RESPIRATORY SYSTEM 



61 



shortly described. The syrinx is an organ special to birds ; 

 there are no hints of it in any reptile. In reptiles there is 

 no modification at the bifurcation of the bronchi ; the tube 

 simply branches, and there are two sets of cartilaginous 

 rings where there was but one. In birds the case is 

 different, and it may be convenient to commence with what 

 may be regarded as the typical avian syrinx, which has been 

 termed the ' tracheo-bronchial,' since the end of the trachea 

 and the beginning / of the 

 bronchi take a share ,in its 

 formation. It is ' fain Jb term 

 this the typical syrinx, since 

 it is found in the majority of the 

 groups of birds ; it occurs, for 

 instance, in such diverse families 

 as Passerines, Ardeidse, Ballidse, 

 Struthiones, Picariae, &c. The 

 accompanying cuts illustrate 

 this form of syrinx in a number 

 of birds, and from an inspection 

 of them the principal features 

 in the organisation of this form 

 of syrinx may be gathered. 

 At the end of the trachea there 

 is usually a certain amount 

 of modification of the tracheal 

 rings which may be more or '''^^''™'^''^*'*^™'''™^^'('^"'*'^'"'"''^') 

 less marked, and may be in different directions. It is not 

 necessary to particularise here, and we can select fig. 40 

 to illustrate one example of this modification, which consists 

 in a complete fusion of the last few rings of the trachea. 

 The bronchi are formed at first of the short semi-rings, the 

 ■wide interspace being occupied by membrane, the tympani- 

 form membrane, which closes them internally ; the extent 

 of this naembrane varies, and below it the bronchial semi- 

 rings become more closely applied — sometimes, indeed, 

 becoming complete rings. The tympaniform membrane of 

 each bronchus is separated from its fellow by a cartilaginous 



Fig. 



40. — Sykinx of Indicato 

 Enlarged. 



