EESPIllATOKY 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-broi/cJiial,' since the end of the trachea 



and the beginning of the 



bronchi take a share in its 



formation. It is fair to 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, Ardeidae, Eallidae, 



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 



,, -, . ,, . . FIG. 40. SYIIINX OF Indicato , 



of modification of the tracheal ENLARGED. 



rillgS, which may be more O1 1 ". first bronchial semi-rings. (After GAKKOD.) 



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 membrane 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 



