Syrinx of Foivl. 287 



Adult Structure. 



As far iis the adult structure is (■(•nccniecl, tlie description wliich 

 folloAvs ct>rroborates the work of, and gives details additional to 

 those given by Wunderlich (1884, p. 79), who has figured the adult 

 syrinx, and Garrod (1879, p. ."377), who, in discussing the confor- 

 mation of the thoracic extreniity of the trachea in birds, deals briefly 

 with the condition in (rail us hankiva. 



1 . — Ej:tt ni al Aspect . 

 The syrinx or vocal organ of the bird (known previously to 

 Huxley as the lower larynx), is constituted by the modified tracheo- 

 bronchial junction, and in the common fowl both trachea and 

 bronchi are involved in its formation. Each side of the lowej" 

 tracheal exti-emity presents a membraneous appearance. The ven- 

 tral surface is mainly occupied by a triangular-shaped plate, more 

 or less cartilaginous in structure; and a similar but smaller plate 

 is present on the dorsal stirface. The chamber of the syrinx or 

 "tympanum." is seen to be compressed from side to side, but there 

 is a corresponding increase of depth dorso-ventrally. The outer 

 walls of the bronchi are strengthened by semi-rings of cartilage, 

 while the inner Avails are mem))i-aneous, and bands of fibrous tissue 

 termed the bronchidesmus, pass from one bronchus to the other, so 

 as to enclose beneath the bronchial junction a large air space. The 

 body of the ventral triangular plate is seen to be continuous with 

 that of the dorsal surface, through the medium of a semi-carti 

 aginous or calcareous rod, termed the pessulus. The basal angles 

 of the plates articulate with the extremities of the first bronchial 

 semi-rings, and in close relation to each side of the plates are the 

 lower tracheal rings, which are much modified, lying embedded in 

 the thin membraneous walls of the trachea. As to the syrinfreal 

 muscles, they do not appear to be directly and intimately associated 

 with the syringeal membranes, as they are in many other birds. 

 Lastly, the whole of this syring(>al chamber, or "tympanum," is in 

 close relation to respiratory air sacs, whicli extend, not only up 

 between the two bronchi, lint also around each surface of the svrinx, 

 so that the whole organ is completely enveloped. 



II. — Def ailed strurturc of the syrinx. 

 The syrinx consists of the following structures : — 



1. Supporting framewoi-k, 



2. Syringeal mrmbranes, 

 .3. Syringeal muscles. 



4. Svrintrcal air sacs. 



