254 ME. W. p. PTCKAFT ON THE MORPHOLOGY AjN'I) 



c. The AVindpipe. 



The most valuable of the numerous treatises on the windpipe of the Palceognathw 

 — from a systematic point of view — is that by Forbes [20]. We are concerned here 

 only with the thoracic end of the trachea, and the degree of specialization which it has 

 reached in the direction of the formation of a " syrinx." 



Struthio and Apteryx, up to the time of Mr. Beddard's paper [8], have been held 

 to represent the least specialized forms in this particular. 



In Struthio there are no intrinsic muscles. There is a membrana tympaniformis 

 interna, but only a trace of a membrana semilunaris. " Internally," according to 

 Forbes, " the mucous membrane of the interior is greatly thickened, forming a vocal 

 cord, in the region of the last three tracheal rings and first two bronchial semirings. 

 The lateral tracheal muscles stop at the point of insertion of the sterno-tracheales!' 



In Apteryx there is a broad membrana tympaniformis interna and a feeble 

 membrana semilunaris. As in Struthio there is no pessulus and, it was believed, no 

 intrinsic muscles. 



Mr. Beddard's dissections, howe\er, showed that these were " especially plainly 

 developed in Apteryx australis." In this species he found " a thin band of muscle 

 continuous above with the extrinsic muscle ; this passes down the side of the trachea 

 and gradually thins out into fibrous tissue, which seems to die away upon the last 

 tracheal ring, hardly reaching the bronchi. Its state, in fact, is clearly one of degenera- 

 tion, and very mucli on a par with the state of the corresponding muscle in the 

 Hoatzin (Opisthocomus). In A. mantelli the same muscle was visible, but it did not 

 seem to be anything like so well developed as it is in the species first referred to." 



It appears to be entirely wanting in A. haastii and A. oiveni. 



There is a feeble vocal cord, and the lateral muscles stop at the insertion of the 

 sterno-tracheales. 



Casuaritis, as Forbes remarks, shows one interesting peculiarity, the lower end of 

 the trachea becoming slightly dilated above the bronchi. Furthermore, the last 

 tracheal rings are incomplete behind, the median space to which this gives rise being 

 filled up by fibrous and elastic tissue arranged transversely. By the contraction of 

 this, after death, the ends of the rings are drawn inwards, so forming within the 

 tube a low longitudinal ridge, resembling the tracheal septum of certain Petrels 

 and Penguins. 



There is no pessulus, the membrana tympaniformis interna passing over from one 

 bronchus into the other. A very slight thickening of this membrane in the middle 

 line between the two bronchi suggests a memh-ana semilunaris, but, as Forbes 

 remarks, there is nothing that can properly be called by this name. The outer vocal 

 cord is well developed. 



Forbes describes, but so far I am not able to confirm this, " On the internal wall of 



