typical Bronchial and Tracheo-bronchial 
Syrinx, in so far as the lower part of the Trachea has incomplete 
rings only, with no pessulus, and is, as in Centropus, split into a right 
and left half, so that it assumes the Bronchial character. 
III. Syrina tracheo-bronchialis, which may be regarded as the 
normal form, the other two being modifications of it, yet it is 
Raven. LaTeraL AND DorsaL VIEW OF SYRINX. 
Bur. mt. rv. second, third and fourth bronchial rings ; Nos. 7-7, as on page 940. 
difficult to give such a diagnosis of it as will apply to all its modi- 
fications. The essential feature is that the proximal end of the 
inner tympaniform membrane is attached to the last pair of tracheal 
rings. In the Oscines the four or five distal tracheal rings are solidly 
fused into a little box which communicates with the Bronchi; the 
first and second bronchial semirings are closely attached to the 
Trachea; and the spaces between the second and third and third 
and fourth semirings are generally closed by outer tympaniform 
membranes. Similar arrangements exist in many other birds ; but 
the chief outer membrane is frequently formed between the last 
tracheal and the first bronchial ring, as in Rhea, Anseres, Sphenisct, 
Perdix, Cypselus, Aluco flammeus and Rupicola. Most peculiar 
features are shewn by Gallus and the Psittaci; but in fact the 
modifications are very numerous, as may well be expected from the 
