364 STRUCTURE AND CLASSIFICATION OF BIRDS 



The cmca vary considerably in their development, as the 

 following table of measurements shows : — 



The lobes of the liver are subequal in Sterna, Anous, 

 Gygis, and Bissa. In Larus and Lestris the right is the 

 larger. A gall bladder is always present. 



fa Anous the cceca are quite short ; in Gygis long and 

 char adr line. 



The syrinx of this family is typically tracheo-bronchial 

 (at any rate in Larus), with well-developed muscles, which 

 always reach the bronchi. The family thus differs from 

 other Limicolae where there is a tendency towards a retro- 

 gression of the intrinsic muscles, sometimes culminating in 

 actual disappearance. 



In Larus marinus the last six or seven tracheal rings 

 are rather narrower from above downwards than those 

 which precede them, and are more or less firmly attached 

 (except the last ring, which is incomplete both in front and 

 behind) to form a box. When the syrinx is viewed from 

 behind, a broad three-way piece is seen, into the formation of 

 which the penultimate tracheal ring and the four or five in 

 front of it appear to enter. This piece, however, is only 

 really solid at the edges, the bars being a continuation of 

 the penultimate tracheal rings. In the middle it is so thin 

 as to be little more than a membrane. The first bronchial 

 semi-ring (to which the intrinsic muscles are attached) is 

 bow-shaped and in close contact with the last tracheal ring. 

 The remaining semi-rings are narrower and run in a straight 

 direction across the bronchi. 



The membrana tympaniformis is distinguished by its 



