254 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
c. THe WInNDPIPE. 
The most valuable of the numerous treatises on the windpipe of the Paleognathe 
—tfrom 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, however, 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 much 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. oweni. 
There is a feeble vocal cord, and the lateral muscles stop at the insertion of the 
sterno-tracheales. 
Casuarius, 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 membrana 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 
