234 ON THE TKACHEA IN THE " RATITE " BIRDS. 



more cylindrical than its predecessors ; it is also wider transversely, 

 and incomplete behind in the middle line, its extremities, however, being 

 closely approximated to each other. The last tracheal ring is still wider 

 transversely, and more cylindrical ; and it too is incomplete posteriorly, 

 to a greater extent than its predecessor ; viewed from the side it is 

 convex upwards, as are its few immediate predecessors in a less degree. 

 The interannular intervals between all these rings are, when undisturbed, 

 mere chinks filled up by dense fibrous and elastic tissues. There is no 

 trace of a pessulus, though the last tracheal ring is slightly produced 

 downwards in front. The first bronchial semiring, on each side, is 

 narrow and cylindrical, strongest anteriorly, and somewhat attenuated 

 posteriorly. It is separated only by a narrow interval from the last 

 tracheal ring. The second and third rings are similar, but are more 

 slender and lengthy ; they are convex downwards, but very slightly so ; 

 hence the interannular intervals are small here also. Their anterior 

 ends are very slightly inturned, impinging but to a small extent on the 

 membrana tympaniformis, which completes the bronchial tubes internally, 

 and, in consequence of the absence of any three-way piece, passes con- 

 tinuously from one bronchus to the other, so closing the tracheal tube 

 inferiorly. The fourth, fifth, and succeeding bronchial rings are similar 

 in character ; but their ends, which tend to be dilated posteriorly, are 

 successively more and more incurved to about the tenth. Nowhere are 

 the bronchial rings complete. 



There is, at most, only a trace of a membrana semilunaris, in the form 

 of a very feeble, scarcely raised, antero-posteriorly directed fold of 

 mucous membrane. 



Internally, 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 (vide fig. 1, 6). 



There is no trace of any intrinsic voice-muscle ; and the lateral tra- 

 cheal muscles stop at the point of insertion of the sterno-tracheales. 



The genus Apteryx, in the simplicity of the structure of its lower larynx, 

 stands on the same level as Struthio. In Apteryx mantelli (figs. 3, 4) 

 about the last dozen tracheal rings are quite simple in form, with narrow 

 interannular intervals, and no anterior and posterior notching. The 

 penultimate ring is produced slightly downwards, in a triangular way, 

 both anteriorly and posteriorly. The last ring is also produced down- 

 RZ. S. 1881, wards anteriorly, but is incomplete in the middle line behind; it is 

 p. 781. slightly wider and stronger than the preceding rings. The first two 

 bronchial semirings on each side closely resemble it in form ; the first 

 semirings of opposite sides are almost in contact at both extremities, the 

 next pair being more widely separated at those joints. There is only a 

 narrow space between the last tracheal and the first bronchial ring. The 



