458 STRUCTURE AND CLASSIFICATION OF BIRDS 



The aftershaft is always small, and sometimes absent. 



In the 2)terylosis (according to NITZSCH) the pectoral tract 



divides about halfway down the 

 neck ; it is broad, and gives off on 

 each side a stronger outer band. 

 The dorsal tract also divides 

 about halfway down the neck, and 

 encloses a long narrow space. 



The number of rectrices in 

 various genera is shown in the 

 annexed table. 



Rectrices 



Bizinra lobata . . . .24 



Anas specularis . . . .14 



Aims boschas . . . . .14 



Aix sponsa ... .16 



Erismatitra rnbida . . . .18 



Cereopsis Novce Hollandics . . 14 ' 



Plectropterus gambcnsis . . .16 



Cygnus musicus . . . .24 



Fuligula rufina . . . .16 



Dafila acuta ... .16 



Bernicla canadensis . . 18 



Mergus merganser . . . .18 



,, albicillus . . 16 



FIG. 216. MOUTH OF 

 Bizinra lobata (AFTEK 

 FORBES). 



p, pouch : /, tongne ;f.l, fra?iium 

 lingua?. 



The tongue is strong and 

 bordered with spines. In Mergus 

 only is it thin and pointed. 



The liver has a large gall 

 bladder. 



Biziura lobata is unique among 

 Anseres 2 in having a subgular pouch (fig. 216), formed by a 

 duplicature of the fraenum linguae. 



The most noteworthy point that appears from the facts 

 given on the next page is the gradual reduction of the caeca 

 in the mergansers and smews, and the great range of variation 

 in size which they exhibit in Cygnus iiit/r/coUi.s, a variation 



XIT/SCH says 16. 



- Cf. Glides for si similar structure. 



