292 On the Anaton.y of the Hoatzin. 



Garrod*. The incorrect figure of this organ given by Young 

 has been ah'eady referred to (p. 285). 



The principal features in the structure of the syrinx are 

 illustrated in Garrod's figure ; but I find that the box formed 

 by the union of tlie last tracheal and upper bronchial rings 

 may be composed of more elements than are represented in 

 his fig. 1. There is^ iu fact, some variation in the adults 

 examined by me in the number of rings -which unite to 

 form this box (p. 291) ; this part of the windpipe is 

 not unlike the corresponding region of Indicator ■\. The 

 syringeal muscles (intrinsic) end, as Garrod shows, upon one 

 of the free tracheal rings immediately preceding the fused 

 rings. In Garrod's figure the muscle is continued into a 

 tissue which is differently shaded, and presumably represents a 

 fibrous baud ; this is inserted into the following ring. In some 

 specimens examined by me the fibrous continuation of the 

 muscles extends along the windpipe as far as the first or second 

 bronchial ring ; the fibrous band is composed of a very tough 

 tissue. It appears to me to be legitimate to compare this 

 with a band of fibroid tissue which occupies the place of 

 the absent syringeal muscles in BalcenicepsX, and which I 

 have considered to be the degenerate equivalent of those 

 muscles. In Opisthoconius it will be noticed that the 

 fibrous continuations of the syringeal muscles are attached to 

 the bronchial semiring, to which it is most usual in birds to 

 find these muscles attached. It is probable that, as the last 

 tracheal and first bronchial rings become consolidated into 

 the box-like structure of the adult, the atrophy of the 

 muscle commences below the top of the box. The move- 

 ments of the first bronchial rings could be as easily eff'ected 

 by the attachment of the muscle to the top of the box, and 



* Coll. Papers, p. 466. 



t Garrod, "Notes on the Anatomy oi Indicator major,'''' P. Z. S. 1878, 

 p. 935, and Coll. Papers, p. 464, fig. 3. 



X " On Certain Points in the Structure of Baheniceps bearing upon its 

 Affinities,'' P. Z. S. 1888, p. 284. Prof. Parker ('' On the Systematic 

 Position of the Crested Screamer," P. Z. S. 186.3, p. 514) has observed 

 that in that bird the intrinsic muscles of the syrinx end in a fau-shaped 

 fascia. 



